Carbonylation of Polyfluorinated Alkylbenzenes and Benzocycloalkenes at the Benzyl C-F and C-Cl Bonds Under the Action of CO/SbF₅

Abstract

The carbonylation at the benzyl C-Hal bonds (Hal = F, Cl) of a number of polyfluorinated alkylbenzenes and benzocycloalkenes using carbon monoxide in the presence of SbF₅ is described. The reaction provided the corresponding α-arylcarboxylic acids or their methyl esters following aqueous or methanol treatment. The products of double carbonylation were obtained from bis(chloromethyl)tetrafluorobenzenes and benzal fluorides. For benzal chloride derivatives, the possibility of selective mono- or dicarbonylation was shown to depend on the amount of antimony pentafluoride. In the case of polyfluorinated secondary benzyl halides with a hydrogen atom at the α-carbon atom and vicinal fluorine atoms, the addition of CO was found to be accompanied by the elimination of HF, resulting in α,β-unsaturated α-arylcarboxylic acids. The double elimination of HF during the carbonylation of 1,4-dichloro-2,2,3,3,5,6,7,8-octafluorotetralin yielded dimethyl perfluoronaphthalene-1,4-dicarboxylate.

1. Introduction

Organofluorine compounds are objects of interest for basic research in organic chemistry as well as for application-oriented research in materials science, biomedicine, and agriculture [1,2,3,4,5,6,7,8,9,10]. Therefore, the development of new synthetic methods to novel fluorinated building blocks is of great importance for the future of the science. In the chemistry of non-fluorinated hydrocarbons and their derivatives, there are many well-known examples of carbonylation reactions catalyzed by acids (Brønsted or Lewis) that are applicable to alkyl halides, alcohols, and other compounds able to generate carbocations in acidic systems, and these reactions, proceeding via the CO addition to a carbocation, yield carboxylic acid derivatives [11,12,13]. In contrast to a plethora of reactions involving fluorinated cations, the acid-catalyzed carbonylation of polyfluorinated species had not been known before our recent studies [14,15,16,17,18], while a reverse reaction—decarbonylation of fluorinated acyl halides under the action of Lewis acids—is common [19,20,21,22]. The examination of the acid-catalyzed carbonylation of organofluorine compounds—accounting only for those substrates where fluorine atoms influence the reaction center—has showed that the examples are limited to mono- and difluoro-substituted diarylcarbinols [23], and to mono-(polyfluoroalkyl)-substituted adamantyl halides [24,25] (Scheme 1a).

Both transition metal-catalyzed carbonylation at a C(sp³)–X bond (X = Hal, OR) and the hydrocarboxylation or hydroesterification of alkenes provide an alternative to acid-catalyzed carbonylation, with both of these methods resulting in carboxylic acids or their derivatives. These approaches have more examples for fluorinated compounds (Scheme 1b–d), but the scope of substrates is quite small, and there is only little evidence regarding polyfluorinated species. For instance, aliphatic carboxylic acids with a perfluoroalkyl moiety (that can be quite long) at the β-position were synthesized by a Pd-, Ru-, or Co-catalyzed carbonylation of polyfluorinated alkyl iodides (Scheme 1b) [26,27,28,29,30,31,32]; Pd-catalyzed hydrocarboxylation and hydroesterification of perfluoroalkyl-substituted ethylenes using CO [33,34,35,36,37] were also employed to obtain the acids and their derivatives (Scheme 1b). For the synthesis of α-CF₂H-substituted arylacetic acid esters, a Pd-catalyzed hydroesterification of 1,1-difluoro-2-arylethylenes was used [38] (Scheme 1c). Another case in point is a Pd- or Co-catalyzed carbonylation of primary benzyl derivatives ArCH₂X [39,40,41,42,43,44,45,46,47,48] and esters of allylic alcohols [49,50], but fluorinated examples featured only substrates with one fluorine atom or CF₃ group at the aryl moiety or at the double bond (Scheme 1d).

Previously, we demonstrated the use of a carbonylation reaction for the introduction of functional groups to some polyfluorinated and even perfluorinated compounds (Scheme 2). We found that perfluorinated benzocyclobutenes [14,15] and their carbonyl derivatives [17] undergo carbonylation/four-membered ring-opening tandem reactions in the presence of carbon monoxide and SbF₅ (Scheme 2a). In these reactions, an irreversible four-membered ring transformation promotes the conversion of polyfluorobenzocyclobutenes into the final products. The carbonylation of per- and polyfluorinated indanes and tetralins, leading to fluorocarbonyl derivatives or corresponding acids (if subjected to hydrolysis), was also demonstrated by performing the reaction in the CO–SbF₅ system [16]. In this case, when the substrate has a five- or six-membered cycloalkyl ring, no skeletal rearrangements occurred and the carbonylation proceeds as an equilibrium process, with the conversion substantially depending on the substrate structure (Scheme 2b). Recently, we have developed a carbonylation procedure for a series of polyfluorinated alkylbenzenes and benzocycloalkenes with primary, secondary, or tertiary OH groups at benzylic positions using CO in the presence of superacids, the method allowed obtaining the corresponding mono- and dicarboxylic acids or lactones [18] (Scheme 2c).

In continuation of our study on the carbonylation of polyfluorinated compounds, we now have focused on various benzyl halides. The current work describes the carbonylation of a series of polyfluorinated benzyl halides Ar_FCHHalR (R = Hal, H, C₆F₅, Alk_F) in the CO–SbF₅ system. The developed method allows transformation of the above compounds into -COOH or -COOR derivatives (Scheme 2d). Synthesized by this method, polyfluorinated α-aryl-substituted carboxylic acids are now being considered to be used as building blocks for bioactive compounds, because similar acids and esters with fluorine atoms in both aliphatic and aromatic moieties have been investigated for use in medicine [51,52,53,54,55,56], as it is in the case of halogenated derivatives of benzocycloalkene-1-carboxylic acids [57,58,59,60,61]. Polyfluorinated aromatic moieties in a molecule would allow further synthetic modifications via S_NAr substitution. Additionally, the perfluorinated aryl group has unique physicochemical properties that can be used in the design of materials. For instance, derivatives of pentafluorophenyl acetic acid have been utilized to create gas sensors [62], supramolecular associates for biological applications [63,64], and semiconductor and photoluminescent materials [65,66].

2. Results and Discussion

2.1. Carbonylation of Polyfluorinated Aromatic Compounds with CF₂H and CCl₂H Groups

We showed that the CF₂H and CCl₂H groups in polyfluorinated benzal fluorides 1a–c and benzal chlorides 2a,d underwent transformation upon reaction with CO in a SbF₅ medium at room temperature under atmospheric pressure, which resulted in dicarbonylation products (

Table 1. Carbonylation of compounds 1a–c and 2a,d in the CO–SbF₅ system.

Entry	Substrate	ArF	Hal	SbF5 (Equiv)	Time (h)	Product/Content {Yield} a (%)
1	1a	C6F5	F	1	2.5	3a/64 b
2	″	″	F	2	2.5	3′a/92
3	″	″	F	5.3	6	3′a/96 {90}
4	1b	Perfluoroindan-5-yl	F	5.9	3.25	3′b/85 {76}
5	1c	Perfluorotetralin-6-yl	F	1	0.75	3′c/30
6	″	″	F	6	3.25	3′c/90 {81}
7	2a	C6F5	Cl	0.5	3	6a/41
8	″	″	Cl	1	2.5	6a/89 {69}
9	″	″	Cl	1	3	6′a/86 {47}
10	″	″	Cl	2	3	6′a/76
11	″	″	Cl	4	3	3′a/35
12	″	″	Cl	6	4.5	3′a/25
13	2d	p-CF3C6F4	Cl	1	1.75	6d/70 {65}
14	″	″	Cl	5.8	3.25	3′d/80 {64}

^a Isolated yield. ^b The mixture also contained 6% of its decarboxylation product 9a.

). Thus, assisted by SbF₅, compound 1a added two CO molecules to produce malonate 3′a following methanol treatment (an aqueous treatment yielded the corresponding diacid 3a, which was unstable, being prone to decarboxylation [67], and slowly decomposed in an Et₂O solution to phenylacetic acid). Using compound 1a, we showed that the highest conversion (96%) to the carbonylation product was achieved with an excess of SbF₅ (Table 1, entries 1–3). The addition of CO to the alicyclic moiety of indan 1b, as in the case of a number of other polyfluoroindanes [16], did not occur to a considerable extent.

The behavior of benzal chloride 2a and benzal fluoride 1a differed, and the conversion of compound 2a to product 3′a in the reaction with an excess of SbF₅ reached only 35% (Table 1, entries 11, 12). The low conversion was probably due to the greater stability of the corresponding chlorine-substituted benzyl cation 4, as compared with a fluorine-substituted counterpart. The CF₃ group in compound 2d decreases the stability of the benzyl cations 4 and 5 generated from it; as a result, its conversion into the dicarbonylation product under similar conditions was much higher (Table 1, entry 14).

We should note that the CF₃ group in compound 2d and CF₃ groups in the other trifluoromethyl-substituted benzenes used in this work were unreactive towards CO addition; this observation agrees that the reverse reaction—the decarbonylation of Ar_F CF₂COF under the action of SbF₅—is much more highly favored [22].

Reducing the amount of SbF₅ resulted in the selective monocarbonylation of compounds 2a,d, yielding chloroacetic acids 6a,d, or ester 6′a (Table 1, entries 8, 9, 13). The highest content of the monocarbonylation products was achieved using 1 equiv. of SbF₅ (Table 1, entries 7–10). But in contrast to this, the use of 1 equiv. of SbF₅ in the case of difluoromethyl derivatives 1a,c (Table 1, entries 1, 5) afforded a mixture of dicarbonylation products, along with the starting compounds and the solvolysis products of the cations from the starting compound (Ar_FCH(OMe)₂ and Ar_FCHO). Monocarbonylation products were not formed in considerable amounts.

2.2. Carbonylation of Polyfluorinated Aromatic Compounds with CH₂F and CH₂Cl Groups

A number of polyfluorinated primary benzyl fluorides 7 and benzyl chlorides 8 selectively reacted with CO in the SbF₅ medium to give the corresponding arylacetic acids 9 following hydrolysis of the reaction mixtures (

Table 2. Carbonylation of benzyl halides 7a,d and 8a,d–h in the CO–SbF₅ system and alcohols 14 d–f in superacids.

Entry	Substrate	R	X	SbF5 (Equiv)	TfOH (Equiv)	Time (h)	t (°C)	Product/Content {Yield} a (%)
1	7a	F	F	0.5	-	2	r.t.	9a/15
2	″	″	F	2	-	0.75	r.t.	9a/10
3	″	″	F	3.8	-	0.75	r.t.	9a/75
4	″	″	F	6	-	0.75	r.t.	9a/90 {86}
5	8a	F	Cl	0.5	-	2	r.t.	9a/10
6	″	″	Cl	6	-	0.75	r.t.	9a/90 {87}
7	7d	p-CF3	F	6.1	-	1	r.t.	9d/6
8	8d	p-CF3	Cl	5.9	-	2.5	r.t.	9d/6
9	8e	m-CF3	Cl	6	-	0.75	r.t.	9e/90 {85}
10	8f	o-C6F4	Cl	5.9	-	0.75	r.t.	9f/92 {88}
11	8g	p-CF(CF3)2	Cl	6.1	-	1.5	r.t.	9g/20 {11}
12	8h	p-C6F5	Cl	6	-	2	r.t.	9h/5 {3}
13	14d	p-CF3	OH	3	3	7	60	9d/88 {65}
14	14e	m-CF3	OH	-	7	6	50	9e/85 {64}
15	14f	o-CF3	OH	-	7	6	75	9f/95 {75}

^a Isolated yield.

). Previously, for the carbonylation of pentafluorobenzyl alcohol (C₆F₅CH₂OH) we used the CO–TfOH system at 50 °C, and phenylacetic acid 9a was the only product obtained with a 90% yield [18]. The carbonation of benzyl fluoride 7a, as well as benzyl chloride 8a, in the CO–SbF₅ system at room temperature resulted in a similar yield of acid 9a (Table 2, entries 4, 6). The reactions proceeded smoothly with an excess of SbF₅, ensuring the complete conversion of the starting compound into a benzyl cation; a decrease in the SbF₅ amount (Table 2, entries 1–3, 5) facilitated side reactions leading to resinous byproduct formation.

Ortho- and meta-CF₃ derivatives 8e,f were also shown to be able to be selectively carbonylated into arylacetic acids 9e,f (Table 2, entries 9, 10). Despite the use of an excess of SbF₅, the formation of corresponding 2- and 3-(carboxymethyl)tetrafluorobenzoic acids 10 and 11—as a result of the conversion of the CF₃ group upon hydrolysis—occurred only to a small extent and the yield of such products did not exceed 10%. In contrast to isomers 8e,f, the carbonylation of the para-CF₃ derivative 8d in the CO–SbF₅ system was unsuccessful, as was the case with benzyl fluoride 7d (Table 2, entries 7, 8). The reaction resulted in a complex mixture of compounds, in which acid 9d was detected only in small amounts as well as 4-(carboxymethyl)tetrafluorobenzoic acid 12. This result was apparently owing to side transformations of compounds 7d and 8d in SbF₅, which occurred instead of carbonylation, since the formation of a complex mixture of products was also observed in the absence of CO. One of the identified products formed in significant quantities in the reactions of compounds 7d and 8d was 4-methyltetrafluorobenzoic acid 13, which indicates the occurrence of oxidation-reduction processes in the SbF₅ medium. The replacement of the CF₃ group in compound 8d with a perfluoroisopropyl group or with a pentafluorophenyl group did not significantly change the result of the reactions of the corresponding benzyl chlorides, 8g,h, with CO–SbF₅. The reactions resulted in multicomponent mixtures with a low content of acids 9g,h (Table 2, entries 11, 12).

The unsatisfactory result of the carbonylation of para-CF₃ derivatives 7d and 8d aroused an interest to study the possibility of carbonylation of the corresponding alcohol 14d in superacids using our previously proposed method [18]. We demonstrated that its interaction with CO in an equimolar mixture of TfOH–SbF₅ at 60 °C led quite selectively to acid 9d (Table 2, entry 13). Complete conversion to the carbonylation product required rather vigorous conditions, and, as a result, 4-(carboxymethyl)tetrafluorobenzoic acid 12 was also formed as a byproduct. The formation of other byproducts in significant amounts was not observed in this reaction. The isomeric alcohols 14e,f can be selectively carbonylated in a less acidic medium, such as TfOH, without addition of SbF₅, at 50 or 75 °C, respectively (Table 2, entries 14, 15).

We previously reported the carbonylation of bis(hydroxymethyl)tetra fluoro benzenes in superacids, the para- and meta-isomers selectively transformed into the corresponding dicarboxylic acids, whereas the ortho-isomer added only one molecule of CO, thereby yielding 5,6,7,8-tetrafluoroisochroman-3-one (15) [18]. The result of the carbonylation of bis(chloromethyl)tetrafluorobenzenes 16a–c in the CO–SbF₅ system was different (

Table 3. Carbonylation of compounds 16a–c in the CO–SbF₅ system.

Entry	Substrate	Substitution Pattern	SbF5 (Equiv)	Time (h)	Product/Content {Yield} a (%)
1	16a	para	6.4	2	17′a/15
2	16b	meta	6.5	2	17′b/65 {44}
3	16c	ortho	6	1	17′c/86
4	″	″	6.9	2.5	17c/80 {67}

^a Isolated yield.

). The carbonylation of the para-isomer 16a, as in the case of para-substituted benzyl halides 8d,g,h, resulted in a mixture of products; dicarboxylic acid ester 17′a was detected in the reaction mixture obtained after the methanol treatment, but its content did not exceed 15%, while the products of redox transformations containing the Ar_F-CH₃ moiety were also observed. The carbonylation of the meta-isomer 16b proceeded more selectively, but resinification did occur, which reduced the yield of ester 17′b. Ortho-isomer 16c reacted with two CO molecules without resinification, the main product was diacid 17c or its methyl ester 17′c depending on subsequent treatment, and the admixture of lactone 15, a monocarbonylation product, in the reaction mixture did not exceed 10%.

2.3. Carbonylation of Polyfluorinated Diphenylmethanes (C₆F₅)₂CHHal

It was shown that benzyl halides 18 and 19 can be converted to acid 20 by carbonylation in the CO–SbF₅ system with subsequent aqueous treatment of the reaction mixture (

Table 4. Carbonylation of compounds 18 and 19 in the CO–SbF₅ system.

Entry	Substrate	Hal	SbF5 (Equiv)	Time (h)	Content {Yield} a of Acid 20 (%)
1	18	F	0.5	6	45
2	″	F	1	4.5	50 {44}
3	″	F	2.1	4.5	4
4	″	F	6	5.5	3
5	19	Cl	0.5	4.5	88 {85}
6	″	Cl	1	4.5	45
7	″	Cl	6	4.5	<1

^a Isolated yield.

).

The equilibrium of the carbonylation reaction of halogenated diphenylmethanes 18 and 19 in an excess of SbF₅ was strongly shifted toward bis(pentafluorophenyl)methyl cation 21 due to the high stability of the latter. With the use of 6 equiv. of SbF₅, the conversion to acid 20 did not exceed 3% (Table 4, entries 4, 7). Reducing the amount of SbF₅ to 0.5–1 equiv. for fluoro derivative 18 increased its conversion to acid 20 to 45–50% (Table 4, entries 1, 2), but with a lack of SbF₅ the formation of a solid salt of cation 21 occurred, which impeded the carbonylation of compound 18. The generation of cation 21 by the SbF₅-assisted cleavage of the chloride anion from 19 did not result in the formation of a solid salt precipitate (because of different counterion), and probably that is why the conversion of compound 19 to acid 20 in the presence of 0.5 equiv. of SbF₅ was significantly higher and reached 88% (Table 4, entry 5). The reaction mixture obtained after hydrolysis contained products (C₆F₅)₂CF₂ and (C₆F₅)₂CO. This finding apparently implies that a chlorine-mediated oxidation process (i.e., the substitution of a hydrogen atom by fluorine) took place, and it was followed by the formation of perfluorodiphenylmethyl cation.

2.4. Carbonylation of Polyfluorinated Aromatic Compounds with CHHalAlk_F Groups and the Concomitant Elimination of HF

The interaction of benzyl halides 22b,d and 23a–d with CO in a SbF₅ medium (

Table 5. Carbonylation of compounds 22b,d and 23a–d in the CO–SbF₅ system.

Entry	Substrate	R	Hal	SbF5 (eq.)	Time (h)	t (°C)	Product/Content {Yield} a (%)
							24/24′	25/25′	26
1	23a	F	Cl	0.5	1	r.t.	24a/71	-	-
2	″	″	Cl	1	1	r.t.	24a/>95 {92}	-	-
3	″	″	Cl	1	1.5	r.t.	24′a/>95 {90}	-	-
4	″	″	Cl	6	0.5	r.t.	24a/>95 {96}	-	-
5	22b	CF3	F	1	0.5	r.t.	24b/86	25b/9	26b/5
6	″	″	F	2	0.5	r.t.	24b/90	25b/9	26b/1
7	″	″	F	4	0.5	r.t.	24b/95	25b/5	-
8	″	″	F	6	0.5	r.t.	24b/95 {81}	25b/5	-
9	″	″	F	6	6	70	-	25′b/72 b {69}	-
10	23b	CF3	Cl	1	1	r.t.	24b/89	25b/5	26b/6
11	″	″	Cl	6	1	r.t.	24b/95	25b/5	-
12	″	″	Cl	6	5	r.t.	24b/91	25b/9	-
13	″	″	Cl	6	1	70	24b/36	25b/60	26b/4
14	″	″	Cl	6	5	70	24b/2	25b/92	26b/6
15	23c	–CF2CF2–	Cl	1	1	r.t.	24c/81	25c/7	26c/12
16	″	″	Cl	6	1	r.t.	24c/87 {59}	25c/13
17	″	″	Cl	6	1	70	-	25c/94 {68}	26c/6
18	22d	–CF2–	F	1	0.5	r.t.	24d/95 {79}	-	-
19	23d	–CF2–	Cl	1	1	r.t.	24d/50	-	-
20	″	″	Cl	6	0.5	r.t.	24d/50	-	-

^a Isolated yield. ^b The mixture also contained 18% of acid 25b.

) occurred more readily as compared to diphenylmethanes 18 and 19 (Table 4). A perfluoroalkyl group at the reaction center reduces the stability of the intermediate benzyl carbocation, thus increasing its reactivity; as a result, the carbonylation of chloro-derivatives 23a–c and fluoro-derivatives 22b,d occurred with complete conversion both in an excess of SbF₅ and with one equiv. of SbF₅. Using 23a as a model compound, we demonstrated that further reduction in the SbF₅ amount to 0.5 equiv. resulted in incomplete conversion of the starting compound (Table 5, entry 1).

Since benzyl halides 22 and 23 have a perfluoroalkyl group at the α-carbon atom, their carbonylation can be accompanied by elimination of HF, thus giving rise to α,β-unsaturated carboxylic acids and esters 25 and 25′ along with, or instead of, saturated products 24 and 24′ (Table 5). The reaction of compound 23a at room temperature selectively gave products 24a or 24′a, without appreciable contribution from the HF elimination process. Whereas after the carbonylation of compounds 22b and 23b,c in an excess of SbF₅ (4–6 equiv.) at room temperature, along with acids 24b,c, small amounts of α,β-unsaturated acids 25b,c were obtained (Table 5, entries 7, 8, 11, 16); and if 1–2 equiv. of SbF₅ was used, the formation of ketones 26b,c was also observed (Table 5, entries 5, 6, 10, 15). In these reactions prior to a workup, the carbonylation with the concomitant elimination of HF would result in cations 27b,c. During an aqueous workup, the formation of acids 25b,c from cations 27b,c is obvious. Ketones 26b,c were probably formed from the same cations 27b,c by the nucleophilic attack of a water molecule at the positively charged CF-position followed by the decarboxylation of the resulting ketoacid (Scheme 3). Therefore, compound 26 should be accounted for as an elimination product. In this regard, we can conclude that reducing the amount of SbF₅ does not reduce the contribution of the HF elimination process that accompanies carbonylation.

A fivefold increase in the reaction time for compound 23b increased the content of the elimination product 25b by less than twofold (Table 5, entries 11, 12), whereas an increase in temperature to 70 °C significantly shifted the product ratio in favor of elimination products decreasing the content of 24b,c up to their complete conversion (Table 5, entries 9, 13, 14, 17). The concomitant elimination of HF with the formation of α,β-unsaturated acids (including compounds 25b,c) was observed earlier [18] in the carbonylation of polyfluorinated secondary 1-arylalkan-1-ols in super acids, but complete conversion could not be achieved by the method [18].

The aforementioned HF elimination reactions occurred more easily for compound 23c with a six-membered aliphatic cycle compared to its acyclic analog 23b (chloro- and fluoro-derivatives 23b and 22b showed similar reactivity, Table 5). For compound 23a with a shorter aliphatic moiety, this process was even more unlikely and was observed only at elevated temperatures. In the case of compound 23a, it was not possible to isolate unsaturated acid 25a or its ester 25′a from the reaction mixture obtained by its carbonylation in a CO–SbF₅ system at 70 °C (Scheme 4) due to the significantly greater reactivity of these compounds containing two geminal fluorine atoms at the double bond toward nucleophilic addition reactions. Hydrolysis of the reaction mixture followed by extraction with Et₂O yielded a mixture of three major products 3a, 24a, and 25a, with the former predominating (Scheme 4). Compound 3a apparently resulted from the addition of water to the double bond of acid 25a during aqueous treatment. However, even after drying the Et₂O extract over MgSO₄, the content of acid 25a in the solution rapidly decreased, probably due to its reaction with traces of water. When the reaction mixture was treated with methanol, the unsaturated ester 25′a was not detected at all. Instead, its adduct with methanol 28′ was present, which was the main reaction product, with the minor being compounds 3′a and 24′a.

In contrast to tetralin 23c, the carbonylation at room temperature of indan 22d with a five-membered alicyclic ring yielded only traces of the HF elimination product 25d. In the presence of 1 equiv. SbF₅, the compound 22d was smoothly converted into corresponding acid 24d (Table 5, entry 18). Moreover, the carbonylation reactions of indan 22d and tetralin 23c at 70 °C gave completely different results. The carbonylation of indan 22d in an excess of SbF₅ at 70 °C, followed by treatment with methanol, gave dicarboxylic ester 29′ instead of ester 25′d (Scheme 5). In addition, the reaction mixture also contained perfluorinated indan 30 and indanone 31. To explain the formation of products 29′ and 30 in these conditions, the following sequence of transformations can be proposed. The carbonylation of compound 22d yields carbonyl fluoride 32. Subsequent elimination of HF gives the corresponding indene, which then adds a second CO molecule affording compound 33. The indenyl cation generated from compound 33 is probably able to abstract a hydride ion from the initially formed carbonyl fluoride 32, thereby giving indene 34 that yielded product 29′ after a methanol workup. The oxidation product 35 of carbonyl fluoride 32 was then converted to perfluoroindan 30 via the addition of fluoride ion and decarbonylation.

Carbonylation of chloroindan 23d occurred with significantly lower selectivity (Table 5, entries 19, 20) if compared with the reaction of indan 22d or chlorotetralin 23c (Table 5, entries 15, 16, 18). Even though acid 24d was the main reaction product, it was formed alongside many byproducts, containing benzylic CFCl or CO moieties. We presume that, in this case, side reactions of the starting compound and/or of the carbonylation product took place, involving the substitution of a fluorine atom at the benzylic CF₂ moiety by chlorine. The resultant products are able to generate indanyl cations with a chlorine atom at the cationic center, and these cations would be more stable than those with a fluorine atom [68]. That is why after the water treatment of the reaction mixture, significant amounts of indanones (the hydrolysis products of chloroindanyl cations) and indanes with benzylic CFCl moiety were produced.

In the case of tetralin 36 containing two benzylic CHCl moieties, mono- or diarbonylation is possible, the degree of carbonylation was shown to depend on the amount of antimony pentafluoride. The main product of the reaction with 1 equiv. SbF₅ followed by a methanol treatment was monomethoxycarbonyl derivative 37′ (Scheme 6). The reaction mixture also contained naphthalenecarboxylic ester 38′, which was the product of HF elimination. Complete conversion of compound 37′ to naphthalene derivative 38′ was achieved by exposing the reaction mixture to NEt₃. In the presence of 6 equiv. SbF₅, compound 36 added two molecules of CO, and, at room temperature, the concomitant elimination of two HF molecules occurred completely, thereby yielding naphthalenedicarboxylic ester 39′ after treatment of the reaction mixture with methanol. The methanol workup required long time to convert the obtained carbonyl fluorides into esters 38′ and 39′, arguably because the fluorocarbonyl group at the α-carbon atom of polyfluoronaphthalenes is sterically hindered.

2.5. Starting Compounds

Chlorides 8a,d–h, 19, and 23a were obtained by the reaction of alcohols 14a,d–h, 40, and 41a with SOCl₂ at 75 °C or with PCl₅ at 100 °C (

Table 6. Synthesis of starting compounds 7a,d, 8a,d–h, 18, 19, and 23a.

Entry	R	R′	Alcohol, Yield a (%)	Chloride, Yield a (%)	Fluoride, Yield a (%)
1	C6F5	H	-	8a, 91 b	7a, 86
2	p-C6F4CF3	H	14d, 74	8d, 86 b	7d, 81
3	m-C6F4CF3	H	14e, 85	8e, 94 b	-
4	o-C6F4CF3	H	14f, 73	8f, 93 b	-
5	p-C6F4CF(CF3)2	H	14g, 90	8g, 93 b	-
6	p-C6F4C6F5	H	14h, 90	8h, 97 c	-
7	C6F5	C6F5	-	19, 98 c	18, 65
8	C6F5	CF3	-	23a, 85 c	-

^a Isolated yield. ^b SOCl₂ as the reagent. ^c PCl₅ as the reagent.

). Benzyl alcohols 14d–h were derived from carboxylic acids 42d–h, which were first converted into acyl chlorides via a reaction with SOCl₂ and then the acyl chlorides were reduced with LiBH₄. Fluorine derivatives 7a,d, and 18 were synthesized by heating of the corresponding chlorides 8a,d, and 19 with CsF at 250–260 °C without a solvent.

In contrast to alcohols 14a,d–g, the reaction of diol 43 with SOCl₂ under similar conditions gave mainly cyclic sulfite 44, and the target dichloride 16c was obtained in good yield by heating diol 43 with PCl₅ (Scheme 7).

In contrast to alcohol 41a, the reaction of its homolog 41b with PCl₅ not only yielded the target chloride 23b but also resulted in considerable amounts of the para-chloroderivative 45 (Scheme 8). The greater steric hindrance of the reaction center probably accounts for the side product, which apparently formed via a PCl₅-assisted S_N1 substitution of the OH group accompanied by the attack of a chloride ion at the sterically more accessible position, yielding propylidenecyclohexadiene 46. The subsequent elimination of one of the halogenide ions from the CFCl moiety and addition of a chloride ion to the benzylic position restores the aromaticity of the arene and yields a mixture of mono- and dichloroderivatives 23b and 45. Fluorine derivative 22b was obtained from alcohol 41b by the reaction with C₆F₅CF₃ and SbF₅ (Scheme 8). In this case, perfluorotoluene simultaneously acted as a donor of a fluoride ion to replace the OH group and as an acceptor of the oxygen, degrading into perfluorobenzoic acid.

When replacing the OH group of tetralinol 41c in the reaction with PCl₅ at 100 °C, the addition of chloride ion to the aromatic ring also occurred, but to a lesser extent compared to alcohol 41b, while subsequent rearomatization almost did not occur. As a result, non-aromatic triene isomer 47 was formed as minor product along with target 23c (Scheme 9). The interaction of this obtained mixture of compounds 23c and 47 with CO–SbF₅ gave carbonylation products 24c and 25c along with admixture (6–8%) of their monochloro-derivatives 48 and 49 with a chlorine atom in the aromatic moiety. The content of the latter was close to the content of compound 47 in the starting compound. This indicates that under the action of antimony pentafluoride on compound 47, the fluoride ion is predominantly abstracted, rather than the chloride ion, with the formation of a chlorine-substituted cation 50, which then reacts with CO. Dichlorotetralin 36, obtained by the interaction of diol 51 with PCl₅, apparently also contained an admixture of non-aromatic isomer 52, since its carbonylation gave diester 39′ with 8% of the chloro-derivative 53′ as an impurity.

In contrast to compounds 41b,c, the reaction of indanol 41d with PCl₅ at 100 °C gave no products with a chlorine atom in the aromatic moiety; however, along with the target chloroindan 23d, a considerable amount of non-volatile by-products quite similar to the starting alcohol was obtained, which were apparently its esters with phosphoric acid, and that explains the rather modest yield of the target compound (Scheme 9).

The other starting compounds were prepared according to the procedures outlined in the literature: CF₂H derivatives 1a–c [69], CCl₂H derivatives 2a,d [70], dichlorides 16a [71] and 16b [72], indane 22d [73], alcohols 14a, 40 [74], 41a–d, 51 [75], and diol 43c [18].

2.6. Structural Analysis of Compounds

The structures of new compounds were established by means of high-resolution mass spectrometry (HRMS), elemental analysis, and spectral characteristics (copies of the ¹H and ¹⁹F NMR spectra are available in Supplementary Materials). Signals in NMR spectra of compounds were assigned on the basis of chemical shifts of the signals, their fine structure, and integral intensities. The obtained compounds 20, 24a–d, 24′a,d, 25′b, 26c, 39′ [18], 9a [76], 10 [67], 30 [69], 31 [77] were identified by the comparison of ¹⁹F NMR findings with the data in the literature.

To confirm the structure of some products obtained in the reactions, we also synthesized compounds 11–13 in separate experiments and recorded their NMR spectra. Notably, 3- and 4-(Carboxymethyl)tetrafluorobenzoic acids 11 and 12 were obtained by the reaction of compounds 9e and 9d with CF₃CO₂H and SbF₅. This approach for synthesis of carbonyl derivatives was developed earlier, in [78]. Methylbenzoic acid 13 was obtained by hydrolysis of a solution of 4-methylheptafluorotoluene in SbF₅, according to the method in [79].

3. Materials and Methods

3.1. General Information

Analytical measurements and spectral analyses were carried out at the Multi-Access Chemical Research Center SB RAS. IR spectra were acquired on a Bruker Vector 22 IR (Bruker Corporation, Billerica, MA, USA) spectrophotometer. ¹⁹F, ¹H NMR spectra were recorded on a Bruker AV 300 (Bruker Corporation, USA) instrument (282.4 MHz, and 300 MHz, respectively). Chemical shifts are given in δ ppm from CCl₃F (¹⁹F) and TMS (¹H). Hexafluorobenzene C₆F₆ (¹⁹F, δ_F −162.9 ppm), residual CHCl₃ (¹H, δ_H 7.24 ppm), and acetone-d₅ (¹H, δ_H 2.04 ppm) served as internal standards. Spin–spin coupling constant values are given in Hz. Gas chromatography coupled with mass spectrometry (GC-MS) was performed on a Hewlett Packard G1081A (Agilent Technologies, Santa Clara, CA, USA) instrument equipped with a gas chromatograph Hewlett Packard 5890 and a mass selective detector HP 5971 (EI 70 eV). Molecular masses of the compounds were determined by HRMS with a Thermo Electron Corporation DFS (Thermo Electron, Karlsruhe, Germany) instrument (EI 70 eV). Elemental analysis was performed on an Eurovector EA 3000 (Eurovector, S.p.A., Pavia, Italy) automatic CHNS analyzer. Melting points were determined on an Electrothermal IA 9100 (Electrothermal, Chelmsford, UK) apparatus (1 °C/min). Contents of products in reaction mixtures were determined using ¹⁹F NMR spectroscopic data. Column chromatography was carried out on silica gel 60 (Merck, Darmstadt, Germany), particle size 0.063–0.200 mm).

Antimony pentafluoride was distilled under atmospheric pressure (bp 142–143 °C). TfOH was purchased from commercial sources (99% purity). Carbon monoxide was prepared by the decomposition of formic acid in concentrated sulfuric acid, and was additionally dried by passing it through a layer of concentrated sulfuric acid. All reactions were carried out in glassware.

3.2. Typical Carbonylation Procedures

a. A mixture of a substrate and SbF₅ (a substrate was added dropwise to SbF₅ under stirring and cooling the flask in an ice bath) was intensively stirred in a round-bottom glass flask (5–10 mL) in a slow flow of CO under atmospheric pressure. After the time (mentioned below for each experiment), the mixture was poured into 5% hydrochloric acid (10 mL per 1 g of SbF₅) and extracted three times with 3–5 mL of Et₂O (if not specified otherwise). The extract was dried over MgSO₄ and analyzed by ¹⁹F NMR spectroscopy.

b. A mixture of a substrate and SbF₅ (a substrate was added dropwise to SbF₅ under stirring and cooling of the flask in an ice bath) was intensively stirred in a round-bottom glass flask (5–10 mL) in a slow flow of CO under atmospheric pressure. The mixture was poured into methanol (10 mL per 1 g of SbF₅) cooled to −10–0 °C. The resulting solution was allowed to warm up until it reached room temperature, and then it was poured into 5% hydrochloric acid (7 mL per 1 mL of methanol) and extracted three times with 10–15 mL of CH₂Cl₂. The extract was dried over MgSO₄ and analyzed by ¹⁹F NMR spectroscopy.

The reaction scale was 0.6–2.4 mmol of a substrate. Reagent amounts, reaction conditions, and procedures for separation of mixtures and product isolation are detailed in the experiments below. In some experiments, C₆F₆ or (C₄F₉)O were added to the reaction mixture to reduce the viscosity of the mixture and aid mixing during dissolution of a starting alkyl halide in SbF₅ and/or during the carbonylation process. It is not advisable to use hexafluorobenzene C₆F₆ for chlorine-containing substrates because it readily undergoes chlorofluorination in the SbF₅ medium in the presence of nascent chloride ions.

3.3. Carbonylation Experiments

3.3.1. Carbonylation of (Difluoromethyl)pentafluorobenzene (1a)

a. Compound 1a (0.324 g, 1.49 mmol) and SbF₅ (0.320 g, 1.48 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (2.5 h, r.t.), gave a mixture of compounds 1a, 3a, 9a, and C₆F₅CHO in an 12:64:6:18 molar ratio. The content of a compound with CHF moiety (¹⁹F NMR: δ −182.2 (dm, J_H,F = 45.5) in the reaction mixture did not exceed 1%.

b. Compound 1a (0.190 g, 0.87 mmol), SbF₅ (0.387 g, 1.79 mmol) (molar ratio 1:2), and C₆F₆ (0.2 mL) according to the typical procedure (Section 3.2b) (2.5 h, r.t., 20 min in methanol), gave a mixture of compound 3′a and C₆F₅CH(OMe)₂ in a 92:8 molar ratio.

c. Compound 1a (0.504 g, 2.31 mmol) and SbF₅ (2.646 g, 12.22 mmol) (molar ratio 1:5.3), according to the typical procedure (Section 3.2b) (6 h, r.t., 20 min in methanol), gave a mixture of compound 3′a and C₆F₅CH(OMe)₂ in a 96:4 molar ratio. Silica gel column chromatography (CHCl₃ as the eluent) gave 0.622 g of ester 3′a (yield 90%)

Dimethyl 2-(perfluorophenyl)malonate (3′a). Colorless liquid. IR (film) ν, cm⁻¹: 2960 (CH), 1751 (C=O), 1525, 1508 [FAR (fluorinated aromatic ring)]. ¹H NMR (CDCl₃): δ 4.94 (s, 1H, CH), 3.79 (s, 6H, CH₃). ¹⁹F NMR (CDCl₃): δ −141.1 (m, 2F, F-ortho), −154.1 (tt, 1F, J_para,meta = 21, J_para,ortho = 2, F-para), −162.5 (m, 2F, F-meta). HRMS, m/z: calcd. for C₁₁H₇O₄F₅ 298.0259; found 298.0260.

3.3.2. Carbonylation of 5-(Difluoromethyl)nonafluoroindan (1b)

Compound 1b (0.532 g, 1.61 mmol) and SbF₅ (2.076 g, 9.59 mmol) (molar ratio 1:5.9), according to the typical procedure (Section 3.2b) (3 h 15 min, r.t., 10 min in methanol), gave a mixture of compounds containing ~85% of ester 3′b. Silica gel column chromatography (with CH₂Cl₂ as the eluent) gave 0.503 g of ester 3′b (yield 76%).

Dimethyl 2-(perfluoroindan-5-yl)malonate (3′b). Colorless liquid. IR (film) ν, cm⁻¹: 2962 (CH), 1757 (C=O), 1504 (FAR). ¹H NMR (CDCl₃): δ 5.06 (s, 1H, CH), 3.82 (s, 6H, CH₃). ¹⁹F NMR (CDCl₃): δ −107.7 (m, 2F, CF₂-1 or 3), −108.4 (m, 2F, CF₂-1 or 3), −117.0 (dtd, 1F, F-4), −121.9 (dd, 1F, F-6), −130.7 (quintet, 2F, CF₂-2), −141.4 (ddt, 1F, F-7); J_1,2 = J_2,3 = 4, J_1,7 = 7, J_3,4 = 7.5, J_4,6 = 5, J_4,7 = 20, J_5,6 = 19, J_6,7 = 20.5. HRMS, m/z: calcd. for C₁₄H₇O₄F₉ 410.0195; found 410.0197.

3.3.3. Carbonylation of 6-(Difluoromethyl)undecafluorotertalin (1c)

a. Compound 1c (0.575 g, 1.51 mmol) and SbF₅ (1.978 g, 9.14 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2b) (2 h 15 min, r.t., 10 min in methanol), gave a mixture of compounds containing ~90% of ester 3′c. Silica gel column chromatography (CH₂Cl₂ as the eluent) gave 0.562 g of ester 3′c (yield 81%).

b. Compound 1c (0.467 g, 1.23 mmol) and SbF₅ (0.267 g, 1.23 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2b) (45 min, r.t., 10 min in methanol), gave a mixture of compounds containing 55% of starting compound 1c and 30% of ester 3′c. Content of a compound with CHF moiety (¹⁹F NMR: δ −186.9 (dm, J_H,F = 45.5)) did not exceed 5%.

Dimethyl 2-(perfluorotertalin-6-yl)malonate (3′c). Colorless liquid. IR (film) ν, cm⁻¹: 2962 (CH), 1753 (C=O), 1495, 1482 (FAR). ¹H NMR (CDCl₃): δ 5.07 (s, 1H, CH), 3.82 (s, 6H, CH₃). ¹⁹F NMR (CDCl₃): δ −106.5 (m, 2F, CF₂-1 or 4), −107.2 (m, 2F, CF₂-1 or 4), −113.6 (tdd, 1F, F-4), −122.7 (dd, 1F, F-6), −135.4 (m, 2F, CF₂-2 or 3), −135.6 (m, 2F, CF₂-2 or 3), −138.5 (qd, 1F, F-7); J_4,5 = 22, J_5,7 = 6, J_5,8 = 15, J_7,8 = J_1,8 = 20.5. HRMS, m/z: calcd. for C₁₅H₇O₄F₁₁ 460.0163; found 460.0167.

3.3.4. Carbonylation of (Dichloromethyl)pentafluorobenzene (2a)

a. Compound 2a (0.467 g, 1.86 mmol) and SbF₅ (0.202 g, 0.93 mmol) (molar ratio 1:0.5) according to the typical procedure (Section 3.2a) (3 h, r.t.), gave a mixture of compounds 1a, 2a, 6a, and C₆F₅CHO in a 5:44:41:10 molar ratio.

b. Compound 2a (0.524 g, 2.09 mmol), SbF₅ (0.458 g, 2.12 mmol) (molar ratio 1:1), and C₆F₆ (0.3 mL, was added 2.5 h after the start of carbonylation) according to the typical procedure (Section 3.2a) (3 h, r.t.), gave a mixture of compounds 1a, 2a, 6a, and C₆F₅CHO in an 1:3:89:7 molar ratio. Evaporation of the solvent and sublimation (110 °C, 3 Torr) afforded 0.373 g (yield 69%) of acid 6a.

c. Compound 2a (0.390 g, 1.55 mmol), SbF₅ (0.355 g, 1.55 mmol) (molar ratio 1:1), and C₆F₆ (0.3 mL, was added 2 h after the start of carbonylation) according to the typical procedure (Section 3.2b) (3 h, r.t., 15 min in methanol), gave a mixture of compounds 1a, 2a, 6′a, C₆F₅CHO, and C₆F₅CH(OMe)₂ in an 1:3:86:3:7 molar ratio. Silica gel column chromatography (CCl₄–CH₂Cl₂ [1:1, v/v] as the eluent) gave 0.199 g of ester 6′a (yield 47%), such modest yield is due to the difficulty of separating from other products.

d. Compound 2a (0.498 g, 1.98 mmol), SbF₅ (0.860 g, 3.97 mmol) (molar ratio 1:2), and C₆F₆ (1 mL, was added 1 h after the start of carbonylation) according to the typical procedure (Section 3.2b) (3 h, r.t., 15 min in methanol), gave a mixture of compounds 1a, 6′a, C₆F₅CHO, and C₆F₅CH(OMe)₂ in an 12:76:2:10 molar ratio.

e. Compound 2a (0.323 g, 1.29 mmol) and SbF₅ (1.134 g, 5.24 mmol) (molar ratio 1:4) according to the typical procedure (Section 3.2b) (3 h, r.t., 15 min in methanol), gave a mixture of compounds 1a, 2a, 6′a, C₆F₅CHO, and C₆F₅CH(OMe)₂ in a 9:4:35:2:50 molar ratio.

f. Compound 2a (0.305 g, 1.22 mmol) and SbF₅ (1.578 g, 7.29 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2b) (4.5 h, r.t., 20 min in methanol), gave a mixture of compounds 1a, 2a, 3′a, C₆F₅CHO, and C₆F₅CH(OMe)₂ in a 2:4:25:9:60 molar ratio.

2-Chloro-2-(perfluorophenyl)acetic acid (6a). White solid; mp 102–103.5 °C (CCl₄). IR (KBr) ν, cm⁻¹: 1754 (C=O), 1525, 1512 (FAR). ¹H NMR (CDCl₃): δ 11.37 (s, 1H, COOH), 5.78 (s, 1H, CHCl). ¹⁹F NMR (CDCl₃): δ −141.4 (m, 2F, F-ortho), −151.5 (tt, 1F, J_para,meta = 21, J_para,ortho = 3, F-para), −161.7 (m, 2F, F-meta). HRMS, m/z: calcd. for C₈H₂O₂Cl₁F₅ 259.9658; found 259.9655. Anal. calcd. for C₈H₂O₂Cl₁F₅: C, 36.88; H, 0.77; Cl, 13.61; F, 36.46%. Found: C, 36.77; H, 0.93; Cl, 13.31; F, 36.38%.

Methyl 2-chloro-2-(perfluorophenyl)acetate (6′a). Colorless liquid. IR (film) ν, cm⁻¹: 2962 (CH), 1770, 1747 (C=O), 1525, 1510 (FAR). ¹H NMR (CDCl₃): δ 5.70 (s, 1H, CHCl), 3.82 (s, 3H, CH₃). ¹⁹F NMR (CDCl₃): δ −141.8 (m, 2F, F-ortho), −152.4 (tt, 1F, J_para,meta = 21, J_para,ortho = 2.5, F-para), −161.2 (m, 2F, F-meta). HRMS, m/z: calcd. for C₉H₄O₂Cl₁F₅ 273.9815; found 273.9818.

3.3.5. Carbonylation of 1-(Dichloromethyl)-2,3,5,6-tetrafluoro-4-(trifluoromethyl)benzene (2d)

a. Compound 2d (0.377 g, 1.25 mmol) and SbF₅ (0.274 g, 1.27 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (1 h 45 min, r.t.), gave a mixture of compounds containing ~70% of acid 6d. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with Et₂O (3 × 5 mL). Evaporation of the solvent and sublimation (120 °C, 1 Torr) gave 0.254 g of acid 6d (yield 65%).

b. Compound 2d (0.421 g, 1.40 mmol) and SbF₅ (1.758 g, 8.12 mmol) (molar ratio 1:5.8), according to the typical procedure (Section 3.2b) (3 h 15 min, r.t., 10 min in methanol), gave a mixture of compounds containing ~80% of ester 3′d. Silica gel column chromatography (CH₂Cl₂ as the eluent) gave 0.313 g of ester 3′d (yield 64%).

2-Chloro-2-(2,3,5,6-tetrafluoro-4-(trifluoromethyl)phenyl)acetic acid (6d). White solid; mp 68–69 °C (after sublimation). IR (KBr) ν, cm⁻¹: 1743 (C=O), 1504 (FAR). ¹H NMR (CDCl₃): δ 8.60 (br.s, 1H, COOH), 5.80 (s, 1H, CHCl). ¹⁹F NMR (CDCl₃): δ −57.7 (t, 3F, J_CF3,F(3) = J_CF3,F(5) = 22, CF₃), −139.7 (m, 4F, F-2,3,5,6). HRMS, m/z: calcd. for C₉H₂O₂Cl₁F₇ 309.9626; found 309.9621. Anal. calcd. for C₉H₂O₂Cl₁F₇: C, 34.81; H, 0.65; Cl, 11.42; F, 42.82%. Found: C, 35.08; H, 1.08; Cl, 11.14; F, 42.82%.

Dimethyl 2-(2,3,5,6-tetrafluoro-4-(trifluoromethyl)phenyl)malonate (3′d). Colorless liquid. IR (film) ν, cm⁻¹: 2962 (CH), 1755 (C=O), 1500 (FAR). ¹H NMR (CDCl₃): δ 5.02 (s, 1H, CH), 3.81 (s, 6H, CH₃). ¹⁹F NMR (CDCl₃): δ −57.5 (t, 3F, J_CF3,F(3) = J_CF3,F(5) = 21.5, CF₃), −139.3 (m, 2F, F-2,6), −141.0 (m, 2F, F-3,5). HRMS, m/z: calcd. for C₁₁H₇O₄F₅ 348.0227; found 348.0222.

3.3.6. Carbonylation of (Fluoromethyl)pentafluorobenzene (7a)

a. Compound 7a (0.398 g, 1.99 mmol), SbF₅ (0.218 g, 1.01 mmol) (molar ratio 1:0.5), and C₆F₆ (0.2 mL), according to the typical procedure (Section 3.2a) (2 h, r.t.), gave a mixture of compounds containing ~15% of acid 9a along with resignification products.

b. Compound 7a (0.300 g, 1.50 mmol), SbF₅ (0.640 g, 2.96 mmol) (molar ratio 1:2), and C₆F₆ (0.2 mL), according to the typical procedure (Section 3.2a) (45 min, r.t.), gave a mixture of compounds containing ~10% of acid 9a.

c. Compound 7a (0.330 g, 1.65 mmol), SbF₅ (1.369 g, 6.32 mmol) (molar ratio 1:3.8), and C₆F₆ (0.3 mL), according to the typical procedure (Section 3.2a) (45 min, r.t.), gave a mixture of compounds containing ~75% of acid 9a.

d. Compound 7a (0.504 g, 2.52 mmol), SbF₅ (3.261 g, 15.06 mmol) (molar ratio 1:6), and C₆F₆ (0.4 mL), according to the typical procedure (Section 3.2a) (45 min, r.t.), gave a mixture of compounds containing ~90–95% of acid 9a. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with Et₂O (3 × 5 mL). Evaporation of the solvent and sublimation (100 °C, 1 Torr) gave 0.491 g of acid 9a (yield 86%).

3.3.7. Carbonylation of (Chloromethyl)pentafluorobenzene (8a)

a. Compound 8a (0.285 g, 1.32 mmol) and SbF₅ (0.148 g, 0.68 mmol) (molar ratio 1:0.5), according to the typical procedure (Section 3.2a) (2 h, r.t.), gave a mixture of compounds containing ~10% of acid 9a along with the starting compound (~10%) and resinification products.

b. Compound 8a (0.521 g, 2.41 mmol), SbF₅ (3.145 g, 14.53 mmol) (molar ratio 1:6), and (C₄F₉)₂O (0.3 mL), according to the typical procedure (Section 3.2a) (45 min, r.t.), gave a mixture of compounds containing ~90–95% of acid 9a. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with Et₂O (3 × 5 mL). Evaporation of the solvent and sublimation (100 °C, 1 Torr) gave 0.474 g of acid 9a (yield 87%).

3.3.8. Carbonylation of 1-(Fluoromethyl)-2,3,5,6-tetrafluoro-4-(trifluoromethyl)benzene (7d)

Compound 7d (0.491 g, 1.96 mmol), SbF₅ (2.594 g, 11.98 mmol) (molar ratio 1:6.1), and (C₄F₉)₂O (0.2 mL), according to the typical procedure (Section 3.2a) (1 h, r.t.), gave a complex mixture of compounds containing acid 9d (yield 6%, judging by ¹⁹F NMR with an internal standard) and acid 13 (yield 14%, ¹⁹F NMR), along with a complex mixture of other products.

3.3.9. Carbonylation of 1-(Chloromethyl)-2,3,5,6-tetrafluoro-4-(trifluoromethyl)benzene (8d)

Compound 8d (0.508 g, 1.91 mmol), SbF₅ (2.454 g, 11.33 mmol) (molar ratio 1:5.9), and (C₄F₉)₂O (0.2 mL), according to the typical procedure (Section 3.2a) (2.5 h, r.t.), gave a complex mixture of compounds. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The resulting organic layer contained (GS-MS) a mixture of dimeric and oligomeric products with M ≥ 448. The aqueous layer was acidified with HCl (pH < 1), and extracted with Et₂O (2 × 5 mL). The extract contain acid 9d (yield 6%, ¹⁹F NMR) along with a complex mixture of other products, including acid 13 (yield 4%, ¹⁹F NMR).

3.3.10. Carbonylation of 1-(Chloromethyl)-2,4,5,6-tetrafluoro-3-(trifluoromethyl)benzene (8e)

Compound 8e (0.343 g, 1.29 mmol), SbF₅ (1.686 g, 7.79 mmol) (molar ratio 1:6), and (C₄F₉)₂O (0.2 mL), according to the typical procedure (Section 3.2a) (45 min, r.t.), gave a mixture of compounds 9e and 11 in a 90:10 molar ratio. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). Evaporation of the solvent gave 0.303 g of acid 9e (yield 85%).

(2,4,5,6-Tetrafluoro-3-(trifluoromethyl)phenyl)acetic acid (9e). White solid; mp 75–76 °C (after sublimation). IR (KBr) ν, cm⁻¹: 1726 (C=O), 1510 (FAR). ¹H NMR (CDCl₃): δ 6.2 (br.s, 1H, COOH), 3.78 (s, 2H, CH₂). ¹⁹F NMR (CDCl₃): δ −57.3 (t, 3F, CF₃), −119.1 (qdddt, 1F, F-2), −128.8 (dddm, 1F, F-6), −134.1 (qddd, 1F, F-4), −163.0 (ddd, 1F, F-5); J_CF3,F(2) = J_CF3,F(4) = 22.5, J_F(2),CH2 = 1.5, J_2,4 = 3.5, J_2,5 = 11.5, J_2,6 = 4, J_4,5 = 21.5, J_4,6 = 10.5, J_5,6 = 22. HRMS, m/z: calcd. for C₉H₃O₂F₇ 276.0016; found 276.0014. Anal. calcd. for C₉H₃O₂F₇: C, 39.15; H, 1.10; F, 48.17%. Found: C, 39.70; H, 1.30; F, 48.16%.

3.3.11. Carbonylation of 1-(Chloromethyl)-3,4,5,6-tetrafluoro-2-(trifluoromethyl)benzene (8f)

Compound 8f (0.461 g, 1.73 mmol), SbF₅ (2.214 g, 10.22 mmol) (molar ratio 1:5.9), and (C₄F₉)₂O (0.2 mL), according to the typical procedure (Section 3.2a) (45 min, r.t.), gave a mixture of compounds 9f, 10, and 4,5,6,7-tetrafluorophthalide in a 92:3:5 molar ratio. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). Evaporation of the solvent gave 0.420 g of acid 9f (yield 88%).

(3,4,5,6-Tetrafluoro-2-(trifluoromethyl)phenyl)acetic acid (9f). White solid; mp 73.5–75 °C (after sublimation). IR (KBr) ν, cm⁻¹: 1726 (C=O), 1529, 1485 (FAR). ¹H NMR (acetone-d₆): δ 4.2 (br.s, 1H, COOH), 3.96 (s, 2H, CH₂). ¹⁹F NMR (acetone-d₆): δ −54.0 (d, 3F, CF₃), −138.1 (ddm, 1F, F-6), −139.0 (qddd, 1F, F-3), −149.7 (ddd, 1F, F-5), −154.9 (ddd, 1F, F-4); J_CF3,F(3) = 26, J_3,4 = 21, J_3,5 = 7.5, J_3,6 = 11.5, J_4,6 = 4.5, J_4,5 = 21, J_5,6 = 22. HRMS, m/z: calcd. for C₉H₃O₂F₇ 276.0016; found 276.0017. Anal. calcd. for C₉H₃O₂F₇: C, 39.15; H, 1.10; F, 48.17%. Found: C, 39.56; H, 1.08; F, 48.26%.

3.3.12. Carbonylation of 1-(Chloromethyl)-2,3,5,6-tetrafluoro-4-(perfluoroisopropyl)benzene (8g)

Compound 8g (0.502 g, 1.37 mmol), SbF₅ (1.825 g, 8.43 mmol) (molar ratio 1:6.1), and (C₄F₉)₂O (0.2 mL), according to the typical procedure (Section 3.2a) (1.5 h, r.t.), gave a complex mixture of compounds containing ~20% of acid 9g. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). Evaporation of the solvent and sublimation (130 °C, 1 Torr) resulted in a mixture (0.110 g) containing ~90% of acid 9g, recrystallization from hexane gave 55 mg (yield 11%) of the pure substance.

(2,3,5,6-Tetrafluoro-4-(perfluoroisopropyl)phenyl)acetic acid (9g). White solid; mp 117–118 °C (hexane). IR (KBr) ν, cm⁻¹: 1716 (C=O), 1493 (FAR). ¹H NMR (CDCl₃): δ 6.5 (br.s, 1H, COOH), 3.87 (s, 2H, CH₂). ¹⁹F NMR (CDCl₃): δ −76.4 (m, 6F, CF₃), −135.6 (br.s, 1F, Ar-F), −138.6 (br.s, 1F, Ar-F), −140.4 (br.s, 1F, Ar-F), −141.4 (br.s, 1F, Ar-F), −179.7 (m, 1F, CF(CF₃)₂). HRMS, m/z: calcd. for C₁₁H₃O₂F₁₁ 375.9952; found 375.9950.

3.3.13. Carbonylation of (Perfluoro-[1,1′-biphenyl]-4-yl)acetic acid (8h)

Compound 8h (0.498 g, 1.37 mmol), SbF₅ (1.776 g, 8.20 mmol) (molar ratio 1:6), and (C₄F₉)₂O (0.3 mL), according to the typical procedure (Section 3.2a) (2 h, r.t.), gave a complex mixture of compounds containing ~20% of starting compound 8h and ~5% acid 9h. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with Et₂O (2 × 5 mL). Evaporation of the solvent, sublimation (180 °C, 1 Torr), and recrystallization from hexane afforded 14 mg of acid 9h (yield 3%).

(Perfluoro-[1,1′-biphenyl]-4-yl)acetic acid (9h). White solid; mp 211–214 °C (after sublimation). IR (KBr) ν, cm⁻¹: 1709 (C=O), 1489, 1417 (FAR). ¹H NMR (acetone-d₆): δ 3.96 (s, 2H, CH₂), 3.3 (br.s, COOH + traces of water). ¹⁹F NMR (acetone-d₆): δ −138.0 (m, 2F, Ar-F), −139.5 (m, 2F, Ar-F), −141.5 (m, 2F, Ar-F), −151.0 (tt, 1F, F-4′, J_4′,3′ = J_4′,5′ = 20.5, J_4′,2′ = J_4′,6′ = 3), −161.4 (m, 2F, F-3′,5′). HRMS, m/z: calcd. for C₁₄H₃O₂F₉ 373.9984; found 373.9985.

3.3.14. Carbonylation of (Perfluoro-4-methylphenyl)methanol (14d)

A mixture of alcohol 14d (0.145 g, 0.58 mmol), TfOH (0.263 g, 1.75 mmol), and SbF₅ (0.379 g, 1.75 mmol) (molar ratio 1:3:3) was vigorously stirred in a 10 mL round-bottom glass flask (7 h, 60 °C) in a slow flow of CO, then poured into 5% hydrochloric acid (15 mL), extracted three times with 4 mL of a CH₂Cl₂–Et₂O mixture (3:1, v/v), and the extract was dried over MgSO₄. The resulting solution contained compounds 9d and 12 in an 88:12 molar ratio. After evaporation of the solvent, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). Evaporation of the solvent and sublimation (120 °C, 3 Torr) gave 0.104 g of acid 9d (yield 65%).

(2,3,5,6-Tetrafluoro-4-(trifluoromethyl)phenyl)acetic acid (9d). White solid; mp 77–80 °C (after sublimation). IR (KBr) ν, cm⁻¹: 1732 (C=O), 1497 (FAR). ¹H NMR (CDCl₃): δ 11.67 (br.s, 1H, COOH), 3.87 (s, 2H, CH₂). ¹⁹F NMR (CDCl₃): δ −57.4 (t, 3F, J_CF3,F(3) = J_CF3,F(5) = 21.5, CF₃), −141.2 (m, 2F, F-2,6), −141.6 (m, 2F, F-3,5). HRMS, m/z: calcd. for C₉H₃O₂F₇ 276.0016; found 276.0013.

3.3.15. Carbonylation of (Perfluoro-3-methylphenyl)methanol (14e)

Compound 14e (0.198 g, 0.80 mmol) and TfOH (0.840 g, 5.60 mmol) (molar ratio 1:7), used similarly to procedure 3.3.14 (6 h, 50 °C, extraction with CH₂Cl₂), gave a mixture of compounds containing ~95% of acid 9e. An analogous treatment gave 0.165 g of acid 9e (yield 75%).

3.3.16. Carbonylation of (Perfluoro-2-methylphenyl)methanol (14f)

Compound 14f (0.218 g, 0.88 mmol) and TfOH (0.923 g, 6.15 mmol) (molar ratio 1:7), similarly to procedure 3.3.14 (6 h, 75 °C), gave a mixture of compounds containing ~85% of acid 9f in the absence of acid 10 after hydrolysis of the reaction mixture. An analogous treatment gave 0.155 g of acid 9f (yield 64%).

3.3.17. Carbonylation of 1,4-Bis(chloromethyl)-2,3,5,6-tetrafluorobenzene (16a)

Compound 16a (0.174 g, 0.70 mmol), SbF₅ (0.974 g, 4.50 mmol) (molar ratio 1:6.4), and (C₄F₉)₂O (0.1 mL), according to the typical procedure (Section 3.2b) (2 h, r.t., 20 min in methanol), gave a complex mixture of compounds containing ~15% ester 17′a (yield 12%, ¹⁹F NMR).

Dimethyl (2,3,5,6-tetrafluoro-1,3-phenylene)diacetate (17′a) in the reaction mixture. ¹H NMR (CDCl₃): δ 3.72 (s, 6H, CH₃), 3.71 (s, 4H, CH₂).¹⁹F NMR (CDCl₃): δ −144.3 (s, 4F, F-Ar). GC-MS, m/z: calcd. for C₁₂H₁₀O₄F₄ 294; found 294.

3.3.18. Carbonylation of 1,3-Bis(chloromethyl)-2,4,5,6-tetrafluorobenzene (16b)

Compound 16b (0.272 g, 1.10 mmol), SbF₅ (1.555 g, 7.18 mmol) (molar ratio 1:6.5), and (C₄F₉)₂O (0.2 mL), according to the typical procedure (Section 3.2b) (2 h, r.t., 20 min in methanol), gave a mixture of compounds containing ~65% of ester 17′b. Silica gel column chromatography (CH₂Cl₂ as the eluent) gave 0.143 g of ester 17′b (yield 44%).

Dimethyl (2,4,5,6-tetrafluoro-1,3-phenylene)diacetate (17′b). Colorless liquid. IR (film) ν, cm⁻¹: 2958 (CH), 1747 (C=O), 1496 (FAR). ¹H NMR (CDCl₃): δ 3.68 (s, 6H, CH₃), 3.66 (s, 4H, CH₂).¹⁹F NMR (CDCl₃): δ −123.3 (d, 1F, F-2), −137.8 (d, 2F, F-4,6), −164.0 (td, 1F, F-5); J_2,5 = 11.5, J_4,5 = J_5,6 = 21.5. HRMS, m/z: calcd. for C₁₂H₁₀O₄F₄ 294.0510; found 294.0509.

3.3.19. Carbonylation of 1,2-Bis(chloromethyl)-3,4,5,6-tetrafluorobenzene (16c)

a. Compound 16c (0.287 g, 1.16 mmol), SbF₅ (1.512 g, 6.98 mmol) (molar ratio 1:6), and (C₄F₉)₂O (0.3 mL), according to the typical procedure (Section 3.2b) (1 h, r.t., 20 min in methanol), gave a mixture of compounds 17′c, 15, and 4,5,6,7-tetrafluorophthalide in an 86:10:4 molar ratio. Silica gel column chromatography (CH₂Cl₂ as the eluent) gave 0.247 g of inseparable mixture of compounds 17′c and 15 in an 89:11 molar ratio.

b. Compound 16c (0.477 g, 1.93 mmol), SbF₅ (2.896 g, 13.38 mmol) (molar ratio 1:6.9), and (C₄F₉)₂O (0.7 mL), according to the typical procedure (Section 3.2a) (2.5 h, r.t.), gave a mixture of compounds containing ~80% of acid 17c. After evaporation of Et₂O, the residue was dissolved in a saturated aqueous solution of NaHCO₃ (50 mL), acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). The aqueous layer was extracted with Et₂O (3 × 5 mL). Evaporation of the Et₂O extract, sublimation (170 °C, 1 Torr), and recrystallization from CCl₄-acetone resulted in 0.343 g of acid 17c (yield 67%).

Dimethyl (3,4,5,6-tetrafluoro-1,2-phenylene)diacetate (17′c) in the mixture with lactone 15 (17′c:15 = 89:11). Colorless liquid. IR (film) ν, cm⁻¹: 2958 (CH), 1745 (C=O), 1520, 1487 (FAR). ¹H NMR (CDCl₃): δ 3.69 (s, 4H, CH₂), 3.68 (s, 6H, CH₃).¹⁹F NMR (CDCl₃): δ −141.8 (m, 2F, F-3,6), −157.9 (m, 2F, F-4,5). HRMS, m/z: calcd. for C₁₂H₁₀O₄F₄ 294.0510; found 294.0507.

(3,4,5,6-Tetrafluoro-1,2-phenylene)diacetic acid (17c). White solid; mp 196.5–197.5 °C (CCl₄-acetone). IR (KBr) ν, cm⁻¹: 1720 (C=O), 1518, 1489 (FAR). ¹H NMR (acetone-d₆): δ 5.5 (br.s, 2H, COOH), 3.82 (s, 4H, CH₂). ¹⁹F NMR (acetone-d₆): δ −141.2 (m, 2F, F-3,6), −159.1 (m, 2F, F-4,5). HRMS, m/z: calcd. for C₁₀H₆O₄F₄ 266.0197; found 266.0193. Anal. calcd for C₁₀H₆O₄F₄: C, 45.13; H, 2.27; F, 28.55%. Found: C, 45.56; H, 2.70; F, 28.45%.

3.3.20. Carbonylation of (Fluoromethylene)bis(pentafluorobenzene) (18)

a. Compound 18 (0.375 g, 1.02 mmol), SbF₅ (0.112 g, 0.51 mmol) (molar ratio 1:0.5), and C₆F₆ (0.5 mL), according to the typical procedure (Section 3.2a) (6 h, r.t.), gave a mixture of compounds containing 45% of acid 19 along with hydrolysis products of bis(perfluophenyl)methyl cation (alcohol 40 and its ether).

b. Compound 18 (0.349 g, 0.95 mmol), SbF₅ (0.205 g, 0.95 mmol) (molar ratio 1:1), and C₆F₆ (0.5 mL), according to the typical procedure (Section 3.2a) (4.5 h, r.t.), gave a mixture of compounds containing 50% of acid 20 along with alcohol 40 and its ether. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). Evaporation of the solvent gave 0.164 g of acid 20 (yield 44%).

c. Compound 18 (0.385 g, 1.05 mmol), SbF₅ (0.800 g, 3.70 mmol) (molar ratio 1:6), and C₆F₆ (0.4 mL), according to the typical procedure (Section 3.2a) (4.5 h, r.t.), gave a mixture of compounds containing 5% of acid 20 along with alcohol 40 and its ether.

d. Compound 18 (0.222 g, 0.61 mmol) and SbF₅ (0.800 g, 3.70 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (5.5 h, r.t.), gave a mixture of compounds containing 3% of acid 20 along with alcohol 40 and its ether.

3.3.21. Carbonylation of (Chloromethylene)bis(pentafluorobenzene) (19)

a. Compound 19 (0.383 g, 1.00 mmol) and SbF₅ (0.111 g, 0.51 mmol) (molar ratio 1:0.5), according to the typical procedure (Section 3.2a) (4.5 h, r.t.), gave a mixture of compounds containing 88% of acid 20 along with perfluorodiphenylmethane (5%), perfluorobenzophenone (2%), alcohol 40, its ether, and the starting compound. After the evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). Evaporation of the solvent gave 0.335 g of acid 20 (yield 85%).

b. Compound 19 (0.468 g, 1.22 mmol) and SbF₅ (0.262 g, 1.21 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (4.5 h, r.t.), gave a mixture of compounds containing 45% of acid 20 along with perfluorodiphenylmethane (2%), perfluorobenzophenone (3%), alcohol 40, its ether and the starting compound.

c. Compound 19 (0.342 g, 0.89 mmol) and SbF₅ (1.167 g, 5.39 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (4.5 h, r.t.), gave a mixture of alcohol 40 and its ether with admixture of the starting compound, and the content of acid 20 in the mixture did not exceed 1%.

3.3.22. Carbonylation of Compound (1-Chloro-2,2,2-trifluoroethyl)pentafluorobenzene (23a)

a. Compound 23a (0.528 g, 1.86 mmol) and SbF₅ (0.200 g, 0.92 mmol) (molar ratio 1:0.5), according to the typical procedure (Section 3.2a) (1 h, r.t.), gave a mixture of compounds 23a and 24a in a 29:71 molar ratio.

b. Compound 23a (0.436 g, 1.53 mmol) and SbF₅ (0.322 g, 1.53 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (1 h, r.t.), after evaporation of the solvent and sublimation (120 °C, 3 Torr), afforded 0.416 g of acid 24a (yield 92%) with a 3% admixture of acid 9a.

c. Compound 23a (0.567 g, 2.00 mmol) and SbF₅ (0.428 g, 1.98 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2b) (1.5 h, r.t., 15 min in methanol), after washing of the extract with a saturated aqueous solution of NaHCO₃ (30 mL) and evaporation of the solvent gave 0.556 g of ester 24′a (yield 90%).

d. Compound 23a (0.358 g, 1.35 mmol) and SbF₅ (1.758 g, 8.12 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (0.5 h, r.t.), after evaporation of the solvent and sublimation (120 °C, 1 Torr), afforded 0.380 g of acid 24a (yield 96%) with a 2% admixture of acid 9a.

e. Compound 23a (0.347 g, 1.22 mmol) and SbF₅ (1.560 g, 7.21 mmol) (molar ratio 1:5.9), according to the typical procedure (Section 3.2a) (5 h, 70 °C), gave a mixture of compounds 24a, 25a, 3a, 9a in the following molar ratios: 28:25:42:5 (2.5 h after extraction, r.t.); 28:2:38:32 (24 h after extraction, r.t.).

f. Compound 23a (0.362 g, 1.27 mmol) and SbF₅ (1.603 g, 7.40 mmol) (molar ratio 1:5.8), according to the typical procedure (Section 3.2b) (7 h, 70 °C, 15 min in methanol) gave a mixture of compounds which did not contain acid 25a or its methyl ester. The main products in the mixture were compounds 28′, 3′a, 24′a, and 24a in a 53:21:13:13 molar ratio with total content ~90%. The extract was washed with a saturated aqueous solution of NaHCO₃ (30 mL), and silica gel column chromatography (CCl₄–CH₂Cl₂ [1:1, v/v] as the eluent) gave 88 mg of compound 28′ (yield 22%).

Perfluoro-2-phenylpropenoic acid (25a) was in the mixture with acids 24a, 3a, 9a. ¹⁹F NMR (CDCl₃): δ −58.4 (dt, 1F, F-3A), −59.1 (dt, 1F, F-3B), −138.5 (m, 2F, F-ortho), −152.3 (tt, 1F, F-para), −162.3 (m, 2F, F-meta); J_3Z,3E = 38, J_3Z,ortho = 1.5, J_3E,ortho = 6, J_para,meta = 21, J_para,ortho = 2.5.

Methyl 3,3-difluoro-3-methoxy-2-perfluorophenylpropanoate (28′). Colorless liquid. IR (film) ν, cm⁻¹: 2964 (CH), 1770 (C=O), 1525, 1508 (FAR). ¹H NMR (CDCl₃): δ 4.56 (t, 1H, J_H(2),F(3) = 8, H-2), 3.76 (s, 3H, CO₂CH₃), 3.57 (s, 3H, CF₂OCH₃). ¹⁹F NMR (CDCl₃): δ −77.6 (dq, 1F, F_A-3), −78.0 (dq, 1F, F_B-3), −140.4 (m, 2F, F-ortho), −153.9 (tt, 1F, F-para), −162.7 (m, 2F, F-meta); J_3A,3B = 141, J_3,ortho = J_H(2),F(3) = 8, J_para,meta = 21, J_para,ortho = 2.5. HRMS, m/z: calcd. for C₁₁H₇O₃F₇ 320.0278; found 320.0278.

3.3.23. Carbonylation of (1,2,2,3,3,3-Hexafluoropropyl)pentafluorobenzene (22b)

a. Compound 22b (0.376 g, 1.18 mmol) and SbF₅ (0.253 g, 1.17 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (0.5 h, r.t.), gave a mixture of compounds 24b, 25b (E:Z = 55:45), and 26b in an 86:9:5 molar ratio. After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The resulting solution contained mainly compound 26b. The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with Et₂O (3 × 5 mL). Evaporation of the solvent and sublimation (120 °C, 3 Torr) resulted in a mixture (0.345 g) of acids 24b and 25b in a 90:10 molar ratio.

b. Compound 22b (0.276 g, 0.87 mmol) and SbF₅ (0.388 g, 1.79 mmol) (molar ratio 1:2), according to the typical procedure (Section 3.2a) (0.5 h, r.t.), gave a mixture of compounds 24b, 25b (E:Z = 60:40), and 26b in a 90:9:1 molar ratio.

c. Compound 22b (0.210 g, 0.66 mmol) and SbF₅ (0.583 g, 2.69 mmol) (molar ratio 1:4), according to the typical procedure (Section 3.2a) (0.5 h, r.t.), gave a mixture of compounds 24b and 25b (E:Z = 60:40) in a 95:5 molar ratio.

d. Compound 22b (0.378 g, 1.19 mmol) and SbF₅ (1.556 g, 7.19 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (0.5 h, r.t.), gave a mixture of compounds 24b and 25b (E:Z = 60:40) in a 95:5 molar ratio. Evaporation of the solvent, sublimation (90 °C, 1 Torr), and recrystallization from hexane resulted in 0.333 g of acid 24b (yield 81%).

e. Compound 22b (0.359 g, 1.13 mmol) and SbF₅ (1.458 g, 6.73 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2b) (6 h, 70 °C, 10 min in methanol), gave a mixture of compounds 25′b (E:Z = 85:15) and 25b (E:Z = 60:40) in a 80:20 molar ratio with total content ~90%. Methyl ester 24′b was not detected in the mixture. Silica gel column chromatography (CCl₄–CH₂Cl₂ [1:1, v/v] as the eluent) gave 0.263 g of compound 25′b (yield 69%).

1,1,1-Trifluoro-3-(perfluorophenyl)propan-2-one (26b) in the mixture.¹H NMR (CDCl₃): δ 4.10 (s, 2H, CH₂). ¹⁹F NMR (CDCl₃): δ −79.9 (s, 3F, CF₃), −143.2 (m, 2F, F-ortho), −153.8 (t, 1F, J_para,meta = 20.5, F-para), −162.1 (m, 2F, F-meta). GC-MS, m/z: calcd. for C₉H₂O₁F₈ 278; found 278.

3.3.24. Carbonylation of (1-Chloro-2,2,3,3,3-pentafluoropropyl)pentafluorobenzene (23b) (With Admixture of P-chloroderivative 45, See Procedure 3.4.4e)

a. Compound 23b (0.360 g, 1.08 mmol) and SbF₅ (0.238 g, 1.10 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (1 h, r.t.), gave a mixture of compounds 24b, 25b, and 26b in an 89:5:6 molar ratio (with admixtures of the corresponding p-chloroderivatives).

b. Compound 23b (0.335 g, 1.00 mmol) and SbF₅ (1.295 g, 5.98 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (1 h, r.t.), gave a mixture of compounds 24b and 25b (E:Z = 60:40) in a 95:5 molar ratio (with admixtures of the corresponding p-chloroderivatives). Similar procedure with a reaction time of 5 h gave a mixture of compounds 24b and 25b (E:Z = 60:40) in a 91:9 molar ratio.

c. Compound 23b (0.358 g, 1.07 mmol) and SbF₅ (1.390 g, 6.42 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (1 h, 70 °C), gave a mixture of compounds 24b, 25b, and 26b in the 36:60:4 molar ratio (with admixtures of the corresponding p-chloroderivatives). Similar procedure with a reaction time of 5 h gave a mixture of compounds 24a, 25b, and 26b in a 2:92:6 molar ratio.

3.3.25. Carbonylation of 1-Chloro-2,2,3,3,4,4,5,6,7,8-decafluorotetralin (23c) (With Admixture of Isomer 47, See Procedure 3.4.4f)

a. Compound 23c (0.346 g, 1.00 mmol) and SbF₅ (0.212 g, 0.98 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (1 h, r.t.), gave a mixture of compounds 24c, 25c, and 26c in an 81:7:12 molar ratio (with 8% of admixtures of the corresponding 6-chloroderivatives). After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with Et₂O (3 × 5 mL). Evaporation of the solvent, sublimation (100 °C, 1 Torr), and recrystallization from hexane resulted in 0.210 g of acid 24c (yield 59%). The product contained 3% of the 6-chloroderivative 48.

b. Compound 23c (0.380 g, 1.10 mmol) and SbF₅ (1.413 g, 6.53 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (1 h, r.t.), gave a mixture of compounds 24c and 25c in an 87:13 molar ratio (with 8% admixtures of 6-chloroderivatives 48 and 49), the content of compound 26c in the mixture did not exceed 2%.

c. Compound 23c (0.356 g, 1.03 mmol) and SbF₅ (1.343 g, 6.20 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (1 h, 70 °C), gave a mixture of compounds 25c and 26c in a 94:6 molar ratio (with 6% admixtures of the corresponding 6-chloroderivatives). After evaporation of Et₂O, the residue was dissolved in CH₂Cl₂ (10 mL) and washed with a saturated aqueous solution of NaHCO₃ (30 mL). The aqueous layer was separated, acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (3 × 5 mL). Evaporation of the solvent, sublimation (110 °C, 1 Torr), and recrystallization from hexane resulted in 0.234 g of acid 25c (yield 68%), the product contained 3% of 6-chloroderivative 49.

Perfluoro-3,4-dihydronaphthalene-1-carboxylic acid (25c). White solid; mp 102.5–104.5 °C (hexane). IR (KBr) ν, cm⁻¹: 1732 (C=O), 1520, 1497 (FAR). ¹H NMR (CDCl₃): δ 10.08 (s, 1H, CO₂H). ¹⁹F NMR (CDCl₃): δ −120.0 (tm, 1F, F-3), −120.5 (dm, 2F, F-4), −130.9 (m, 2F, F-3), −133.9 (dddd, 1F, F-8), −136.5 (tdddd, 1F, F-5), −147.0 (tdq, 1F, F-7), −149.2 (dddd, 1F, F-6); J_2,3 = 18, J_2,5 = 2, J_2,6 = 7, J_2,7 = 2, J_2,8 = 6, J_5,6 = 20.5, J_5,7 = 9, J_5,8 = 11.5, J_6,7 = 20, J_6,8 = 6, J_7,8 = 20. HRMS, m/z: calcd. for C₁₁H₁O₂F₉ 335.9829; found 335.9827. Anal. calcd. for C₁₁H₁O₂F₉: C, 39.31; H, 0.30; F, 50.87%. Found: C, 38.83; H, 0.50; F, 50.80%.

3.3.26. Carbonylation of 1,2,2,3,3,4,5,6,7-Nonafluoroindan (22d)

a. Compound 22d (0.422 g, 1.51 mmol) and SbF₅ (0.314 g, 1.45 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (0.5 h, r.t.), gave a mixture of compounds containing ~95% of acid 24d. The content of acid 25d in the mixture did not exceed 2%. Evaporation of the solvent, sublimation (105 °C, 1 Torr), and recrystallization from CCl₄-hexane resulted in 0.411 g of acid 24d (yield 79%).

b. Compound 22d (0.676 g, 2.41 mmol) and SbF₅ (3.083 g, 14.24 mmol) (molar ratio 1:5.9), according to the typical procedure (Section 3.2b) (7 h, 70 °C, 20 min in methanol), gave a mixture of compounds 24′d, 29′, 30, and 31 in a 6:51:35:8. Silica gel column chromatography (CH₂Cl₂ as the eluent) gave 0.138 g of compounds 29′ (yield 18%).

Dimethyl 2,4,5,6,7-pentafluoro-1H-indene-1,3-dicarboxylate (29′). Colorless liquid. IR (film) ν, cm⁻¹: 2960 (CH), 1741 (C=O), 1512, 1493 (FAR). ¹H NMR (CDCl₃): δ 4.69 (s, 1H, H-1), 3.90 (s, 3H, CO₂CH₃-3), 3.79 (s, 3H, CO₂CH₃-1). ¹⁹F NMR (CDCl₃): δ −101.7 (dd, 1F, F-2), −139.9 (dddd, 1F, F-4), −142.0 (ddm, 1F, F-7), −154.5 (ddd, 1F, F-5), −157.9 (dddd, 1F, F-6); J_2,4 = 5, J_2,6 = 14, J_4,5 = 20, J_4,6 = 2.5, J_4,7 = 15, J_5,6 = 19, J_5,7 = 3.5, J_6,7 = 21. HRMS, m/z: calcd. for C₁₃H₇O₄F₅ 322.0259; found 322.0256.

3.3.27. Carbonylation of 1-Chloro-2,2,3,3,4,5,6,7-octafluoroindan (23d)

a. Compound 23d (0.422 g, 1.42 mmol) and SbF₅ (0.310 g, 1.43 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2a) (1 h, r.t.), gave a mixture of compounds containing 50% of acid 24d and 9% of starting compound 23d along with their derivatives with moieties C=O, CFCl, CCl₂ instead of CF₂ in the benzylic position.

b. Compound 23d (0.358 g, 1.30 mmol) and SbF₅ (1.693 g, 7.82 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2a) (0.5 h, r.t.), gave a mixture of compounds containing 50% of acid 24d along with 3-X-2,2,4,5,6,7-hexafluoroindan-1-ones (X = COOH, Cl, F), the content of acid 25d in the mixture did not exceed 2%.

3.3.28. Carbonylation of 1,4-Dichloro-2,2,3,3,5,6,7,8-octafluorotetralin (36) (With Admixtures of Isomeric Compounds, See Procedure 3.4.4h)

a. Compound 36 (0.395 g, 1.14 mmol) and SbF₅ (0.242 g, 1.12 mmol) (molar ratio 1:1), according to the typical procedure (Section 3.2b) (0.5 h, r.t., 26 h in methanol), gave a mixture of compounds 36, 37′, 38′, 39′, and dimethyl 1,2,2,3,3,5,6,7,8-nonafluorotetralin-1,4-dicarboxylate in a 7:66:10:1:16 molar ratio (with admixtures of the corresponding chloroderivatives). After evaporation of a solvent, the residue was dissolved in a solution of NEt₃ (0.770 g) in dry CH₂Cl₂ (8 mL). The solution was kept at r.t. for 1 h, washed with 5% hydrochloric acid (20 mL), and dried over MgSO₄. The mixture of compounds in the solution contained 38′, 39′, and 1,4-dichlorohexafluoronaphthalene in a 76:17:7 molar ratio. Silica gel column chromatography (CCl₄–CH₂Cl₂ [1:1, v/v] as the eluent) gave 0.268 g of compound 38′ (yield 71%). The product contained 9% of the 6- and 7-chloroderivatives.

b. Compound 36 (0.316 g, 0.92 mmol) and SbF₅ (1.200 g, 5.54 mmol) (molar ratio 1:6), according to the typical procedure (Section 3.2b) (3 h, r.t., 28 h in methanol), gave a mixture of compounds containing (GC-MS) 73% of ester 39′, 9% of its 6-chloroderivative 53′, and 3% of ester 38′. Silica gel column chromatography (CCl₄–CH₂Cl₂ [1:1, v/v] as the eluent) gave 0.220 g of compound 39′ (yield 68%), the product contained 8% of the 6-chloroderivative 53′.

Methyl 4-chloro-2,2,3,3,5,6,7,8-octafluorotetralin-1-carboxylate (37′) (isomers A:B = 83:17) in the mixture with other products. Isomer A. ¹⁹F NMR (CDCl₃): −112.8 (dm, 1F, J_A,B = 264, CF₂-F_A), −116.6 (dm, 1F, J_A,B = 263, CF₂-F_A), −116.8 (dm, 1F, J_A,B = 264, CF₂-F_B), −128.2 (dm, 1F, J_A,B = 263, CF₂-F_B), −136.5 (dddd, 1F, F-8), −138.8 (ddd, 1F, F-5), −151.9 (ddd, 1F, F-7), −153.3 (dddd, 1F, F-6); J_5,6 = 20.5, J_5,7 = 5.5, J_5,8 = 11.5, J_6,7 = 20.5, J_6,8 = 5, J_F(6),H = 2, J_7,8 = 20.5, J_F(8),H = 1.5.

Isomer B. ¹⁹F NMR (CDCl₃): −115.5 (dm, 1F, J_A,B = 265, CF₂-F_A), −115.9 ÷ −117.4 (2F, CF₂-F_A,F_B), −127.3 (dm, 1F, J_A,B = 265, CF₂-F_B), −137.2 (ddd, 1F, F-5), −138.7 (dddd, 1F, F-8), −152.1 (ddd, 1F, F-7), −153.2 (ddd, 1F, F-6); J_5,6 = 20.5, J_5,7 = 6, J_5,8 = 11.5, J_6,7 = 20.5, J_6,8 = 5, J_7,8 = 20.5, J_F(8),H = 1.5.

Methyl perfluoro-4-chloro-1-naphthoate (38′). White solid; mp 61–62.5 °C (hexane). IR (KBr) ν, cm⁻¹: 2962 (CH), 1749 (C=O), 1527, 1508, 1465, 1450 (FAR). ¹H NMR (CDCl₃): δ 4.02 (s, 3H, CH₃). ¹⁹F NMR (CDCl₃): δ −129.7 (m, 1F, F-3), −133.4 (m, 1F, F-2), −142.3 (m, 2F, F-5,8), −154.4 (m, 2F, F-6,7). HRMS, m/z: calcd. for C₁₂H₃O₂Cl₁F₆ 327.9720; found 327.9718.

Dimethyl perfluoro-6-chloronaphthalene-1,4-dicarboxylate (53′) in a mixture with compound 39′ (39′:53′ = 92:8). ¹H NMR (CDCl₃): δ 4.01 (s, 6H, CH₃). ¹⁹F NMR (CDCl₃): δ −118.7 (ddd, 1F, F-5), −133.4 (dddd, 1F, F-2), −134.9 (dddd, 1F, F-3), −136.5 (ddd, 1F, F-7), −144.0 (dddd, 1F, F-8); J_2,3 = 21.5, J_2,5 = 4, J_2,7 = 2, J_2,8 = 6, J_3,5 = 5.5, J_3,7 = 8.5, J_3,8 = 4, J_5,8 = 15.5, J_7,8 = 18. HRMS, m/z: calcd. for C₁₄H₆O₂Cl₁F₅ 367.9869; found 367.9865.

3.4. Synthesis of the Starting Compounds

3.4.1. Synthesis of Alcohols 14d–h

a. A mixture of acid 42d (1.460 g, 5.57 mmol), SOCl₂ (1.326 g, 11.14 mmol), and 4 drops of DMF was heated (5.5 h, 70–75 °C), the excess of SOCl₂ was distilled off, the residue was dissolved in Et₂O (6 mL) and added dropwise to a mixture of LiBH₄ (0.268 g, 12.29 mmol) and Et₂O (6 mL) cooled on ice. The obtained mixture was stirred at r.t. for 15 min, poured into 5% hydrochloric acid (10 mL), the organic layer combined with Et₂O extract (10 mL) was washed with a 10% aqueous solution of K₂CO₃ (30 mL) and dried over MgSO₄. Evaporation of the solvent and distillation in vacuum (120 °C, 6 Torr) gave 1.016 g of alcohol 14d (yield 74%).

b. An analogous procedure for acid 42e (2.00 g, 7.63 mmol), SOCl₂ (1.817 g, 15.27 mmol), and LiBH₄ (0.366 g, 16.79 mmol) afforded 1.600 g of alcohol 14e (yield 85%).

c. An analogous procedure for acid 42f (1.414 g, 5.39 mmol), SOCl₂ (1.284 g, 8.59 mmol), and LiBH₄ (0.259 g, 11.88 mmol) afforded 0.975 g of alcohol 14f (yield 73%).

d. An analogous procedure for acid 42g (3.440 g, 9.50 mmol), SOCl₂ (3.28 g, 27.56 mmol), and LiBH₄ (0.470 g, 21.56 mmol) afforded 2.963 g of alcohol 14g (yield 90%).

e. An analogous procedure for acid 42h (3.450 g, 9.50 mmol), SOCl₂ (4.92 g, 41.34 mmol), and LiBH₄ (0.490 g, 22.48 mmol) with subsequent sublimation (110 °C, 1 Torr) of the product afforded 2.970 g of alcohol 14h (yield 90%).

(Perfluoro-4-methylphenyl)methanol (14d). White solid; mp 41.5–42.5 °C (after distillation). IR (KBr) ν, cm⁻¹: 3330 (OH), 1497 (FAR). ¹H NMR (CDCl₃): δ 4.85 (s, 2H, CH₂), 2.04 (s, 1H, OH). ¹⁹F NMR (CDCl₃): δ −57.6 (t, 3F, CF₃ J_CF3,F(3) = J_CF3,F(5) = 22), −141.4 (m, 2F, F-3,5), −143.6 (m, 2F, F-2,6). HRMS, m/z: calcd. for C₈H₃O₁F₇ 248.0067; found 248.0064.

(Perfluoro-3-methylphenyl)methanol (14e). Colorless liquid. IR (film) ν, cm⁻¹: 3338 (OH), 1506 (FAR). ¹H NMR (CDCl₃): δ 4.75 (s, 2H, CH₂), 2.59 (s, 1H, OH). ¹⁹F NMR (CDCl₃): δ −57.3 (t, 3F, CF₃), −121.2 (qdddt, 1F, F-2), −130.9 (dddm, 1F, F-6), −133.5 (qddd, 1F, F-4), −163.0 (ddd, 1F, F-5); J_CF3,F(2) = J_CF3,F(4) = 22.5, J_2,4 = 3, J_2,5 = 11.5, J_2,6 = 5, J_4,5 = 21, J_4,6 = 10.5, J_5,6 = 21.5, J_CH2,F(2) = 2. HRMS, m/z: calcd. For [M-H]⁺ C₈H₂O₁F₇ 246.9986; found 246.9985.

(Perfluoro-2-methylphenyl)methanol (14f). Colorless liquid. IR (film) ν, cm⁻¹: 3360 (OH), 1527, 1483 (FAR). ¹H NMR (CDCl₃): δ 4.80 (s, 2H, CH₂), 2.49 (s, 1H, OH). ¹⁹F NMR (CDCl₃): δ −55.2 (d, 3F, CF₃), −138.3 (qddd, 1F, F-3), −140.9 (dddt, 1F, F-6), −149.0 (ddd, 1F, F-5), −153.4 (ddd, 1F, F-5); J_CF3,F(3) = 28.5, J_3,4 = 20.5, J_3,5 = 8, J_3,6 = 12, J_4,5 = 20, J_4,6 = 5, J_5,6 = 21.5, J_CH2,F(6) = 2. HRMS, m/z: calcd. for C₈H₃O₁F₇ 248.0067; found 248.0066.

(2,3,5,6-Tetrafluoro-4-(perfluoroisopropyl)phenyl)methanol (14g). Colorless liquid. IR (film) ν, cm⁻¹: 3356 (OH), 1489 (FAR). ¹H NMR (CDCl₃): δ 4.86 (d, 2H, CH₂, J_CH2,OH = 6), 2.18 (t, 1H, OH, J_CH2,OH = 6). ¹⁹F NMR (CDCl₃): δ −76.4 (m, 6F, CF₃), −135.3 (br.s, 1F, Ar-F), −138.3 (br.s, 1F, Ar-F), −142.6 (br.s, 1F, Ar-F), −143.7 (br.s, 1F, Ar-F), −179.8 (m, 1F, CF(CF₃)₂). HRMS, m/z: calcd. for C₁₀H₃OF₁₁ 348.0003; found 347.9999.

(Perfluoro-[1,1′-biphenyl]-4-yl)methanol (14h). White solid; mp 73–74 °C (after sublimation). IR (KBr) ν, cm⁻¹: 3292 (OH), 1535, 1508, 1479 (FAR). ¹H NMR (CDCl₃): δ 4.89 (s, 2H, CH₂), 2.15 (s, 1H, OH). ¹⁹F NMR (CDCl₃): δ −138.5 (m, 2F, Ar-F), −139.4 (m, 2F, Ar-F), −144.7 (m, 2F, Ar-F), −151.3 (tt, 1F, F-4′, J_4′,3′ = J_4′,5′ = 21, J_4′,2′ = J_4′,6′ = 3), −161.7 (m, 2F, F-3′,5′). HRMS, m/z: calcd. for C₁₃H₃OF₉ 346.0035; found 346.0032.

3.4.2. Synthesis of Chloroderivatives 8a,d–g

a. A mixture of alcohol 14a (2.950 g, 14.90 mmol) and SOCl₂ (3.608 g, 30.32 mmol) was heated (2 h, 75 °C), the excess of SOCl₂ was distilled off, distillation in vacuum (110 °C, 55 Torr) gave 2.940 g of compound 8a (yield 91%).

b. A mixture of alcohol 14d (1.761 g, 5.26 mmol) and SOCl₂ (1.640 g, 15.16 mmol) was heated (1.5 h, 75 °C), the excess of SOCl₂ was distilled off, and distillation in vacuum (110 °C, 20 Torr) gave 1.633 g of compound 8d (yield 86%).

c. A mixture of alcohol 14e (1.12 g, 4.52 mmol) and SOCl₂ (1.148 g, 9.64 mmol) was heated (1.5 h, 75 °C), poured into ice water (10 mL), extracted with CH₂Cl₂ (2 × 2 mL), and dried over MgSO₄. Evaporation of the solvent and distillation in vacuum (115 °C, 30 Torr) gave 1.139 g of compound 8e (yield 94%).

d. A mixture of alcohol 14f (2.488 g, 10.03 mmol) and SOCl₂ (6.560 g, 55.13 mmol) was heated (4.5 h, 75 °C), poured into ice water (40 mL), extracted with CH₂Cl₂ (2 × 4 mL), and dried over MgSO₄. Evaporation of the solvent and distillation in vacuum (115 °C, 42 Torr) gave 2.476 g of compound 8f (yield 93%).

e. A mixture of alcohol 14g (1.829 g, 7.10 mmol) and SOCl₂ (1.804 g, 15.16 mmol) was heated (1.5 h, 75 °C), the excess of SOCl₂ was distilled off, and distillation in vacuum (120 °C, 17 Torr) gave 1.798 g of compound 8g (yield 93%).

1-(Chloromethyl)-2,3,5,6-tetrafluoro-4-(trifluoromethyl)benzene (8d). Colorless liquid. ¹H NMR (CDCl₃): δ 4.82 (s, CH₂). ¹⁹F NMR (CDCl₃): δ −57.5 (t, 3F, CF₃ J_CF3,F(3) = J_CF3,F(5) = 22), −140.7 (m, 2F, F-3,5), −141.7 (m, 2F, F-2,6). HRMS, m/z: calcd. for C₈H₂ClF₇ 265.9728; found 265.9724.

1-(Chloromethyl)-2,4,5,6-tetrafluoro-3-(trifluoromethyl)benzene (8e). Colorless liquid. ¹H NMR (CDCl₃): δ 4.62 (t, CH₂, J_CH2,F(2) = J_CH2,F(6) = 1.5). ¹⁹F NMR (CDCl₃): δ −57.3 (td, 3F, CF₃), −119.5 (qdddt, 1F, F-2), −129.2 (dddtq, 1F, F-6), −131.9 (qddd, 1F, F-4), −162.2 (td, 1F, F-5); J_CF3,F(2) = J_CF3,F(4) = 22.5, J_CF3,F(6) = 1.5, J_2,4 = 2.5, J_2,5 = 11.5, J_2,6 = 3.5, J_4,5 = 21.5, J_4,6 = 11.5, J_5,6 = 21.5, J_CH2,F(2) = J_CH2,F(6) = 1.5. HRMS, m/z: calcd. for C₈H₂ClF₇ 265.9728; found 265.9732.

1-(Chloromethyl)-3,4,5,6-tetrafluoro-2-(trifluoromethyl)benzene (8f). Colorless liquid. ¹H NMR (CDCl₃): δ 4.71 (d, CH₂, J_CH2,F(2) = 2). ¹⁹F NMR (CDCl₃): δ −55.6 (d, 3F, CF₃), −137.6 (qddd, 1F, F-3), −138.7 (dddt, 1F, F-6), −148.5 (ddd, 1F, F-5), −152.0 (ddd, 1F, F-5); J_CF3,F(3) = 28, J_3,4 = 21, J_3,5 = 8, J_3,6 = 11.5, J_4,5 = 20.5, J_4,6 = 5.5, J_5,6 = 21.5, J_CH2,F(6) = 2. HRMS, m/z: calcd. for C₈H₂ClF₇ 265.9728; found 265.9725.

1-(Chloromethyl)-2,3,5,6-tetrafluoro-4-(perfluoroisopropyl)benzene (8g). Colorless liquid. ¹H NMR (CDCl₃): δ 4.66 (s, CH₂). ¹⁹F NMR (CDCl₃): δ −76.3 (m, 6F, CF₃), −134.7 (br.s, 1F, Ar-F), −137.7 (br.s, 1F, Ar-F), −141.8 (br.s, 1F, Ar-F), −142.0 (br.s, 1F, Ar-F), −179.7 (m, 1F, CF(CF₃)₂). HRMS, m/z: calcd. for C₁₀H₂ClF₁₁ 365.9664; found 365.9662.

3.4.3. Reaction of (2,3,4,5-Tetrafluoro-6-(hydroxymethyl)phenyl)methanol (43) with SOCl₂

A mixture of diol 43 (0.262 g, 1.25 mmol) and SOCl₂ (0.820 g, 6.89 mmol) was heated (1 h 40 min, 75 °C), the excess of SOCl₂ was distilled off, the resulting mixture contained compounds 44 and 16c in an 86:14 molar ratio. Sublimation (110 °C, 1 Torr) and recrystallization from hexane resulted in 0.189 g of compound 44 (yield 59%).

1,5-Dihydrobenzo[e][1,3,2]dioxathiepine 3-oxide (44). White solid; mp 76–77 °C (hexane). ¹H NMR (CDCl₃): δ 5.80 (d, 2H, CH₂, J_A,B = 15), 4.97 (d, 2H, CH₂, J_A,B = 15). ¹⁹F NMR (CDCl₃): δ −143.0 (m, 2F, F-3,6), −155.5 (m, 2F, F-4,5). HRMS, m/z: calcd. for C₈H₄O₃F₄S 255.9812; found 255.9815. Anal. calcd. for C₈H₄O₃F₄S: C, 37.51; H, 1.57; F, 29.67%; S, 12.52%. Found: C, 38.19; H, 2.04; F, 29.88%; S, 12.44%.

3.4.4. Synthesis of Chloroderivatives 8h, 16c, 19, 23a–d, and 36

a. A mixture of alcohol 14h (0.985 g, 2.85 mmol) and PCl₅ (0.940 g, 4.51 mmol) was sealed in a glass tube (before the start of the reaction) and heated (3 h, 100 °C), poured into ice water (10 mL), extracted with CH₂Cl₂ (2 × 5 mL), and dried over MgSO₄. Evaporation of the solvent and sublimation (100 °C, 1 Torr) gave 1.011 g of compound 8h (yield 97%).

b. A mixture of diol 43 (2.000 g, 9.52 mmol) and PCl₅ (5.237 g, 25.12 mmol) was sealed in a glass tube (before the start of the reaction) and heated (3 h 40 min, 100 °C), poured into ice water (50 mL), extracted with CH₂Cl₂ (2 × 10 mL), and dried over MgSO₄. Evaporation of the solvent and distillation in vacuum (130 °C, 15 Torr) gave 2.136 g of compound 16c (yield 91%).

c. A mixture of alcohol 40 (4.06 g, 11.15 mmol) and PCl₅ (2.95 g, 14.15 mmol) was sealed in a glass tube (before the start of the reaction) and heated (3.5 h, 100 °C), poured into ice water (40 mL), extracted with CH₂Cl₂ (2 × 5 mL), and dried over MgSO₄. Evaporation of the solvent gave 4.18 g of compound 19 (yield 98%).

d. A mixture of alcohol 41a (5.96 g, 22.4 mmol) and PCl₅ (6.96 g, 33.4 mmol) was sealed in a glass tube (before the start of the reaction) and heated (5.5 h, 100 °C), poured into ice water (50 mL), extracted with CH₂Cl₂ (2 × 5 mL), and dried over MgSO₄. The resulting mixture of products contained ~90% of compound 23a. Evaporation of the solvent and distillation in vacuum (120 °C, 40 Torr) gave 5.40 g of compound 23a (yield 85%).

e. A mixture of alcohol 41b (4.14 g, 13.1 mmol) and PCl₅ (4.11 g, 19.7 mmol) was sealed in a glass tube (before the start of the reaction) and heated (10 h, 100 °C), poured into ice water (50 mL), extracted with CH₂Cl₂ (2 × 5 mL), and dried over MgSO₄. The resulting mixture of products contained ~90% of compounds 23b and 45 in a 76:24 molar ratio. Evaporation of the solvent and distillation in vacuum (110 °C, 25–15 Torr) gave 3.83 g (yield 87%) of a mixture of compounds 23b and 45 in a 79:21 molar ratio. This mixture was used in the carbonylation experiments (Section 3.3.24).

f. A mixture of alcohol 41c (3.00 g, 9.15 mmol) and PCl₅ (2.53 g, 12.13 mmol) was sealed in a glass tube (before the start of the reaction) and heated (5.5 h, 100 °C), poured into ice water (40 mL), extracted with CH₂Cl₂ (2 × 5 mL), and dried over MgSO₄. The resulting mixture of products contained ~90% of compounds 23c and 47 in a 91:9 molar ratio. Steam distillation and subsequent distillation in vacuum (135 °C, 22 Torr) gave 2.51 g (yield 79%) of a mixture of compounds 23c and 47 in a 92:8 molar ratio. The content of a dichloroderivative did not exceed 1% (GC-MS). This mixture was used in the carbonylation experiments (Section 3.3.25).

g. A mixture of alcohol 41d (6.46 g, 23.2 mmol) and PCl₅ (7.33 g, 35.2 mmol) was sealed in a tube (before the start of reaction) and heated (6 h, 100 °C), poured into ice water (100 mL), extracted with CH₂Cl₂ (2 × 10 mL), and dried over MgSO₄. The resulting mixture of products contained ~70% of compounds 23d, along with a number of nonvolatile admixtures containing a tetrafluorosubstituted aromatic ring which were separated by steam distillation. Distillation in vacuum (120 °C, 45 Torr) gave 4.61 g (yield 67%) of compounds 23d.

h. A mixture of alcohol 51 (2.5 g, 8.11 mmol) and PCl₅ (4.30 g, 20.62 mmol) was sealed in a glass tube (before the start of the reaction) and heated (10 h, 100 °C), poured into ice water (40 mL), extracted with CH₂Cl₂ (2 × 5 mL), and dried over MgSO₄. The resulting mixture of products contained ~70% of compounds 36. Steam distillation and subsequent distillation in vacuum (150 °C, 15 Torr) gave 1.88 g (yield 67%) of a mixture containing (NMR ¹⁹F, GC-MS) ~90% of compounds 36 (isomers A:B = 64:36) along with isomeric compounds. The content of trichloroderivatives did not exceed 3% (GC-MS). This mixture was used in the carbonylation experiments (Section 3.3.28).

4-(Chloromethyl)nonafluoro-1,1′-biphenyl (8h). White solid; mp 65.5–66 °C (after sublimation).¹H NMR (CDCl₃): δ 4.71 (s, CH₂). ¹⁹F NMR (CDCl₃): δ −138.3 (m, 2F, Ar-F), −138.7 (m, 2F, Ar-F), −142.9 (m, 2F, Ar-F), −150.9 (tt, 1F, F-4′, J_4′,3′ = J_4′,5′ = 21, J_4′,2′ = J_4′,6′ = 3), −161.5 (m, 2F, F-3′,5′). HRMS, m/z: calcd. for C₁₃H₂ClF₉ 363.9696; found 363.9694.

1,2-Bis(chloromethyl)-3,4,5,6-tetrafluorobenzene (16c). Colorless liquid. ¹H NMR (CDCl₃): δ 4.73 (s, CH₂).¹⁹F NMR (CDCl₃): δ −141.8 (m, 2F, F-3,6), −154.2 (m, 2F, F-4,5). HRMS, m/z: calcd. for C₈H₄Cl₂F₄ 245.9621; found 245.9620.

(1-Chloro-2,2,2-trifluoroethyl)pentafluorobenzene (23a). Colorless liquid. ¹H NMR (CDCl₃): δ 5.50 (qt, 1H, J_H,CF3 = 7, J_H,F(ortho) = 1, CHCl). ¹⁹F NMR (CDCl₃): δ −73.8 (td, 3F, J_CF3,F(ortho) = 10, J_H,CF3 = 7, CF₃), ~−138.4 (br.s, 2F, F-ortho), −150.1 (tt, 1F, J_para,meta = 21, J_para,ortho = 4, F-para), −160.9 (br.s, 2F, F-meta).

(1-Chloro-2,2,3,3,3-pentafluoropropyl)pentafluorobenzene (23b) in the mixture with compound 45 (23b:45 = 79:21). Colorless liquid. ¹H NMR (CDCl₃): δ 5.58 (ddt, 1H, J_H,F(B) = 13.5, J_H,F(A) = 12.5, J_H,F(ortho) = 1.5, CHCl). ¹⁹F NMR (CDCl₃): δ −82.6 (s, 3F, CF₃), −118.5 (ddd, 1F, J_A,B = 267, J_A,ortho = 31.5, J_H,F(A) = 12.5, CF₂-F_A), −119.4 (ddd, 1F, J_A,B = 267, J_B,ortho = 28.5, J_H,F(B) = 13.5, CF₂-F_B), −133.6 (br.s, 1F, F-ortho), −141.9 (br.s, 1F, F-ortho), −149.7 (tt, 1F, J_para,meta = 21, J_para,ortho = 4, F-para), −160.3 (br.s, 1F, F-meta), −161.3 (br.s, 1F, F-meta). HRMS, m/z: calcd. for C₉H₁Cl₁F₁₀ 333.9602; found 333.9607.

1-(1-Chloro-2,2,3,3,3-pentafluoropropyl)-4-chloro-2,3,5,6-tetrafluorobenzene (45) in the mixture with compound 23b (23b:45 = 79:21). ¹H NMR (CDCl₃): δ 5.60 (ddt, 1H, J_H,F(B) = 13.5, J_H,F(A) = 12.5, J_H,F(2) = J_H,F(6) = 1.5, CHCl). ¹⁹F NMR (CDCl₃): δ −82.6 (s, 3F, CF₃), −118.4 (ddd, 1F, J_A,B = 267, J_A,ortho = 31.5, J_H,F(A) = 12.5, CF₂-F_A), −119.3 (ddd, 1F, J_A,B = 267, J_B,ortho = 28.5, J_H,F(B) = 13.5, CF₂-F_B), −133.6 (br.s, 1F, F-2,6), −139.3 (br.s, 1F, F-3,5), −140.3 (br.s, 1F, F-3,5), −141.7 (br.s, 1F, F-2,6). HRMS, m/z: calcd. for C₉H₁Cl₂F₉ 349.9306; found 349.9309.

1-Chloro-2,2,3,3,4,4,5,6,7,8-decafluorotetralin (23c) in the mixture with compound 47 (23c:47 = 92:8). Colorless liquid. ¹H NMR (CDCl₃): δ 5.52 (dt, 1H, J = 10.5, J = 4, H-1). ¹⁹F NMR (CDCl₃): −97.9 (dm, 1F, J_A,B = 291, F_A-4), −114.5 (dm, 1F, J_A,B = 291, F_B-4), −115.4 (dm, 1F, J_A,B = 273, F_A-2), −123.7 (dm, 1F, J_A,B = 273, F_A-3), −125.4 (dm, 1F, J_A,B = 273, F_B-2), −136.2 (dddd, 1F, F-8), −136.6 (ddddd, 1F, F-5), −143.1 (dm, 1F, J_A,B = 273, F_B-3), −146.2 (dddd, 1F, F-7), −148.6 (ddd, 1F, F-6); J_5,A4 = 8.5, J_5,B4 = 29.5, J_5,6 = 20.5, J_5,7 = 8, J_5,8 = 12, J_6,7 = 20.5, J_6,8 = 7, J_7,8 = 20.5, J_7,A4 = 3, J_8,B4 = 2.5. HRMS, m/z: calcd. for C₁₀H₁Cl₁₀F₉ 345.9602; found 345.9600.

7-Chloro-1,1,2,2,3,3,5,6,7,8-decafluoro-1,2,3,7-tetrahydronaphthalene (47) in the mixture with compound 23c (23c:47 = 92:8). ¹H NMR (CDCl₃): δ 6.54 (m, 1H, H-1). ¹⁹F NMR (CDCl₃): −107.5 (ddm, 1F, J_7,8 = 28.5, J_6,7 = 26.5, F-7), −110.2 (br.d, 1F, J_A,B ~ 300, F_A-1 or 3), −111.8 (br.d, 1F, J_A,B ~ 300, F_B-1 or 3), −111.8 (td, 1F, J_1,8 = 29, J_7,8 = 28.5, F-8), −114.4 (br.d, 1F, J_A,B ~ 290, F_A-1 or 3), −116.8 (br.d, 1F, J_A,B ~ 290, F_B-1 or 3), −137.7 (br.d, 1F, J_A,B ~ 270, F_A-2), −139.9 (br.d, 1F, J_A,B ~ 270, F_B-2), −145.4 (dm, 1F, J_6,7 = 26.5, F-6), −150.1 (m, 1F, F-5).

1,4-Dichloro-2,2,3,3,5,6,7,8-octafluorotetralin (36) (isomers A:B = 64:36). Colorless liquid. Isomer A. ¹H NMR (CDCl₃): δ 5.53 (m, 2H, H-1,4). ¹⁹F NMR (CDCl₃): −109.6 (dm, 2F, J ~ 280, CF₂), −125.8 (dm, 2F, J ~ 280, CF₂), −137.3 (m, 2F, F-5,8), −150.6 (m, 2F, F-6,7). Isomer B. ¹H NMR (CDCl₃): δ 5.45 (m, 2H, H-1,4). ¹⁹F NMR (CDCl₃): −118.0 (dm, 2F, J ~ 260, CF₂), −119.1 (dm, 2F, J ~ 260, CF₂), −135.3 (m, 2F, F-5,8), −150.7 (m, 2F, F-6,7). HRMS, m/z: calcd. for C₁₀H₁Cl₂F₈ 343.9400; found 343.9403.

3.4.5. Synthesis of Fluoroderivatives 7a,d, and 18

a. A mixture of compound 8a (4.35 g, 20.1 mmol) and CsF (9.00 g, 59.2 mmol) was sealed in a glass tube and heated (10 h, 250–260 °C). Distillation of volatile product gave 3.44 g of compound 7a (yield 86%).

b. A mixture of compound 8d (0.740 g, 2.78 mmol) and CsF (2.220 g, 14.6 mmol) was sealed in a glass tube and heated (9 h, 250–260 °C). Distillation of volatile product gave 0.560 g of compound 7d (yield 81%).

c. A mixture of compound 19 (2.75 g, 7.2 mmol) and CsF (6.39 g, 42.0 mmol) was sealed in a glass tube and heated (17 h, 250–260 °C). Steam distillation gave 1.706 g of compound 18 (yield 65%).

3.4.6. Synthesis of (1,2,2,3,3,3-Hexafluoropropyl)pentafluorobenzene (22b)

Alcohol 41b (3.664 g, 11.59 mmol) was added to a mixture of C₆F₅CF₃ (3.275 g, 13.88 mmol) with SbF₅ (2.516 g, 11.62 mmol), the resulting mixture was intensively stirred (4 h, 70 °C), poured into of 5% hydrochloric acid (25 mL), extracted with CH₂Cl₂ (2 × 10 mL), and dried over MgSO₄. The extract contained compounds 22b and pentafluorobenzoate of the starting alcohol (GC-MS, M = 510) in a 90:10 molar ratio, along with C₆F₅CF₃ and C₆F₅CO₂H. It was washed with a saturated aqueous solution of NaHCO₃ (60 mL), the solvent was evaporated, and fractional distillation of the residue in a vacuum (100 Torr) gave a fraction (1.828 g, bp 90 °C) containing 98% of compound 22b (yield 50%).

(1,2,2,3,3,3-Hexafluoropropyl)pentafluorobenzene (22b). Colorless liquid. ¹H NMR (CDCl₃): δ 6.11 (ddd, 1H, J_H,F(1) = 43, J_H,F(B) = 19, J_H,F(A) = 4, CHF). ¹⁹F NMR (CDCl₃): δ −83.6 (d, 3F, CF₃), −124.4 (ddtd, 1F, CF₂-F_A), −131.1 (ddtd, 1F, CF₂-F_B), −139.8 (m, 2F, F-ortho), −148.8 (ttd, 1F, F-para), −160.8 (br.s, 2F, F-meta), −206.0 (dddtqd, 1F, F-1); J_F(1),H = 43, J_1,A = 14.5, J_1,B = 15.5, J_1,3 = 10, J_1,ortho = 13, J_1,para = 2, J_A,B = 282.5, J_F(A),H = 4, J_A,ortho = 6.5, J_F(B),H = 19, J_B,ortho = 17, J_H,F(A) = 12.5, J_A,B = 267, J_H,F(B) = 13.5, J_para,meta = 21, J_para,ortho = 4. HRMS, m/z: calcd. for C₉H₁F₁₁ 317.9897; found 317.9893.

3.4.7. Synthesis of Acids 11–13

a. A mixture of acid 9e (0.524 g, 1.90 mmol), CF₃CO₂H (0.330 g, 2.89 mmol), and SbF₅ (1.690 g, 7.81 mmol) (molar ratio 1:1.5:4.1) was stirred at room temperature for 4.5 h, r.t., poured into 5% hydrochloric acid (20 mL), and extracted with Et₂O. The resulting solution contained compounds 9e and 11 in an 18:82 molar ratio. After evaporation of Et₂O, the residue was dissolved in a saturated aqueous solution of NaHCO₃ (50 mL), acidified with HCl (pH < 1), and extracted with CH₂Cl₂ (2 × 5 mL) to separate the acid 9e. The aqueous layer was extracted with Et₂O (3 × 5 mL). Evaporation of the solvent, sublimation (190 °C, 1 Torr), and recrystallization from CCl₄-acetone resulted in 0.337 g of acid 11 (yield 70%).

b. Acid 9d (0.559 g, 2.02 mmol), CF₃CO₂H (0.391 g, 3.42 mmol), and SbF₅ (1.956 g, 9.03 mmol) (molar ratio 1:1.7:4.5), similarly to previous procedure, gave a mixture of compounds 9d and 12 in a 15:85 molar ratio. Evaporation of the solvent fractional sublimation (130 °C, 1 Torr), then (210 °C, 1 Torr) and recrystallization of the second fraction from CCl₄-acetone gave 0.322 g of acid 12 (yield 63%).

c. In a manner analogous to [79], 4-methylheptafluorotoluene (0.565 g, 2.44 mmol) was dissolved in SbF₅ (3.175 g, 14.67 mmol), the resulting solution was poured into of 5% hydrochloric acid (30 mL), extracted with CH₂Cl₂ (2 × 10 mL), and dried over MgSO₄. The extract contained compound 13 and the starting compound in a 75:25 molar ratio. Evaporation of the solvent and sublimation (130 °C, 2 Torr) resulted in 0.312 g of acid 13 (yield 61%).

3-Carboxymethyl-2,4,5,6-tetrafluorobenzoic acid (11). White solid; mp 176.5–178 °C (CCl₄-acetone). IR (KBr) ν, cm⁻¹: 1705, 1743 (C=O), 1502, 1490, 1431, 1416 (FAR). ¹H NMR (acetone-d₆): δ 5.9 (br.s, 2H, COOH), 3.81 (s, 2H, CH₂). ¹⁹F NMR (acetone-d₆): δ −117.3 (dddt, 1F, F-2), −131.4 (dddt, 1F, F-4), −134.5 (dd, 1F, F-6), −164.9 (td, 1F, F-5); J_2,4 = 4, J_2,5 = 11, J_2,6 = 1.5, J_4,5 = 21, J_4,6 = 8, J_5,6 = 21, J_CH2,F(2) = J_CF2,F(4) = 1.5. HRMS, m/z: calcd. for C₉H₄O₄F₄ 252.0040; found 252.0038. Anal. calcd. for C₉H₄O₄F₄: C, 42.88; H, 1.60; F, 30.14%. Found: C, 43.3; H, 2.10; F, 30.26%.

4-Carboxymethyl-2,3,5,6-tetrafluorobenzoic acid (12). White solid; mp 216.5–218 °C (after sublimation). IR (KBr) ν, cm⁻¹: 1714 (C=O), 1495 (FAR). ¹H NMR (acetone-d₆): δ 5.9 (br.s, 2H, COOH), 3.91 (s, 2H, CH₂). ¹⁹F NMR (acetone-d₆): δ −141.2 (m, 2F), −141.9 (m, 2F). HRMS, m/z: calcd. for C₉H₄O₄F₄ 252.0040; found 252.0043. Anal. calcd. for C₉H₄O₄F₄: C, 42.88; H, 1.60; F, 30.14%. Found: C, 42.76; H, 1.35; F, 30.06%.

2,3,5,6-Tetrafluoro-4-methylbenzoic acid (13). White solid; mp 166–168 °C (after sublimation). IR (KBr) ν, cm⁻¹: 1730 (C=O), 1535, 1508, 1500, 1481 (FAR). ¹H NMR (acetone-d₆): δ 4.7 (br.s, 1H, COOH), 2.33 (t, 3H, CH₃, J_CH3,F(3) = J_CF3,F(5) = 2). ¹⁹F NMR (acetone-d₆): δ −141.6 (m, 2F, F-2,6), −142.7 (m, 2F, F-3,5).

4. Conclusions

The carbonylation at the benzyl C-Hal (Hal = F, Cl) bond of polyfluorinated alkyl aromatic compounds with different types of their aliphatic moiety in the CO–SbF₅ system, resulting in corresponding carboxylic acids, or their methyl esters was demonstrated. Polyfluorinated alkylaromatic compounds Ar_FCHHalR (R = Hal, H, Alk_F, C₆F₅) containing a hydrogen atom at the benzyl position undergo carbonylation in the CO–SbF₅ system; for CCl₂H derivatives, the possibility of selective mono- and dicarbonylation depending on the amount of SbF₅ was demonstrated, whereas for CF₂H derivatives, only dicarbonylation is possible. The carbonylation of para-substituted benzyl halides XC₆F₄CH₂Hal (X = Alk_F, C₆F₅, CH₂Cl), in contrast to meta- and ortho-isomers (X = CF₃, CH₂Cl), gives corresponding acids in low yields, due to side transformations of the starting compounds in an SbF₅ medium. The addition of CO to compounds Ar_FCHHalAlk_F can be accompanied by the elimination of HF, thus leading to saturated or α,β-unsaturated α-arylcarboxylic acids (or esters), with the outcome depending on the reaction conditions.