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Article

C-N, C-O and C-S Ullmann-Type Coupling Reactions of Arenediazonium o-Benzenedisulfonimides

by
Achille Antenucci
and
Stefano Dughera
*
Dipartimento di Chimica, Università di Torino, Via Pietro Giuria 7, 10125 Torino, Italy
*
Author to whom correspondence should be addressed.
Reactions 2022, 3(2), 300-311; https://doi.org/10.3390/reactions3020022
Submission received: 9 May 2022 / Revised: 24 May 2022 / Accepted: 29 May 2022 / Published: 2 June 2022
(This article belongs to the Special Issue Traditional and Innovative Catalysts for Reactions of Industrial Interest)
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Versions Notes

Abstract

:
Arenediazonium o-benzenedisulfonimides have been used as efficient electrophilic partners in Cu(I) catalysed Ullmann-type coupling. The synthetic protocols are mild and easy, and produced either N-alkylanilines, aryl ethers, or thioethers in fairly good yields (18 positive examples, average yield 66%). o-Benzenedisulfonimide was recovered at the end of the reactions and was reused to prepare the starting salts for further reactions. It is noteworthy that diazonium salts have been used as electrophilic partners in the Ullmann-type protocol for the first time.

1. Introduction

In recent years, the considerable efforts made in understanding the mechanism of Ullmann reaction [1,2], together with the urgency of cross-coupling protocols based on generally less costly and toxic first row transition metals [3] (e.g., iron [4], nickel [5], and copper [6,7]) rather than palladium, has led to a resurgence of this reaction. Indeed, although the classical Ullmann reaction is perhaps the most ancient cross coupling protocol [8,9], harsh reaction conditions (generally > 200 °C) and low yields drastically limited its applications, and consequently, its industrial employment.
Apart from being a powerful tool for the formation of a C(sp2)-C(sp2) bond between two aromatic rings (Ullmann homocoupling of aryl halides), even under mild reaction conditions [10,11], in optimal yields and excellent functional group tolerance [12,13,14,15,16], the Ullmann protocol also proved its usefulness and versatility in broader applications, including Cu-catalyzed nucleophilic aromatic substitution between various nucleophiles with aryl halides, known as Ullmann-type (or hetero-Ullmann) coupling (Scheme 1) [17,18,19,20,21,22,23,24,25,26,27,28]. These reactions can lead to moieties that are building blocks of active molecules in the life sciences [29] and in different material precursors [30]. Recent studies suggested that the copper catalyst may play a significant role in the activation of the aryl halide with evidence for an oxidative addition/reductive elimination process through a copper (III) intermediate (Scheme 1); however, in spite of this progress, the role of the ligand in the catalytic cycle remains relatively unresolved [12].
Aryl halides are generally the preferred electrophilic partners for Ullmann couplings; other types of compounds have only rarely been used. In particular, arenediazonium salts, which, in other coupling reactions, turn out to be a valid alternative to aryl halides [31,32], have been employed only sporadically in classical Ullmann homocoupling [33].
The industrial use of diazonium compounds has historically been limited from their intrinsic hazard [34] and instability, which depends, to a large extent on the reaction medium [35,36], the nature of the substrate (i.e., alkyl diazonium salts cannot be isolated), and of the counteranion [37], which has prompted the investigation of their decomposition kinetics [38]. As a result, the knowledge acquired on the chemistry of diazonium salts has even allowed for their application within the framework of particular reaction set-ups, such as flow reactors [39]. Once these issues have been pointed out, arenediazonium salts offer a series of advantages with respect to aryl halides. First of all, they possess better reactivity, due to the fact that the diazonium group is a better nucleofuge than the halide, which allows the use of mild reaction conditions. Second, as the nucleofuge is a gaseous species, it can work around the issue of high COD/BOD in wastewater, due to the presence of halide anions. Finally, reactions often do not require a base or additional ligands. Furthermore, our previous research has resulted in a large family of dry diazonium salts, namely, arenediazonium o-benzenedisulfonimides (Figure 1) [40,41,42,43,44,45,46,47,48,49,50,51]. The properties of these compounds indicate that they have great potential in numerous synthetic applications, as they are easy to prepare and isolate, they are extremely stable (in some cases more than the corresponding tetrafluoroborates), and they can be stored for an unlimited time. Moreover, they react smoothly both in water and organic solvents.
In light of this, in this study, we propose a mild, easy, and efficient revisitation of Ullmann-type couplings carried out by reacting suitable arenediazonium o-benzenedisulfonimides 1 with primary aliphatic amines 2a–c, in the presence of tetrakis(acetonitrile)copper hexafluorophosphate and 1,10-phenanthroline as a ligand (Scheme 2). It must be stressed that, to the best of our knowledge, diazonium salts have been used here as electrophilic partners in an Ullmman-type protocol for the first time.
The reaction, in the same conditions, was also extended to primary alcoholates 5a,b and thiolate 6a (Scheme 3).

2. Materials and Methods

2.1. General Informations

All the reactions were carried out in open air. Analytical grade reagents and solvents were used and reactions were monitored by GC, GC-MS, and TLC. Column chromatography and TLC were performed on Merck silica gel 60 (70–230 mesh ASTM) and GF 254, respectively. Petroleum ether refers to the fraction boiling in the range 40–70 °C. Room temperature is 22 °C. Mass spectra were recorded on an HP 5989B mass selective detector connected to an HP 5890 GC with a methyl silicone capillary column. 1H NMR and 13C NMR spectra were recorded on a Jeol ECZR spectrometer at 600 and 150 MHz, respectively. IR spectra were recorded on an IR PerkinElmer UATR-two spectrometer. Tetrakis(acetonitrile)copper hexafluorophosphate was prepared as reported in the literature [52]. Dry arenediazonium o-benzenedisulfonimides 1 were prepared as described previously by us [40]. The crude salts 1 were virtually pure (by 1H NMR spectroscopy) and were used in subsequent reactions without further crystallization. All the other reagents were purchased from Sigma-Aldrich or Alfa-Aesar. Structures and purity of all the products obtained in this research were confirmed by their spectral (NMR, MS) and physical data, which are substantially identical to those reported in the literature. Yields of the pure (GC, above 96%; GC-MS; TLC and NMR) isolated compounds 3, 7, 8 are collected in Table 1 and Table 2. NMR spectra of 3, 7, 8 are reported in the Supplementary Materials.

2.2. N-(n-Hexyl)-4-Nitroaniline (3a): Representative procedure for the Ullmann-Type Coupling Reactions of Arenediazonium o-Benzenedisulfonimides

Moreover, 4-Nitrobenzenediazonium o-benzenedisulfonimide (1a, 0.74 g, 2 mmol) was added to hexan-1-amine (2a, 0.22 g, 2.2 mmol), tetrakis(acetonitrile)copper hexafluorophosphate [(Me3CN)4Cu]PF6 (0.75 g, 2 mmol) and 1,10-phenanthroline (0.36 g, 2 mmol) in DMSO (5 mL). The resulting mixture was stirred at room temperature for 3 h; the completion of the reaction was confirmed by the absence of azo coupling with 2-naphthol. Then, the reaction mixture was poured into diethyl ether/water (100 mL, 1:1). The aqueous layer was separated and extracted with diethyl ether (50 mL). The combined organic extracts were washed with water (50 mL), dried with Na2SO4, and evaporated under reduced pressure. GC-MS analyses of the crude residue showed N-(n-hexyl)-4-nitroaniline (3a), MS (EI): m/z 222 (M+) as the major product, as well as traces of 4,4’-dinitrobiphenyl, MS (EI): m/z 244 (M+), 3-hexyl-1-(4-nitrophenyl)triaz-1-ene (4a), MS (EI): m/z 250 and nitrobenzene MS (EI): m/z 123 (M+). The crude residue was purified on a short column, eluting with petroleum ether/diethyl ether (9:1). The title compound 3a was obtained in 87% yield (0.39 g).
The aqueous layer and aqueous washings were collected and evaporated under reduced pressure. The tarry residue was passed through a column of Dowex HCR-W2 ion exchange resin (1.6 g/1 g of product), eluting with water (about 50 mL). After removal of water under reduced pressure, virtually pure (1H NMR) o-benzenedisulfonimide was recovered (0.360 g, 81% yield; mp 192–194 °C. Lit. 190–193 °C).

3. Results and Discussion

A model reaction between 4-nitrobenzenediazonium o-benzenedisulfonimmide (1a) and hexan-1-amine (2a) were studied under various conditions (Table 1), in order to optimize the reaction conditions. First of all, the reaction carried out in absence of copper, with THF as a solvent, only provided the corresponding triazene 4, as it is logical to expect, on the basis of the well-known reactivity of the diazonium salts with aliphatic amines (Table 1; entry 1) [53,54].
Table
Table 1. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and amines 2.
Table 1. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and amines 2.
Reactions 03 00022 i001
EntrySalt 1Amines 2Cu and Ligand (L)SolventT
(°C)		Time (h)Products 3 and
Yields (%) 1		Literature
Yields (%)
1 Reactions 03 00022 i002
1a		n-C6H13NH2
2a		-THFrt3- 2
21a2aCuTHFrt3- 3
31a2aCuClTHFrt3- 4
41a2aCuITHFrt2- 5
51a2aCu2OTHFrt3- 6
61a2a[(MeCN)4Cu]PF6THFrt2 Reactions 03 00022 i003
3a; 27 7
71a2a[(MeCN)4Cu]PF6THF501- 8
81a2a[(MeCN)4Cu]PF6EtOHrt23a; 34 7
91a2a[(MeCN)4Cu]PF6MeCNrt33a; 30 7
101a2a[(MeCN)4Cu]PF6DMSOrt23a; 48 7
111a2a[(MeCN)4Cu]PF6/LDMSOrt23a; 87 7,987 [55]
12 Reactions 03 00022 i004
1b		2a[(MeCN)4Cu]PF6/LDMSOrt4 Reactions 03 00022 i005
3b; 79 10		94 [55]
131b Reactions 03 00022 i006
2b		[(MeCN)4Cu]PF6/LDMSOrt3 Reactions 03 00022 i007
3c; 73 10		95 [20]
141a2b[(MeCN)4Cu]PF6/LDMSOrt3.5 Reactions 03 00022 i008
3d; 85 10		91 [56]
15 Reactions 03 00022 i009
1c		2a[(MeCN)4Cu]PF6/LDMSOrt4 Reactions 03 00022 i010
3e; 51 10		85 [57]
16 Reactions 03 00022 i011
1d		2a[(MeCN)4Cu]PF6/LDMSOrt2 Reactions 03 00022 i012
3f; 86 10		78 [58]
17 Reactions 03 00022 i013
1e		2a[(MeCN)4Cu]PF6/LDMSOrt5 Reactions 03 00022 i014
3g; 46 10		56 [59]
18 Reactions 03 00022 i015
1f		2a[(MeCN)4Cu]PF6/LDMSOrt3 Reactions 03 00022 i016
3h; 51 10		98 [22]
19 Reactions 03 00022 i017
1g		2a[(MeCN)4Cu]PF6/LDMSOrt3 Reactions 03 00022 i018
3i; 86 10		87 [60]
201a Reactions 03 00022 i019
2c		[(MeCN)4Cu]PF6/LDMSOrt2 Reactions 03 00022 i020
3j; 79 10		78 [61]
211a Reactions 03 00022 i021
2d		[(MeCN)4Cu]PF6/L
DMSOrt2- 11
221a Reactions 03 00022 i022
2e		[(MeCN)4Cu]PF6/LDMSOrt3- 11
1 The reactions were carried out with 2 mmol of 1, 2.2 mmol of 2, 2 mmol of Cu(I) adduct, and 2 mmol of ligand. Yields refer to pure and chromatographic column isolated 3. 2 The main product was 3-hexyl-1-(4-nitrophenyl)triaz-1-ene (4a). 3 GC-MS analyses of crude residues showed the presence of 4a, 4,4′-dinitrobiphenyl and nitrobenzene. 4 GC-MS analyses of crude residues showed the presence of 4a, 4,4′-dinitrobiphenyl, nitrobenzene 1-chloro-4-nitrobenzene. 5 GC-MS analyses of crude residues showed the presence of 4a, 4,4′-dinitrobiphenyl, nitrobenzene and 1-iodo-4-nitrobenzene. 6 GC-MS analyses of crude residues showed the presence of 4a, 4,4′-dinitrobiphenyl, nitrobenzene and 3a. 7 GC-MS analyses of crude residues showed, as well as 3a as the main product, the presence of 4a, 4,4′-dinitrobiphenyl, and nitrobenzene. 8 Decomposition of 1a occurred. 9 Lower amounts of [(MeCN)4Cu]PF6 and 1,10-phenanthroline led to significantly lower yields. 10 GC-MS analyses of crude residues always showed the presence of triazenes 4, arenes and symmetrical biaryls as by-products. 11 The only product was corresponding triazene 4.
In order to favor the hetero-Ullmann coupling, a number of copper derivatives such as powdered Cu (Table 1; entry 2) or Cu (I) (copper chloride, copper iodide or cuprous oxide) were added (Table 1; entries 3−5) in stoichiometric amounts. The products were triazene 4a, together with variable amounts of 1-chloro or 1-iodo-4-nitrobenzene, nitrobenzene, 4,4’-dinitrobiphenyl. Traces of target 3a were formed only in the presence of cuprous oxide (Table 1; entry 6). At this point we decided to use another Cu (I) adduct, namely tetrakis(acetonitrile)copper hexafluorophosphate (easily prepared from Cu(II)SO4 and Cu powder, in the presence of KPF6 and NCMe [52]), which was unable to favor the classic Sandmeyer reaction [53,54]. GC-MS analyses showed the formation of the desired coupling adduct 3a. (Table 1; entry 6). Other solvents were then tested and the best results were obtained in DMSO (Table 1; entry 10). A suitable ligand (1,10-phenanthroline: Table 1; entry 11) was then added, in a stoichiometric amount; to our delight, the main product of the reaction was 3a, obtained with a good yield (87%), after carrying out the reaction at room temperature and in a relatively short time. It is interesting to note that the reactions were carried out without additional bases and that lower amounts of [(MeCN)4Cu]PF6 and 1,10-phenanthroline led to significantly lower yields (Table 1, entry 11: footnote 9).
The amine 2a was then reacted with other diazonium salts, 1a–f, which were variously substituted with electron donor groups or electron-withdrawing groups. The target compounds, 3b–j (Table 1; entries 12–20), were obtained in fair to good yields and selectivity while producing relatively low amounts of by-products, among which, the main one is always the triazene. The reaction was chemoselective; diazonium salt 1g, bearing a iodine atom that could potentially react as a diazonium group, only furnished target product 3i (Table 1; entry 19); no traces of possible diamine were detected. The reaction was also regioselective; in fact, where the amino group and the hydroxyl group are present in the same structure 2c, only the first reacted, with the formation of compound 3j. (Table 1; entry 20) Good results were also achieved with another primary amine, such as benzylamine (2b: Table 1; entries 13 and 14). Finally, we decided to change the type of amine and use a secondary amine, namely, diethylamine (2d). The reaction failed; the only obtained product, even in the presence of catalyst and ligands, was triazene (Table 1; entry 21). The same results were obtained using aniline (2e: Table 1; entry 22).
In order to expand the scope of our research, we also decided to study C-O and C-S Ullmann coupling.
It is well known that arenediazonium salts undergo the O-coupling reaction with alcohols, mainly under acidic conditions [53,54]. The products of this coupling, namely, diazo ethers, (Ar-N=N-O-R), initiate a radical mechanism, which, through the formation of aryl radicals, yield reduction products (arenes).
However, some synthetic protocols, allow aryl alkyl ethers to be obtained via the reaction (usually at high temperature) of diazonium salts with various alcohols, are reported in the literature [62,63].
On this basis, a model reaction between 4-nitrobenzenediazonium (1a) and hexan-1-ol was studied (Table 2). Unfortunately, the hexan-1-ol did not react under the optimum conditions set up above (Table 2; entries 2 and 3).
Table
Table 2. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and alcoholates 5 and thiolate 6.
Table 2. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and alcoholates 5 and thiolate 6.
Reactions 03 00022 i023
EntrySalt 1Alcolholates 5 or
Thiolate 6		Cu(I) and Ligand (L)SolventT
(°C)		Time
(h)		Products 7 and 8
and Yields (%) 1		Literature
Yields (%)
1 Reactions 03 00022 i024
1a		n-C6H13OH-DMSOrt24- 2
21an-C6H13OH[(MeCN)4Cu]PF6/LDMSOrt24- 3
31an-C6H13OH[(MeCN)4Cu]PF6/LDMSO503- 4
41a Reactions 03 00022 i025
5a		[(MeCN)4Cu]PF6DMSOrt24 Reactions 03 00022 i026
7a; 34 3
51a5a[(MeCN)4Cu]PF6/LDMSOrt37a; 67 5,6
6 Reactions 03 00022 i027
1b		5a[(MeCN)4Cu]PF6/LDMSOrt6 Reactions 03 00022 i028
7b; 49 7		78 [19]
7 Reactions 03 00022 i029
1h		 Reactions 03 00022 i030
5b		[(MeCN)4Cu]PF6/LDMSOrt4 Reactions 03 00022 i031
7c; 64 7
81h5b[(MeCN)4Cu]PF6/LEtOHrt27c; 67 774 [64]
9 Reactions 03 00022 i032
1i		5b[(MeCN)4Cu]PF6/LEtOHrt4 Reactions 03 00022 i033
7d; 66 7		100 [65]
10 Reactions 03 00022 i034
1j		5b[(MeCN)4Cu]PF6/LEtOHrt4 Reactions 03 00022 i035
7e; 51 7
11 Reactions 03 00022 i036
1k		5b[(MeCN)4Cu]PF6/LEtOHrt3 Reactions 03 00022 i037
7f; 60 7
121a Reactions 03 00022 i038
5c		[(MeCN)4Cu]PF6/LDMSOrt24- 8
131a5c[(MeCN)4Cu]PF6/LDMSO504- 8
141a5c[(MeCN)4Cu]PF6/LiPrOHrt24- 8
151an-C4H9SH-DMSOrt24- 2
161an-C4H9SH[(MeCN)4Cu]PF6/LDMSO508- 3
171a Reactions 03 00022 i039
6a		[(MeCN)4Cu]PF6/LDMSOrt2 Reactions 03 00022 i040
8a; 65 7
181b6a[(MeCN)4Cu]PF6/LDMSOrt6 Reactions 03 00022 i041
8b; 48 7		65 [66]
1 The reactions were carried out with 2 mmol of 1, 2.2 mmol of 5 and 6, 2 mmol of Cu(I) adduct, and 2 mmol of ligand. Yields refer to pure and chromatographic column isolated, 7,8. 2 After 24 h, 1a had not reacted. GC-MS analyses of a sample showed the presence of nitrobenzene. 3 After 24 h, 1a had still not reacted. GC-MS analyses of a sample showed the presence of nitrobenzene and 7a. 4 Decomposition of 1a occurred. 5 GC-MS analyses of crude residues also showed the presence of nitrobenzene and 4,4′-dinitrobiphenyl. 6 Lower amounts of [(MeCN)4Cu]PF6 and 1,10-phenanthroline, which led to significantly lower yields.7 GC-MS analyses of crude residues always showed the presence of arenes and symmetrical biaryls as by-products. 8 Only traces of isopropyl phenyl ether were detected. The main product was nitrobenzene.
Moreover, we decided to previously treat the hexanol with sodium hydride to transform it into the corresponding alcoholate, 5a. To our surprise, we obtained the target product, 7a, with a good yield (Table 2; entry 4). It must be stressed that the reaction that was carried out with a secondary alkoxide (Table 2; entries 12 and 13) did not lead to significant results. In this case, the only product was nitrobenzene.
Heteroarene tetrafluoroborate is rather unstable and sometimes are difficult to isolate [34]; in the light of this, we synthesized three, more stable and easy to handle, heteroarene diazonium o-benzenedisulfonimides, 1i–k, and, as reported in Table 2, the reactions carried out in the presence of these salts and sodium ethoxide (5b) in ethanol provided ethers 7d–f in fairly good yields (Table 2; entries 9–11).
Finally, under the same conditions as the primary alcoholates, primary thiolate 6a was prepared and gave good yields of the C-S coupling product, aryl alkyl sulfide 8a,b (Table 2; entries 17 and 18).
In conclusion, the target products, 3, 7, 8, were obtained in discrete yields, but sometimes, the yields were lower than those reported in the literature for the same products obtained with different Ullmann-type reactions, using aryl halides as electrophiles (Table 1 and Table 2); however, it is necessary to highlight that generally, these latter reactions are carried out at high temperatures under strictly controlled conditions (e.g., in an inert atmosphere and/or in a sealed vial) with long reaction times. On the contrary, by using diazonium salts as an alternative to aryl halides, the reactions can be carried out in milder conditions (for example, at room temperature, in open air vials and with shorter reaction times)
It is worth noting that it was possible to recover o-benzenedisulfonimide at a yield of more than 80% from all the reactions described above. It was also possible to recycle it for the preparation of other salts 1, with economic and ecological benefits.
In order to formulate a convincing hypothesis on the mechanism of this Ullmann-type coupling, two reactions, reported in Table 1 (entry 11) and Table 2 (entry 5), were carried out in the presence of TEMPO, a well-known radical scavenger; a sharp decrease in the yields of 3a and 7a were observed. In light of this, and inspired by Kochi’s previous mechanistic studies [1,67], we hypothesized a radical SRN1-type mechanism, as shown in Scheme 4. It must be stressed that dediazoniations initiated by an electron transfer are well-known reactions of diazonium salts [7,35,53].
We believe that in step 1, there may be competition between the Cu (I) adduct and the nucleophile (ammine, alcoholate or thiolate). This could explain why a stoichiometric amount of Cu (I) adduct is needed, so that the coupling products 3, 7, 8 can be formed. On the other hand, the ligand 1,10-phenanthroline, stabilizing the Cu (I) adduct, would facilitate its interaction with the diazonium salt, and consequently step 3. Indeed, copper catalysis is not necessary to produce aryl alkyl sulfides 8; they can be easily obtained with the classic Stadler–Ziegler reaction [68]; however, this reaction is dangerous to carry out as a result of the intermediate formation and accumulation of the highly explosive diazosulfides. In our previous paper [68], we developed an efficient and safe modification of the Stadler–Ziegler reaction, in which the formation of disulfides always occurred as by-products. Carrying out the reaction in the presence of Cu(I) as a catalyst, we never observed the formation of disulfides. This leads us to believe that the reaction mechanism, shown in Scheme 4, may also be plausible with thiolates 6.

4. Conclusions

We have proposed a mild, easy and efficient Ullmann-type coupling of arenediazonium and heteroarenediazonium o-benzenedisulfonimides. The target products were generally obtained in fairly good yields (18 positive examples, 66% average yield). To the best of our knowledge, in this study, diazonium salts have been used as electrophilic partners in an Ullmman-type protocol for the first time.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/reactions3020022/s1, Physical and NMR data of anilines 3, NMR spectra of anilines 3, Physical and NMR data of ethers 6, NMR spectra of ethers 6, Physical and NMR data of thioethers 7, NMR spectra of thioethers 7. Figures S1–S18, such as Figure S1: NMR spectra of N-(n-Hexyl)-4-Nitroaniline (3a). Figure S2: NMR spectra of N-(n-Hexyl)-4-Methoxyaniline (3b). Figure S3: NMR spectra of N-(n-Benzyl)-4-Methoxyaniline (3c). Figure S4: NMR spectra of N-(n-Benzyl)-4-Nitroaniline (3d). Figure S5: NMR spectra of N-(n-Hexyl)-2-Nitroaniline (3e). Figure S6: NMR spectra of N-(n-Hexyl)-3-Nitroaniline (3f). Figure S7: NMR spectra of N-(n-Hexyl)-2-Toluidine (3g). Figure S8: NMR spectra of N-(n-Hexyl)-3-Toluidine (3h). Figure S9: NMR spectra of NMR spectra of N-(n-Hexyl)-4-Iodoaniline (3i). Figure S10: NMR spectra of 2-[(4-Nitrophenyl)amino]Ethan-1-ol (3j). Figure S11: NMR spectra of 1-(n-Hexyloxy)-4-Nitrobenzene (7a). Figure S12: NMR spectra of 1-(n-Hexyloxy)-4-Methoxybenzene (7b). Figure S13: NMR spectra of 2-Ethoxynaphthalene (7c). Figure S14: NMR spectra of 2-Ethoxybenzo[d]thiazole (7d). Figure S15: NMR spectra of Methyl 3-Ethoxythiophene-2-carboxylate (7e). Figure S16: NMR spectra of 3-Ethoxypyridine (7f). Figure S17: n-Butyl 4-Nitrophenyl Sulfide (8a). Figure S18: n-Butyl 4-Tolyl Sulfide (8b). References[69,70,71,72] are cited in the supplementary materials.

Author Contributions

Conceptualization, S.D. and A.A.; methodology, S.D.; software, S.D.; validation, S.D. and A.A.; formal analysis, S.D.; investigation, S.D. and A.A.; resources, S.D.; data curation, S.D. and A.A.; writing—original draft preparation, S.D. and A.A.; writing—review and editing, S.D. and A.A.; visualization, S.D. and A.A.; supervision, S.D.; project administration, S.D.; funding acquisition, S.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data reported in this article can be obtained from the authors upon reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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Reactions 03 00022 sch001 550
Scheme 1. Ullmann homocoupling and Ullmann-type coupling.
Scheme 1. Ullmann homocoupling and Ullmann-type coupling.
Reactions 03 00022 sch001
Reactions 03 00022 g001 550
Figure 1. Arenediazonium o-benzenedisulfonimides 1.
Figure 1. Arenediazonium o-benzenedisulfonimides 1.
Reactions 03 00022 g001
Reactions 03 00022 sch002 550
Scheme 2. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and amines 2.
Scheme 2. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and amines 2.
Reactions 03 00022 sch002
Reactions 03 00022 sch003 550
Scheme 3. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and primary alcoholates 5a,b and thiolate 6a.
Scheme 3. Ullmann-type coupling between arenediazonium o-benzenedisulfonimides 1 and primary alcoholates 5a,b and thiolate 6a.
Reactions 03 00022 sch003
Reactions 03 00022 sch004 550
Scheme 4. Ullmann-type coupling: hypothesis of mechanism.
Scheme 4. Ullmann-type coupling: hypothesis of mechanism.
Reactions 03 00022 sch004
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Antenucci, A.; Dughera, S. C-N, C-O and C-S Ullmann-Type Coupling Reactions of Arenediazonium o-Benzenedisulfonimides. Reactions 2022, 3, 300-311. https://doi.org/10.3390/reactions3020022

AMA Style

Antenucci A, Dughera S. C-N, C-O and C-S Ullmann-Type Coupling Reactions of Arenediazonium o-Benzenedisulfonimides. Reactions. 2022; 3(2):300-311. https://doi.org/10.3390/reactions3020022

Chicago/Turabian Style

Antenucci, Achille, and Stefano Dughera. 2022. "C-N, C-O and C-S Ullmann-Type Coupling Reactions of Arenediazonium o-Benzenedisulfonimides" Reactions 3, no. 2: 300-311. https://doi.org/10.3390/reactions3020022

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