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Article

Heterocyclic Analogs of Thioflavones: Synthesis and NMR Spectroscopic Investigations

by
Ferdinand C. Fuchs
,
Gernot A. Eller
and
Wolfgang Holzer
*
Department of Drug and Natural Product Synthesis, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
*
Author to whom correspondence should be addressed.
†
Dedicated to Prof. Peter Stanetty with best personal wishes on the occasion of his 65th birthday.
Molecules 2009, 14(9), 3814-3832; https://doi.org/10.3390/molecules14093814
Submission received: 3 September 2009 / Revised: 11 September 2009 / Accepted: 21 September 2009 / Published: 25 September 2009
(This article belongs to the Special Issue Advances in Heterocyclic Chemistry)
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Versions Notes

Abstract

:
The synthesis of several hitherto unknown heterocyclic ring systems derived from thioflavone is described. Coupling of various o-haloheteroarenecarbonyl chlorides with phenylacetylene gives 1-(o-haloheteroaryl)-3-phenylprop-2-yn-1-ones, which were treated with NaSH in refluxing ethanol to yield the corresponding bi- and tricyclic annelated 2-phenylthiopyran-4-ones. Detailed NMR spectroscopic investigations of the ring systems and their precursors are presented.

Graphical Abstract

1. Introduction

The flavone system (2-phenyl-4H-chromen-4-one, shown in Figure 1, is the core of many biologically active compounds which play important roles in numerous biological processes. The relevance of flavone-based molecules has been thoroughly described in the literature [1,2,3,4,5]. Replacement of the ring oxygen atom in flavone by a sulfur atom results in thioflavone (4a, Figure 1), whose derivatives also exhibit interesting biological properties [6,7,8,9,10,11,12,13]. Moreover, thioflavones are valuable precursors for the synthesis of other condensed heterocyclic systems, such as benzothiazepines [14]. Analogs of type 4 thioflavone-systems – in which the condensed benzene ring of 4a is replaced by a heteroaromatic moiety (Figure 1) – seem to be of notable interest considering the concept of bioisosterism [15,16,17]. Type 4 compounds with a pyridine, thiophene, benzo[b]thiophene or indole system annelated to the thiopyrane ring have been previously characterized.
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Figure 1. Flavone, thioflavone and its heterocyclic analogs 4.
Figure 1. Flavone, thioflavone and its heterocyclic analogs 4.
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Various approaches have been used to synthesize type 4 systems. Representative examples are given in Scheme 1.
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Scheme 1. Traditional approaches to the title compounds 4.
Scheme 1. Traditional approaches to the title compounds 4.
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For instance, condensation of appropriate thiophenols A with ethyl benzoylacetate followed by subsequent cyclization of the obtained condensation products permits access to type 4 systems [18]. Another approach was employed by Becher in the synthesis of 2-phenyl-4H-thiopyrano[2,3-b]pyridin-4-one (4f) [19]. Ethyl 2-chloronicotinate (B) was transformed into the 2-tert-butyl congener C, which was condensed with acetophenone to yield D; the latter readily cyclized into 4f in an acidic medium. Moreover, the reaction between phenylpropiolates and thiophenols A and subsequent ring closure reaction of the formed substituted cinnamates E has also been used [20,21], for instance, in the synthesis of indole annelated 2-phenylthiopyran-4-ones [22]. Variants of 4 containing a thiophene or a benzo[b]thiophene moiety have been prepared via Friedel–Crafts acylation of the corresponding methylthio(benzo)thiophenes F with cinnamoyl chloride, to yield ketones G, and addition of bromine to the alkene double bond (compounds H) and subsequent cyclization with pyridine hydrochloride [23,24,25]. However, many of these methods require precursors that are neither commercially available nor readily synthesized. Moreover, the other above-mentioned approaches lack generality. For example, Friedel-Crafts-based methods are restricted to π-excessive heteroaromatic systems.
Here, we present a general approach for synthesizing heterocyclic analogs of type 4 based on a Sonogashira-type coupling of o-halo(hetero)aroyl chlorides 1 with phenylacetylene to yield alkynones 2 (Scheme 2). Reactions between 2 and NaSH in refluxing ethanol then yield the desired compounds 4 via an addition/cyclization step (Scheme 2). A related approach to thioflavone generation employing a microwave-assisted one-pot, three-component synthesis has been recently described by Müller [26] (based on an earlier report by Shvartsberg [27,28]). In the course of these investigations, the acetylenic component was varied to obtain different 2-substituted 4H-thiochromen-4-ones [26].
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Scheme 2. Preparation of compounds 4a-h.
Scheme 2. Preparation of compounds 4a-h.
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2. Results and Discussion

2.1. Chemistry

Synthesis of the target compounds 4 was accomplished via the sequence shown in Scheme 2. Precursors 1 are either commercially available or can be easily prepared by treatment of the corresponding carboxylic acids with thionyl chloride. Compounds 1 were transformed into 2 via Sonogashira-type coupling [29,30], a very important step in forming C-C bonds with terminal acetylenes [31]. A ligand- and copper-free Pd-catalyzed (Pd acetate, Et3N) version of this method for the coupling of carboxylic acid chlorides with different terminal acetylenes has been recently described by Nájera [32] and Srinivasan [33]. In preliminary tests in which the solvent, amount of triethylamine and the acid chloride/phenylacetylene ratio were varied, we adapted the reaction conditions for synthesis of the desired o-halo(hetero)arylynones 2a–h. The best results were obtained using two equivalents of acid chloride, a 3–14-fold molar excess of triethylamine, dichloromethane as the solvent and ambient temperature. Reasonably good yields of ynones 2a–h were obtained applying these reaction conditions. However, using of 1i and 1j as starting materials (both having the COCl group attached in the o-position to a pyridine-type nitrogen atom), we did not obtain the corresponding coupling products 2i or 2j. Instead, the respective N,N-diethylamides 5 and 6 were isolated as the main reaction products from the complex reaction mixtures (Scheme 3). A few reports in the literature have described N,N-diethylamide formation from acid chlorides and triethylamine [30,34,35].
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Scheme 3. Unexpected formation of N,N-diethylamides 5 and 6.
Scheme 3. Unexpected formation of N,N-diethylamides 5 and 6.
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NaSH in refluxing ethanol (96%) was used for the conversion of ynones 2a–h into thiopyranones 4a–h (Scheme 2). In principle, it is possible to use Na2S as the SH donor [27,28]; however, poor results were obtained using this technique. Evidence of the proposed mechanism, a Michael addition of the hydrosulfide to the alkynone system [26], was obtained in the following experiment. When 2a1 was reacted with NaSH/ethanol at room temperature, we isolated a sulfur-containing product that contained a chlorine atom and an enone group. The high-resolution mass spectrum and the spectral data demonstrated that the product was not the expected intermediate 3a1, but rather the thioether 7 (Scheme 4), formed following reaction between two units of 3a1 by elimination of hydrogen sulfide. The cis-position of alkene-H and the phenyl ring was confirmed by an NOE-difference experiment that employed irradiation of alkene-H resonance (Scheme 4).
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Scheme 4. Formation of thioether 7 from Michael addition intermediate 3a1.
Scheme 4. Formation of thioether 7 from Michael addition intermediate 3a1.
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Initial attempts to synthesize 4a and 4f in a one-pot/two-step procedure (reactants: 1a or 1f, respectively, with phenylacetylene, by Pd(OAc)2/triethylamine catalysis in solvent; then addition of Na2S in DMF) gave low yields (<16%) of the desired thiopyranones.
The ynones 2 described here are valuable precursors in the synthesis of other condensed heterocyclic systems, such as annelated pyridin-4-ones 8 and pyran-4-ones 9 (Scheme 5). For example, 2a1 was reacted with methylamine to generate the corresponding Michael addition product 10 at a 73% yield (stereochemistry demonstrated by a NOESY experiment). Treatment of product 10 with K2CO3 in dry DMF gave 1-methyl-2-phenyl-4(1H)-quinolinone (11) at a good yield. This type of compound was reported to exhibit interesting biological properties, such as anti-platelet [36], anti-mitotic [37], and anti-HIV-replication activity [38]. Furthermore, the well-known class of fluoroquinolinone type [39] antibacterial drugs, such as ciprofloxacin [40] or enoxacin [41], are structurally similar to 11. Investigations into the preparation of heterocyclic annelated pyridin-4-ones of type 8 are currently in progress and will be reported elsewhere.
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Scheme 5. Further synthetic potential of ynones 2.
Scheme 5. Further synthetic potential of ynones 2.
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2.2. Spectroscopic investigations

Alkynones 2 and thiopyranones 4 are predominantly novel structures. Representative structures (2a1, 2a2, 4a, 4d–f) have not been thoroughly investigated by spectroscopic methods, such as NMR. In regards to 13C-NMR spectroscopy – in cases where such data are available (4a, 4f) – little [19] to no [27,28] signal assignments have been made. Hence, we present the results from an extensive NMR study (1H, 13C, 15N) of compounds 2 and 4. Reliable and unambiguously assigned chemical shift data are important reference material for NMR prediction programs, such as CSEARCH [42]/NMRPRE-DICT [43] and ACD/C + H predictor [44]. Such programs have become very popular in the last few years, particularly for predicting 13C-NMR chemical shifts. However, the quality of such predictions is highly dependent on the availability of authentic reference data from related structures. This criterion is frequently unfulfilled for rare condensed heteroaromatic systems, such as those described here.
Full and unambiguous assignment of all 1H, 13C and 15N resonances was achieved by combining standard NMR techniques [45], such as fully 1H-coupled 13C-NMR spectra, APT, HMQC, gs-HSQC, gs-HMBC, COSY, TOCSY, NOESY and NOE-difference spectroscopy. Moreover, experiments with selective excitation (DANTE) of certain 1H-resonances were performed, such as long-range INEPT [46] and 2D(δ, J) long-range INEPT [47]. The latter experiments were indispensable for the unambiguous mapping of long-range 13C,1H coupling constants. Aside from the variable heteroaromatic system, the obtained data of the invariant parts of 2 and 4 show a high degree of consistency. Thus, the 3-phenyl-2-propyn-1-one substructure in 2a–h exhibits a carbonyl C-1 shift of 168.3–176.7 ppm, a C-2 shift of 87.2–88.5 ppm, and a C-3 shift of 91.9–96.2 ppm. Alkyne C-atoms, C-2 and C-3, can be easily distinguished by their coupling patterns: the C-2 signal appears as a singlet in the 1H-coupled 13C-NMR spectrum, whereas the C-3 signal is a triplet due to 3J coupling with phenyl protons H-2/6 (which is confirmed by a correlation signal from the involved nuclei in the HMBC spectrum). The signals from the phenyl-C atoms are Ph C-1: 119.3–120.1 ppm, Ph C-2/6: 133.1–133.3 ppm, Ph C-3/5: 128.6–128.8 ppm and Ph C-4: 130.9–131.6 ppm. The thiopyranone system in compounds 4a–h is characterized by a chemical shift of 176.2–182.0 ppm for the carbonyl C-atom (split by a ~ 1 Hz 2J coupling to the adjacent =C-H), 122.1–125.0 ppm for =C-H (1J 163.3–164.8 Hz) and 151.5–155.1 ppm for S-C-Ph (2J to =CH ~ 3 Hz). The =C-H proton gives rise to a characteristic singlet signal between 6.99 and 7.32 ppm. As observed with compounds 2, systems 4 also exhibit small differences in Ph-C shifts within the series a–h (Ph C-1: 136.1–136.7 ppm, Ph C-2/6: 126.9–127.2 ppm, Ph C-3/5: 129.2–129.4 ppm, Ph C-4: 130.7–131.3 ppm). The descriptions of NMR spectra in the Experimental section were assigned based on systematic nomenclature and, hence, the numbering of atoms within the thiopyrane moiety is inconsistent.
The excellent utility of 2D (δ,J) long-range INEPT spectra with selective excitation for the definite mapping of 13C,1H coupling constants is demonstrated by an example presented in Figure 2. In the 1H-coupled 13C-NMR spectrum of 4d, the signal of C-7a is split by a 7.1, 5.9 and 4.7 Hz coupling, whereas coupling occurs with H-2, H-3 and H-6. Unequivocal assignment of these coupling constants based on literature data for the thiophene system is unreliable. However, after selective excitation of the H-2 resonance, the C-7a signal appears as a doublet of 5.9 Hz, thus 3J(C7a,H2) = 5.9 Hz (Figure 2). Moreover, the couplings 2J(C3,H2) = 4.8 Hz and 3J(C3a,H2) = 11.2 Hz emerge (Figure 2) (4J(C7,H2) = 1.1 Hz also appears, but it is not displayed in Figure 2). Further experiments with selective excitation of H-3 and H-6 assigned 3J(C7a,H3) = 7.1 Hz and 2J(C7a,H6) = 4.7 Hz.
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Figure 2. Part of the long-range 2D (δ, J) INEPT spectrum of 4d obtained upon selective excitation of the H-2 resonance; 1H- (in italics) and 13C-NMR chemical shifts in 4d.
Figure 2. Part of the long-range 2D (δ, J) INEPT spectrum of 4d obtained upon selective excitation of the H-2 resonance; 1H- (in italics) and 13C-NMR chemical shifts in 4d.
Molecules 14 03814 g002
Furthermore, the NMR spectra of N,N-diethylcarboxamides 5 and 6, respectively, two different signals sets for the ethyl moieties (Etcis, Ettrans, see Scheme 3) were found for each case. As expected, this indicates that there is restricted rotation around the amide bond under the recording conditions (CDCl3, ambient temperature).
In the IR spectra, the carbonyl C=O absorption from the ynones 2 appears in the range between 1,601 and 1,649 cm-1, and those from the thiopyranones 4 between 1,606 and 1,635 cm-1. Absorptions for the C≡C vibration in the IR spectra of compounds 2 appear from 2,196–2,202 cm-1.
As reported for related structures [48], the mass spectra of 4 exhibit a fragmentation behavior that is characterized by the loss of CO, a pathway that is also observed for ynones 2.

3. Conclusions

We have presented a widely applicable method for the preparation of heterocyclic annelated 2-phenylthiopyran-4-ones via a cross-coupling addition-cyclization approach starting from o-halo-heteroaroyl chlorides and phenylacetylene. Detailed NMR spectroscopic studies of the title compounds and their precursors were provided.

4. Experimental

4.1. General

Melting points were determined on a Reichert–Kofler hot-stage microscope and are uncorrected. Mass spectra were obtained on a Shimadzu QP 1000 instrument (EI, 70 eV), a Finnigan MAT 8230 instrument (EI, 70 eV, HRMS), and a Finnigan MAT 900S instrument (ESI, 4 kV, MeOH-acetonitrile). IR spectra (KBr unless otherwise stated) were recorded on a Perkin-Elmer FT-IR 1605 spectrophotometer or an ATI Mattson Genesis series FT-IR spectrophotometer. Elemental analyses (C, H, N and S) were performed at the Microanalytical Laboratory, University of Vienna, and were in good agreement (±0.4%) with the calculated values. 1H- and 13C-NMR spectra were recorded on a Varian UnityPlus 300 spectrometer at 28 °C (299.95 MHz for 1H, 75.43 MHz for 13C) or on a Bruker Avance 500 spectrometer at 293 K (500.13 MHz for 1H, 125.77 MHz for 13C). The center of the solvent (CDCl3) signal was used as an internal standard, which was related to TMS with δ 7.26 ppm (1H) and δ 77.0 ppm (13C). 15N-NMR spectra (50.68 MHz) and 19F-NMR spectra (470.56 MHz) were obtained on a Bruker Avance 500 spectrometer with a ‘directly’ detecting broadband observe probe (BBFO). The spectra were referenced against external nitromethane (15N) or against the absolute frequency scale (Ξ ratio, 19F). The digital resolution was 0.25 Hz/data point in the 1H spectra and 0.4 Hz/data point in the 13C-NMR spectra. Systematic names were generated with ACD/Name [49] according to the IUPAC recommendations and were checked manually [50]. For chromatographic separations, Kieselgel 60 (70–230 mesh, Merck) was used. Light petroleum had a boiling point of 40–65 °C.

4.2. Synthetic procedures

4.2.1. General procedure for the synthesis of o-halo(hetero)aroyl chlorides 1b–h

A suspension of the appropriate acid (2 mmol) in toluene (20 mL), DMF (5 drops) and SOCl2 (20 mmol, 2.38 g) was refluxed for 3 h or overnight. The solvent and excess SOCl2 were removed under reduced pressure. Additional toluene (4 × 5 mL) was added, and the solvent was removed under reduced pressure. The remaining acid chloride was immediately used in subsequent reaction steps (with no further purification).

4.2.2. General procedure for the synthesis of ynones 2a-h

The appropriate acid chloride 1 (2 mmol) was dissolved in dry CH2Cl2 (3 mL). Triethylamine (2 mL), phenylacetylene (1 mmol, 102 mg) and Pd(II) acetate (10 µmol, 2 mg) were added to the solution, which was stirred at room temperature under a N2 atmosphere (N2 balloon) for the indicated time. The solvent was removed under reduced pressure and water (20 mL) was added to the residue. The resulting solution was acidified with 5% HCl and extracted with CH2Cl2 or EtOAc (2 × 15 mL). The combined organic layers were washed with a saturated NaHCO3 solution and a saturated NaCl solution and were then dried over anhydrous Na2SO4. After removal of the solvent, the residue was purified by column chromatography through a silica gel column (eluent given below). An analytically pure sample was obtained by recrystallization from the appropriate solvent, which is indicated below.
1-(2-Chlorophenyl)-3-phenylprop-2-yn-1-one (2a1). Reaction time: 2.5 h. Eluent: toluene/light petroleum, 1:1 v/v. Yield: 209 mg, 87%; orange oil; [51] 1H-NMR (300 MHz): δ 8.08 (m, 1H, H-6), 7.65 (m, 2H, Ph H-2,6), 7.48 (m, 2H, H-3,4), 7.46 (m, 1H, Ph H-4), 7.41 (m, 2H, Ph H-3,5), 7.40 (m, 1H, H-5); 13C-NMR (75 MHz): δ 176.7 (C=O, 3J(CO,H6) = 5.3 Hz), 135.9 (C-1), 133.5 (C-2), 133.3 (C-4), 133.1 (Ph C-2,6), 132.4 (C-6), 131.5 (C-3), 130.9 (Ph C-4), 128.7 (Ph C-3,5), 126.8 (C-5), 120.1 (Ph C-1), 93.9 (COC≡C, 3J(C,Ph H2,6) = 5.5 Hz), 88.3 (COC≡C); IR (liquid film): 2196 (C≡C), 1649 (C=O) cm−1; MS m/z (%): 242/240 (M+, 14/40), 214/212 ([M − C=O]+, 25/72) 141/139 ([COC6H4Cl]+, 12/34), 129 ([COC≡CC6H5]+, 100), 101 ([C≡CC6H5]+, 14).
1-(2-Fluorophenyl)-3-phenylprop-2-yn-1-one (2a2). Reaction time: 45 min. Eluent: CH2Cl2/light petroleum, 1:1 v/v. Yield: 164 mg, 73%; light orange oil; [52] 1H-NMR (500 MHz): δ 8.11 (m, 1H, H-6), 7.67 (m, 2H, Ph H-2,6), 7.59 (m, 1H, H-4), 7.49 (m, 1H, Ph H-4), 7.42 (m, 2H, Ph H-3,5), 7.28 (m, 1H, H-5), 7.19 (m, 1H, H-3); 13C-NMR (125 MHz): δ 174.2 (C=O), 162.1 (C-2, 1J(C2,F2) = 261.7 Hz), 135.6 (C-4, 3J(C4,F2) = 9.2 Hz), 133.2 (Ph C-2,6), 131.8 (C-6), 130.9 (Ph C-4), 128.6 (Ph C-3,5), 125.6 (C-1, 2J(C1,F2) = 7.7 Hz), 124.2 (C-5, 4J(C5,F2) = 3.9 Hz), 120.1 (Ph C-1), 117.1 (C-3, 2J(C3,F2) = 21.9 Hz), 93.0 (COC≡C, J(C,F2) = 3.2 Hz), 88.5 (COC≡C); 19F-NMR (470 MHz): δ −111.3 (F-2); IR (liquid film): 2200 (C≡C), 1647 (C=O) cm−1; MS m/z (%): 224 (M+, 17), 196 ([M − C=O]+, 36), 129 ([COC≡CC6H5]+, 100), 123 ([COC6H4F]+, 84), 101 ([C≡CC6H5]+, 21), 74 (83).
1-(2-Bromothiophen-3-yl)-3-phenylprop-2-yn-1-one (2b). Reaction time: 19 h. Eluent: CH2Cl2/light petroleum, 3:2 v/v. Yield: 147 mg, 67%; whitish needles, mp 66–67 °C (EtOH/H2O); 1H- NMR (500 MHz): δ 7.65 (m, 2H, Ph H-2,6), 7.57 (d, 3J = 5.8 Hz, 1H, H-4), 7.48 (m, 1H, Ph H-4), 7.41 (m, 2H, Ph H-3,5), 7.28 (d, 3J = 5.8 Hz, 1H, H-5); 13C-NMR (125 MHz): δ 170.5 (C=O, 3J(CO,H4) = 2.0 Hz), 138.2 (C-3, 2J(C3,H4) = 4.5 Hz, 3J(C3,H5) = 8.4 Hz), 133.0 (Ph C-2,6), 130.9 (Ph C-4), 129.9 (C-4, 1J(C4,H4) = 173.4 Hz, 2J(C4,H5) = 3.8 Hz), 128.7 (Ph C-3,5), 126.0 (C-5, 1J(C5,H5) = 190.3 Hz, 2J(C5,H4) = 6.0 Hz), 120.3 (C-2, 3J(C2,H4) = 12.1 Hz, 3J(C2,H5) = 6.8 Hz), 120.0 (Ph C-1, 3J(Ph C1,Ph H3,5) = 8.5 Hz, 4J(Ph C1,Ph H4) = 1.3 Hz), 93.1 (COC≡C), 88.0 (COC≡C); IR: 2202 (C≡C), 1630 (C=O) cm−1; MS m/z (%): 292/290 (M+, 22/23), 264/262 ([M − C=O]+, 28/28), 139 (65), 129 ([COC≡CC6H5]+, 100), 101 ([C≡CC6H5]+, 16), 74 (79). Calcd. for C13H7BrOS: C, 53.63; H, 2.42; S, 11.01. Found: C, 53.31; H, 2.39; S, 10.92.
1-(4-Bromothiophen-3-yl)-3-phenylprop-2-yn-1-one (2c). Reaction time: 3 h. Eluent: CH2Cl2/light petroleum, 3:2 v/v. Yield: 148 mg, 25%; brownish oil; 1H-NMR (500 MHz): δ 8.42 (d, 4J = 3.5 Hz, 1H, H-2), 7.65 (m, 2H, Ph H-2,6), 7.49 (m, 1H, Ph H-4), 7.41 (m, 2H, Ph H-3,5), 7.36 (d, 4J = 3.5 Hz, 1H, H-5); 13C-NMR (125 MHz): δ 170.2 (C=O, 3J(CO,H2) = 3.6 Hz, 4J(CO,H5) = 0.6 Hz), 138.6 (C-3, 2J(C3,H2) = 3.2 Hz, 3J(C3,H5) = 7.9 Hz), 137.9 (C-2, 1J(C2,H2) = 189.5 Hz, 3J(C2,H5) = 5.3 Hz), 133.0 (Ph C-2,6), 130.9 (Ph C-4), 128.7 (Ph C-3,5), 126.1 (C-5, 1J(C5,H5) = 192.9 Hz, 3J(C5,H2) = 5.0 Hz), 119.9 (Ph C-1, 3J(Ph C1,Ph H3,5) = 8.6 Hz, 4J(Ph C1,Ph H4) = 1.3 Hz), 109.7 (C-4, 2J(C4,H5) = 0.9 Hz, 3J(C4,H2) = 11.2 Hz), 91.9 (COC≡C), 87.2 (COC≡C); IR (liquid film): 2189 (C≡C), 1640 (C=O) cm−1; MS m/z (%): 292/290 (M+, 2/2), 264/262 ([M − C=O]+, 2/1), 191/189 ([COC4H2SBr]+, 65/61), 129 ([COC≡CC6H5]+, 7), 101 ([C≡CC6H5]+, 1), 81 (100). Calcd. for C13H7BrOS: C, 53.63; H, 2.42; S, 11.01. Found: C, 53.38; H, 2.50; S, 10.67.
1-(3-Bromothiophen-2-yl)-3-phenylprop-2-yn-1-one (2d). Reaction time: 23 h. Eluent: CH2Cl2/light petroleum, 3:2 v/v. Yield: 134 mg, 46%; colorless needles, mp 74–77 °C (EtOH/H2O); 1H- NMR (500 MHz): δ 7.69 (m, 2H, Ph H2,6), 7.62 (d, 3J = 5.2 Hz, 1H, H-5), 7.50 (m, 1H, Ph H-4), 7.42 (m, 2H, Ph H-3,5), 7.18 (d, 3J = 5.2 Hz, 1H, H-4); 13C-NMR (125 MHz): δ 168.3 (C=O), 138.0 (C-2, 3J(C2,H4) = 7.4 Hz, 3J(C2,H5) = 4.8 Hz), 134.0 (C-4, 1J(C4,H4) = 176.5 Hz, 2J(C4,H5) = 4.1 Hz), 133.6 (C-5, 1J(C5,H5) = 188.1 Hz, 2J(C5,H4) = 6.1 Hz), 133.1 (Ph C-2,6), 131.0 (Ph C-4), 128.7 (Ph C-3,5), 119.9 (Ph C-1), 116.4 (C-3, 2J(C3,H4) = 2.4 Hz, 3J(C3,H5) = 12.2 Hz), 94.1 (COC≡C), 87.3 (COC≡C); IR: 2198 (C≡C), 1627 (C=O) cm−1; MS m/z (%): 292/290 (M+, 25/22), 264/262 ([M − C=O]+, 52/47), 139 (95), 129 ([COC≡CC6H5]+, 97), 101 ([C≡CC6H5]+, 22), 84 (73), 74 (77), 43 (100). Calcd. for C13H7BrOS: C, 53.63; H, 2.42; S, 11.01. Found: C, 53.63; H, 4.00; S, 10.85. HRMS Calcd. for C13H7BrOS: 289.9401. Found: 289.9403.
1-(3-Chloro-1-benzo[b]thiophen-2-yl)-3-phenylprop-2-yn-1-one (2e). Reaction time: 2.5 h. Eluent: toluene. Yield: 213 mg, 72%; light tan crystals, mp 117–120 °C (MeOH); 1H-NMR (500 MHz): δ 8.03 (d, 3J = 8.0 Hz, 1H, H-4), 7.85 (d, 3J = 8.1 Hz, 1H, H-7), 7.72 (m, 2H, Ph H-2,6), 7.57 (m, 1H, H-6), 7.52 (m, 2H, H-5, Ph H-4), 7.45 (m, 2H, Ph H-3,5); 13C-NMR (125 MHz): δ 169.3 (C=O), 139.3 (C-7a), 137.6 (C-3a), 136.4 (C-2), 133.2 (Ph C-2,6), 131.2 (Ph C-4), 129.0 (C-6), 128.7 (Ph C-3,5), 126.9 (C-3, 3J(C3,H4) = 7.7 Hz), 125.7 (C-5), 124.4 (C-4), 122.9 (C-7), 119.9 (Ph C-1), 95.1 (COC≡C, 3J(C,Ph H2,6) = 5.4 Hz), 88.0 (COC≡C); IR: 2199 (C≡C), 1601 (C=O) cm−1; MS m/z (%): 298/296 (M+, 27/68), 270/268 ([M − C=O]+, 40/100), 129 ([COC≡CC6H5]+, 100), 101 ([C≡CC6H5]+, 14). Calcd. for C17H9ClOS•0.2 H2O: C, 67.98; H, 3.15. Found: C, 68.11; H, 2.82.
1-(2-Chloropyridin-3-yl)-3-phenylprop-2-yn-1-one (2f). Reaction time: 2.5 h. Eluent: CH2Cl2/EtOAc, 20:1 v/v. Yield: 123 mg, 51%; yellowish-brown crystals, mp 69–71 °C (MeOH); 1H- NMR (500 MHz): δ 8.56 (dd, 3J(H5,H6) = 4.7 Hz, 4J = 1.9 Hz, 1H, H-6), 8.34 (dd, 3J = 7.7 Hz, 4J = 1.9 Hz, 1H, H-4), 7.65 (m, 2H, Ph H-2,6), 7.51 (m, 1H, Ph H-4), 7.42 (m, 3H, H-5, Ph H-3,5); 13C-NMR (125 MHz): δ 175.5 (C=O, 3J(CO,H4) = 5.3 Hz), 152.3 (C-6, 1J(C6,H6) = 183.7 Hz, 2J(C6,H5) = 3.8 Hz, 3J(C6,H4) = 8.2 Hz), 149.5 (C-2, 3J(C2,H4) = 8.8 Hz, 3J(C2,H6) = 13.8 Hz, 4J(C2,H5) = 1.5Hz), 140.7 (C-4, 1J(C4,H4) = 166.2 Hz, 2J(C4,H5) = 1.9 Hz, 3J(C4,H6) = 6.7 Hz), 132.6 (C-3), 133.2 (Ph C-2,6), 131.3 (Ph C-4), 128.8 (Ph C-3,5), 122.4 (C-5, 1J(C5,H5) = 168.2 Hz, 2J(C5,H6) = 8.2 Hz), 119.5 (Ph C-1, 3J(Ph C1,Ph H3,5) = 8.6 Hz, 4J(Ph C1,Ph H4) = 1.4 Hz), 95.7 (COC≡C, 3J(C,Ph H2,6) = 5.3 Hz), 87.9 (COC≡C); 15N-NMR (50 MHz): δ −70.3 (N-1); IR: 2199 (C≡C), 1636 (C=O) cm−1; MS m/z (%): 243/241 (M+, 6/15), 215/213 ([M − C=O]+, 6/21), 129 ([COC≡CC6H5]+, 100), 101 ([C≡CC6H5]+, 13). Calcd. for C14H8ClNO: C, 69.58; H, 3.34; N, 5.80. Found: C, 69.59; H, 3.16; N, 5.67.
1-(3-Chloropyridin-4-yl)-3-phenylprop-2-yn-1-one (2g). Reaction time: 23 h. Eluent: CH2Cl2/EtOAc, 20:1 v/v. Yield: 70 mg, 19%; brown crystals, mp 77–79 °C (MeOH/H2O, 5:1 v/v); 1H- NMR (500 MHz): δ 8.76 (s, 1H, H-2), 8.68 (d, 3J = 4.9 Hz, 1H, H-6), 7.81 (d, 3J = 4.9 Hz, 1H, H-5), 7.65 (m, 2H, Ph H-2,6), 7.52 (m, 1H, Ph H-4), 7.43 (m, 2H, Ph H-3,5); 13C-NMR (125 MHz): δ 175.3 (C=O), 151.6 (C-2, 1J(C2,H2) = 188.0 Hz, 3J(C2,H6) = 11.4 Hz, 4J(C2,H5) = 1.0 Hz), 148.4 (C-6, 1J(C6,H6) = 183.6 Hz, 2J(C6,H5) = 2.3 Hz, 3J(C6,H2) = 11.6 Hz), 141.8 (C-4, 2J(C4,H5) = not resolved, 3J(C4,H2) = 4.9 Hz, 3J(C4,H6) = 6.9 Hz), 133.3 (Ph C-2,6), 131.6 (Ph C-4), 129.3 (C-3), 128.8 (Ph C-3,5), 124.0 (C-5, 1J(C5,H5) = 167.1 Hz, 2J(C5,H6) = 9.7 Hz), 119.3 (Ph C-1, 3J(Ph C1,Ph H3,5) = 8.5 Hz, 4J(Ph C1,Ph H4) = 1.4 Hz), 96.2 (COC≡C, 3J(C,Ph H2,6) = 5.4 Hz), 87.8 (COC≡C); IR: 2197 (C≡C), 1641 (C=O) cm−1; MS m/z (%): 243/241 (M+, 4/12), 215/213 ([M − C=O]+, 4/8), 129 ([COC≡CC6H5]+, 100), 101 ([C≡CC6H5]+, 11). Calcd. for C14H8ClNO•0.2 H2O: C, 68.56; H, 3.45; N, 5.71. Found: C, 68.69; H, 3.25; N, 5.63.
1-(2-Chloroquinolin-3-yl)-3-phenylprop-2-yn-1-one (2h). Reaction time: 200 min. Eluent: light petroleum/EtOAc, 4:1 v/v. Yield: 181 mg, 62%; brownish-yellow crystals, mp 100–101 °C (MeOH); 1H-NMR (500 MHz): δ 8.87 (s, 1H, H-4), 8.08 (dd, 3J = 8.5 Hz, 4J = 1.1 Hz, 1H, H-8), 7.97 (dd, 3J = 8.1 Hz, 4J = 1.4 Hz, 1H, H-5), 7.88 (m, 3J(H7,H6) = 7.0 Hz, 3J(H7,H8) = 8.5 Hz, 4J = 1.4 Hz, 1H, H-7), 7.68 (m, 2H, Ph H-2,6), 7.66 (m, 1H, H-6), 7.51 (m, 1H, Ph H-4), 7.44 (m, 2H, Ph H-3,5); 13C-NMR (125 MHz): δ 175.3 (C=O, 3J(CO,H4) = 5.7 Hz), 148.4 (C-8a), 147.0 (C-2, 3J(C2,H4) = 9.7 Hz), 142.7 (C-4, 1J(C4,H4) = 164.4 Hz, 3J(C4,H5) = 4.6 Hz), 133.2 (C-7, Ph C-2,6), 131.3 (Ph C-4), 130.2 (C-3), 128.9 (C-5), 128.8 (Ph C-3,5), 128.5 (C-8), 128.0 (C-6), 126.0 (C-4a), 119.7 (Ph C-1, 3J(Ph C1,Ph H3,5) = 8.5 Hz, 4J(Ph C1,Ph H4) = 1.3 Hz), 95.2 (COC≡C, 3J(C,Ph H2,6) = 5.3 Hz, 4J(C,Ph H3,5) = 1.0 Hz), 88.0 (COC≡C); 15N-NMR (50 MHz): δ −78.4 (N-1); IR: 2197 (C≡C), 1632 (C=O) cm−1; MS m/z (%): 293/291 (M+, 6/15), 265/263 ([M − C=O]+, 8/24), 239 (41), 129 ([COC≡CC6H5]+, 90), 101 ([C≡CC6H5]+, 45), 43 (100). Calcd. for C18H10ClNO•0.4 H2O: C, 72.32; H, 3.64; N, 4.69. Found: C, 72.27; H, 3.37; N, 5.01.

4.2.3. General procedure for the synthesis of thiopyranones 4a–h

A suspension of NaSH hydrate (~60%, 1.2 mmol, 112 mg) was refluxed in EtOH (20 mL) until a cloudy solution was formed. Ynone 2 (0.4 mmol) in EtOH (2 mL) was then added to the solution, which was refluxed for the indicated time. The solvent was removed under reduced pressure and water (20 mL) was added to the residue. The resulting solution was acidified with 5% HCl and extracted with CH2Cl2 (2 × 15 mL). The combined organic layers were washed with a saturated NaHCO3 solution and a saturated NaCl solution. They were then dried over anhydrous Na2SO4. After removal of the solvent, the residue was purified by column chromatography through a silica gel (eluent as indicated below). An analytically pure sample was obtained by recrystallization from an appropriate solvent.
2-Phenyl-4H-thiochromen-4-one (4a). Reaction time: 4 h. Eluent: CH2Cl2/EtOAc, 15:1 v/v. Yield: 131 mg, 54%; beige needles, mp 121–123 °C (MeOH) (lit. [18] mp 124–126 °C); 1H= NMR (500 MHz): δ 8.54 (dd, 1H, H-5), 7.68 (m, 2H, Ph H-2,6), 7.65 (dd, 1H, H-8), 7.62 (dt, 1H, H-7), 7.54 (dt, 1H, H-6), 7.51 (m, 1H, Ph H-4), 7.50 (m, 2H, Ph H-3,5), 7.24 (s, 1H, H-3); 13C-NMR (125 MHz): δ 180.8 (C-4), 153.0 (C-2), 137.6 (C-8a), 136.5 (Ph C-1), 131.6 (C-7), 130.8 (C-4a, Ph C-4), 129.2 (Ph C-3,5), 128.5 (C-5), 127.7 (C-6), 126.9 (Ph C-2,6), 126.4 (C-8), 123.4 (C-3, 1J(C3,H3) = 163.6 Hz); IR: 1620 (C=O) cm−1; MS m/z (%): 238 (M+, 92), 210 ([M − C=O]+, 100), 136 ([COC6H4S]+, 53), 108 ([C6H4S]+, 28).
6-Phenyl-4H-thieno[2,3-b]thiopyran-4-one (4b). Reaction time: 100 min. Eluent: CH2Cl2/EtOAc, 5:1 v/v. Yield: 20 mg, 50%; whitish powder, mp 115–117 °C (MeOH); 1H-NMR (500 MHz): δ 7.78 (d, 3J = 5.3 Hz, 1H, H-3), 7.62 (m, 2H, Ph H-2,6), 7.50 (m, 1H, Ph H-4), 7.49 (m, 2H, Ph H-3,5), 7.46 (d, 3J = 5.3 Hz, 1H, H-2), 7.20 (s, 1H, H-5); 13C-NMR (125 MHz): δ 177.1 (C-4, 2J(C4,H5) = 1.2 Hz, 3J(C4,H3) = 1.3 Hz), 151.5 (C-6, 2J(C6,H5) = 3.4 Hz), 144.3 (C-7a, 3J(C7a,H2) = 6.7 Hz, 3J(C7a,H3) = 10.0 Hz), 137.5 (C-3a, 2J(C3a,H3) = 4.7 Hz, 3J(C3a,H2) = 9.9 Hz, 3J(C3a,H5) = 3.7 Hz), 136.1 (Ph C-1, 3J(Ph C1,H5) = 5.4 Hz), 130.7 (Ph C-4), 129.3 (Ph C-3,5), 127.0 (Ph C-2,6), 125.5 (C-3, 1J(C3,H3) = 174.8 Hz, 2J(C3,H2) = 4.4 Hz, 4J(C3,H5) = 1.0 Hz), 125.3 (C-2, 1J(C2,H2) = 189.6 Hz, 2J(C2,H3) = 7.5 Hz), 125.0 (C-5, 1J(C5,H5) = 163.3 Hz); IR: 1606 (C=O) cm−1; MS m/z (%): 244 (M+, 100), 216 ([M − C=O]+, 31), 142 ([COC4H2S2]+, 97), 120 ([COCH=CC6H5]+, 69), 114 ([C4H2S2]+, 38), 101 ([C=CC6H5]+, 27). Calcd. for C13H8OS2: C, 63.90; H, 3.30. Found: C, 63.57; H, 3.27.
2-Phenyl-4H-thieno[3,4-b]thiopyran-4-one (4c). Reaction time: 22.5 h. Eluent: CH2Cl2/EtOAc, 5:1 v/v. Yield: 28 mg, 34%; brownish needles, mp 160–162 °C (MeOH/H2O); 1H-NMR (500 MHz): δ 8.51 (d, 4J = 3.4 Hz, 1H, H-5), 7.66 (m, 2H, Ph H-2,6), 7.52 (d, 3J = 3.4 Hz, 1H, H-7), 7.49 (m, 1H, Ph H-4), 7.48 (m, 2H, Ph H-3,5), 6.99 (s, 1H, H-3); 13C-NMR (125 MHz): δ 178.2 (C-4, 2J(C4,H3) = 1.1 Hz, 3J(C4,H5) = 2.2 Hz, 4J(C4,H7) = 1.1 Hz), 153.3 (C-2, 2J(C2,H3) = 3.1 Hz), 136.7 (Ph C-1, 3J(Ph C1,H3) = 5.5 Hz), 134.7 (C-4a, 2J(C4a,H5) = 3.2 Hz, 3J(C4a,H3) = 3.8 Hz, 3J(C4a,H7) = 7.8 Hz), 131.4 (C-7a, 2J(C7a,H7) = 2.8 Hz, 3J(C7a,H5) = 9.8 Hz), 130.8 (Ph C-4), 129.7 (C-5, 1J(C5,H5) = 191.8 Hz, 3J(C5,H7) = 4.9 Hz, 4J(C5,H3) = 1.3 Hz), 129.2 (Ph C-3,5), 127.0 (Ph C-2,6), 122.1 (C-3, 1J(C3,H3) = 163.6 Hz), 119.2 (C-7, 1J(C7,H7) = 189.3 Hz, 3J(C7,H5) = 5.7 Hz); IR: 1612 (C=O) cm−1; MS m/z (%): 244 (M+, 48), 216 ([M − C=O]+, 16), 142 ([COC4H2S2]+, 100), 114 ([C4H2S2]+, 36), 82 ([C4H2S]+, 22). Calcd. for C13H8OS2: C, 63.90; H, 3.30. Found: C, 62.82; H 3.28. HRMS (ESI) Calcd. for C13H9OS2 [M+H]: 245.0095. Found: 245.0100.
5-Phenyl-7H-thieno[3,2-b]thiopyran-7-one (4d). Reaction time: 1 h. Eluent: CH2Cl2/EtOAc, 5:1 v/v. Yield: 80 mg, 87%; brownish powder, mp 82–84 °C (EtOH/H2O) (lit. [24] mp 80 °C); 1H-NMR (500 MHz): δ 7.85 (d, 3J = 5.3 Hz, 1H, H-2), 7.65 (m, 2H, Ph H-2,6), 7.51 (m, 3H, Ph H-3,4,5), 7.35 (d, 3J = 5.3 Hz, 1H, H-3), 7.21 (s, 1H, H-6); 13C-NMR (125 MHz): δ 176.2 (C-7, 2J(C7,H6) = 1.1 Hz, 4J(C7,H2) = 1.1 Hz, 4J(C7,H3) = 1.1 Hz), 152.8 (C-5, 2J(C5,H6) = 3.1 Hz), 139.0 (C-3a, 2J(C3a,H3) = 4.4 Hz, 3J(C3a,H2) = 11.2 Hz), 137.2 (C-7a, 3J(C7a,H2) = 5.9 Hz, 3J(C7a,H3) = 7.1 Hz, 3J(C7a,H6) = 4.7 Hz), 136.4 (Ph C-1, 3J(Ph C1,H6) = 5.4 Hz), 133.2 (C-2, 1J(C2,H2) = 186.6 Hz, 2J(C2,H3) = 6.0 Hz), 130.7 (Ph C-4), 129.3 (Ph C-3,5), 127.2 (Ph C-2,6), 125.3 (C-3, 1J(C3,H3) = 173.4 Hz, 2J(C3,H2) = 4.8 Hz), 123.6 (C-6, 1J(C6,H6) = 163.9 Hz); MS m/z (%): 244 (M+, 46), 243 ([M − H]+, 21), 216 ([M − C=O]+, 16), 142 ([COC4H2S2]+, 94), 114 ([C4H2S2]+, 33), 102 ([CH=CC6H5]+, 19), 82 ([C4H2S]+, 20), 69 (100).
2-Phenyl-4H-thiopyrano[3,2-b][1]benzothiophen-4-one (4e). Reaction time: 70 min. Eluent: CH2Cl2/EtOAc, 15:1 v/v. Yield: 96 mg, 82%; colorless crystals, mp 166–167 °C (MeOH/EtOAc, 2:1 v/v) (lit. [25] mp 177 °C); 1H-NMR (500 MHz): δ 8.00 (m, 1H, H-9), 7.99 (m, 1H, H-6), 7.71 (m, 2H, Ph H-2,6), 7.59 (m, 1H, H-7), 7.54 (m, 3H, Ph H-3,4,5), 7.53 (m, 1H, H-8), 7.32 (s, 1H, H-3); 13C-NMR (125 MHz): δ 177.0 (C-4, 2J(C4,H3) = 1.1 Hz), 152.1 (C-2, 2J(C2,H3) = 3.1 Hz), 140.7 (C-5a), 137.3 (C-4a, 3J(C4a,H3) = 4.6 Hz), 136.3 (Ph C-1, 3J(Ph C1,H3) = 5.3 Hz), 136.2 (C-9a), 135.4 (C-9b, 3J(C9b,H9) = 3.9 Hz), 130.8 (Ph C-4), 129.4 (Ph C-3,5), 128.6 (C-7, 1J(C7,H7) = 162.0 Hz, 3J(C7,H9) = 7.8 Hz), 127.2 (Ph C-2,6), 125.3 (C-8, 1J(C8,H8) = 162.5 Hz, 3J(C8,H6) = 7.6 Hz), 124.7 (C-3, 1J(C3,H3) = 163.9 Hz), 123.8 (C-6, 1J(C6,H6) = 164.8 Hz, 2J(C6,H7) = 1.5 Hz, 3J(C6,H8) = 8.0 Hz, 4J(C6,H9) = 1.5 Hz), 122.5 (C-9, 1J(C9,H9) = 161.1 Hz, 2J(C9,H8) = 1.4 Hz, 3J(C9,H7) = 8.1 Hz, 4J(C9,H6) = 1.4 Hz); IR: 1618 (C=O) cm−1; MS m/z (%): 294 (M+, 32), 266 ([M–C=O]+, 34), 164 ([C8H4S2]+, 25), 132 ([C8H4S]+, 29), 120 (43), 68 (100). Calcd. for C17H10OS2•0.1 H2O: C, 68.94; H, 3.47; S, 21.65. Found: C, 68.91; H, 3.45; S, 21.26.
2-Phenyl-4H-thiopyrano[2,3-b]pyridin-4-one (4f). Reaction time: 1.5 h. Eluent: CH2Cl2/EtOAc, 15:1 v/v. Yield: 36 mg, 93%; luminous yellow needles, mp 114–117 °C (MeOH) (lit. [19] mp 113–116 °C); 1H-NMR (300 MHz): δ 8.81 (dd, 3J = 4.5 Hz, 4J = 1.9 Hz, 1H, H-7), 8.77 (dd, 3J = 8.1 Hz, 4J = 1.9 Hz, 1H, H-5), 7.71 (m, 2H, Ph H-2,6), 7.53 (m, 3H, Ph H-3,4,5), 7.50 (dd, 3J(H6,H7) = 4.5 Hz, 3J(H6,H5) = 8.1 Hz, 1H, H-6), 7.26 (s, 1H, H-3); 13C-NMR (75 MHz): δ 181.3 (C-4, 3J(C4,H5) = 3.5 Hz), 159.1 (C-8a, 3J(C8a,H5) = 6.5 Hz, 3J(C8a,H7) = 14.0 Hz), 154.7 (C-2), 152.8 (C-7, 1J(C7,H7) = 181.7 Hz, 2J(C7,H6) = 3.8 Hz, 3J(C7,H5) = 7.8 Hz), 136.7 (C-5, 1J(C5,H5) = 168.2 Hz, 2J(C5,H6) not resolved, 3J(C5,H7) = 6.2 Hz), 136.3 (Ph C-1), 131.1 (Ph C-4), 129.4 (Ph C-3,5), 128.1 (C-4a), 127.0 (Ph C-2,6), 123.6 (C-3, 1J(C3,H3) = 164.7 Hz), 122.9 (C-6, 1J(C6,H6) = 167.0 Hz, 2J(C6,H5) not resolved, 2J(C6,H7) = 8.2 Hz); 15N-NMR (50 MHz): δ −76.8 (N-8); IR: 1630 (C=O) cm−1; MS m/z (%): 239 (M+, 100), 211 ([M − C=O]+, 99), 137 ([COC5H3NS]+, 33), 109 ([C5H3NS]+, 57), 105 ([COC5H3N]+, 32), 102 ([CH=CC6H5]+, 33). Calcd. for C14H9NOS: C, 70.27; H, 3.79; N, 5.85. Found: C, 70.26; H, 4.04; N, 5.75.
2-Phenyl-4H-thiopyran[2,3-c]pyridin-4-one (4g). Reaction time: 1.5 h. Eluent: CH2Cl2/EtOAc, 5:1 v/v. Yield: 21 mg, 44%; flat brownish prisms, mp 153–154 °C (EtOH/H2O); 1H-NMR (500 MHz): δ 9.02 (s, 1H, H-8), 8.73 (d, 3J = 5.3 Hz, 1H, H-6), 8.27 (d, 3J = 5.3 Hz, 1H, H-5), 7.69 (m, 2H, Ph H-2,6), 7.53 (m, 1H, Ph H-4), 7.52 (m, 2H, Ph H-3,5), 7.27 (s, 1H, H-3); 13C-NMR (125 MHz): δ 179.5 (C-4, 2J(C4,H3) = 1.0 Hz, 3J(C4,H5) = 3.6 Hz, 4J(C4,H8) = 1.6 Hz), 154.0 (C-2, 2J(C2,H3) = 2.5 Hz), 148.8 (C-8, 1J(C8,H8) = 183.4 Hz, 3J(C8,H6) = 11.1 Hz, 4J(C8,H5) = 0.8 Hz), 147.8 (C-6, 1J(C6,H6) = 182.7 Hz, 2J(C6,H5) = 3.2 Hz, 3J(C6,H8) = 11.6 Hz), 136.1 (Ph C-1, 3J(Ph C1,H3) = 5.5 Hz), 135.7 (C-4a, 2J(C4a,H5) not resolved, 3J(C4a,H3) = 3.7 Hz, 3J(C4a,H6) = 6.7 Hz, 3J(C4a,H8) = 5.1 Hz), 133.2 (C-8a, 2J(C8a,H8) = 7.9 Hz, 3J(C8a,H5) = 6.5 Hz, 4J(C8a,H6) = 1.8 Hz), 131.3 (Ph C-4), 129.4 (Ph C-3,5), 127.0 (Ph C-2,6), 123.9 (C-3, 1J(C3,H3) = 164.5 Hz), 120.6 (C-5, 1J(C5,H5) = 168.9 Hz, 2J(C5,H6) = 9.0 Hz, 4J(C5,H3) = 0.8 Hz, 4J(C5,H8) = 1.7 Hz); 15N-NMR (50 MHz): δ −60.0 (N-7); IR: 1635 (C=O) cm−1; MS m/z (%): 239 (M+, 100), 211 ([M − C=O]+, 77), 149 (49), 139 (28), 137 ([COC5H3NS]+, 66), 109 ([C5H3NS]+, 53), 105 ([COC5H3N]+, 20), 102 ([CH=CC6H5]+, 41), 81 (98). Calcd. for C14H9NOS: C, 70.27; H, 3.79; N, 5.85; S, 13.40. Found: C, 70.28; H, 4.02; N, 5.69; S, 13.21. HRMS Calcd. for C14H9NOS: 239.0405. Found: 239.0402.
2-Phenyl-4H-thiopyrano[2,3-b]quinolin-4-one (4h). Reaction time: 100 min. Eluent: CH2Cl2/EtOAc, 20:1 v/v. Yield: 77 mg, 67%; off-white needles, mp 208–210 °C (CH2Cl2/EtOAc, 5:1 v/v); 1H-NMR (500 MHz): δ 9.30 (s, 1H, H-5), 8.09 (d, 3J = 8.6 Hz, 1H, H-9), 8.04 (d, 3J = 8.1 Hz, 1H, H-6), 7.88 (m, 1H, H-8), 7.74 (m, 2H, Ph H-2,6), 7.62 (m, 1H, H-7), 7.54 (m, 3H, Ph H-3,4,5), 7.23 (s, 1H, H-3); 13C-NMR (125 MHz): δ 182.0 (C-4, 2J(C4,H3) = 0.7 Hz, 3J(C4,H5) = 4.1 Hz), 157.1 (C-10a, 3J(C10a,H5) = 8.1 Hz), 155.1 (C-2), 149.2 (C-9a), 138.6 (C-5, 1J(C5,H5) = 166.4 Hz, 3J(C5,H6) = 4.7 Hz), 136.4 (Ph C-1), 133.1 (C-8), 131.2 (Ph C-4), 129.7 (C-6), 129.4 (Ph C-3,5), 128.1 (C-9), 127.2 (C-7), 127.0 (Ph C-2,6), 126.9 (C-5a), 125.1 (C-4a), 122.1 (C-3, 1J(C3,H3) = 164.8 Hz); 15N-NMR (50 MHz): δ −83.8 (N-10); IR: 1631 (C=O) cm−1; MS m/z (%): 289 (M+, 91), 261 ([M − C=O]+, 88), 181 (46), 159 ([C9H5NS]+, 39), 130 ([COCH=CC6H5]+, 77), 101 ([C=CC6H5]+, 44), 75 (82), 68 (100). Calcd. for C18H11NOS•0.2 H2O: C, 73.80; H, 3.92; N, 4.78. Found: C, 73.85; H, 3.71; N, 4.77.

4.2.4. Preparation of N,N-diethyl-3-fluoropyridine-2-carboxamide (5)

Under the conditions given for the synthesis of compounds 2, reaction of 1i (2 mmol, 319 mg) with phenylacetylene (1 mmol, 102 mg), Et3N (2 mL) and Pd(II) acetate (10 µmol, 2 mg) for 26 h resulted in formation of compound 5 after purification by column chromatography (eluent: EtOAc). Yield: 131 mg, 33%; brown oil; 1H-NMR (500 MHz): δ 8.42 (dd, 3J = 4.6 Hz, 4J = 1.1 Hz, 5J(H6,F3) = 1.4 Hz, 1H, H-6), 7.47 (dd, 3J(H4, H5) = 8.5 Hz, 3J(H4,F3) = 8.9 Hz, 4J = 1.1 Hz, 1H, H-4), 7.35 (m, 3J(H5,H6) = 4.6 Hz, 3J(H5,H4) = 8.5 Hz, 4J(H5,F3) = 4.2 Hz, 1H, H-5), 3.58 (q, 3J = 7.1 Hz, 2H, N-CH2 cis), 3.20 (q, 3J = 7.1 Hz, 2H, N-CH2 trans), 1.27 (t, 3J = 7.1 Hz, 3H, CH3 cis), 1.10 (t, 3J = 7.1 Hz, 3H, CH3 trans); 13C-NMR (125 MHz): δ 164.7 (C=O, 3J(CO,F3) = 3.1 Hz), 155.8 (C-3, 1J(C3,F3) = 259.1 Hz, 2J(C3,H4) = 4.8 Hz, 3J(C3,H5) = 9.6 Hz, 4J(C3,H6) = 1.9 Hz), 145.2 (C-6, 1J(C6,H6) = 182.3 Hz, 2J(C6,H5) = 2.7 Hz, 3J(C6,H4) = 7.3 Hz, 4J(C6,F3) = 5.0 Hz), 144.0 (C-2, 2J(C2,F3) = 18.0 Hz, 3J(C2,H4) = 3.8 Hz, 3J(C2,H6) = 12.2 Hz, 4J(C2,H5) = 1.5 Hz), 125.1 (C-5, 1J(C5,H5) = 167.2 Hz, 2J(C5,H4) = 2.0 Hz, 2J(C5,H6) = 9.4 Hz, 3J(C5,F3) = 3.8 Hz), 123.9 (C-4, 1J(C4,H4) = 167.4 Hz, 2J(C4,F3) = 18.4 Hz, 3J(C4,H6) = 7.2 Hz), 42.8 (N-CH2 trans, 1J = 135.2 Hz, 2J(CH2,CH3) = 4.2 Hz), 39.4 (N-CH2 cis, 1J = 136.5 Hz, 2J(CH2,CH3) = 4.2 Hz), 14.0 (CH3 trans, 1J = 127.1 Hz, 2J(CH3,CH2) = 3.1 Hz), 12.8 (CH3 cis, 1J = 127.2 Hz, 2J(CH3,CH2) = 3.4 Hz); 15N-NMR (50 MHz): δ −65.8 (N-1), −248.9 (CONR2); 19F-NMR (470 MHz): δ −124.3 (F-3, 3J(F3,H4) = 8.9 Hz, 4J(F3,H5) = 4.2 Hz, 5J(F3,H6) = 1.4 Hz); IR: 1643 (C=O) cm−1; MS m/z (%): 196 (M+, 7), 124 ([M − N(Et)2]+, 65), 97 ([C5H3NF]+, 55), 72 ([N(Et)2]+, 100), 44 (63). Calcd. for C10H13FN2O•0.2 H2O: C, 60.11; H, 6.76; N, 14.02. Found: C, 60.28; H, 6.59; N, 13.90.

4.2.5. Preparation of 3-chloro-N,N-diethylquinoxaline-2-carboxamide (6)

Under the conditions given for synthesis of compounds 2, reaction of 1j (2 mmol, 455 mg) with phenylacetylene (1 mmol, 102 mg), Et3N (2 mL) and Pd(II) acetate (10 µmol, 2 mg) for 20 h resulted in formation of compound 6 after purification by column chromatography (eluent: CH2Cl2/EtOAc, 5:1 v/v.). Yield: 256 mg, 49%; brownish needles, mp 91–93 °C (MeOH); 1H-NMR (500 MHz): δ 8.10 (m, 1H, H-8), 8.03 (m, 1H, H-5), 7.83 (m, 1H, H-6), 7.80 (m, 1H, H-7), 3.65 (q, 3J = 7.2 Hz, 2H, N-CH2 cis), 3.20 (q, 3J = 7.1 Hz, 2H, N-CH2 trans), 1.34 (t, 3J = 7.2 Hz, 3H, CH3 cis), 1.16 (t, 3J = 7.1 Hz, 3H, CH3 trans); 13C-NMR (125 MHz): δ 164.8 (C=O), 149.1 (C-3), 143.8 (C-2), 141.6 (C-4a), 140.0 (C-8a), 131.6 (C-6), 130.8 (C-7), 129.2 (C-8), 128.3 (C-5), 42.9 (N-CH2 trans), 39.5 (N-CH2 cis), 13.8 (CH3 trans), 12.5 (CH3 cis); 15N-NMR (50 MHz): δ –52.1 (N-1), −63.0 (N-4), −249.2 (CONR2); IR: 1635 (C=O) cm−1; MS m/z (%): 265/263 (M+, 0.5/1.5), 191 ([M − N(Et)2]+, 3), 165/163 ([C8H4N2Cl]+, 7/18), 128 ([C8H4N2]+, 5), 72 ([N(Et)2]+, 100). Calcd. for C13H14ClN3O: C, 59.21; H, 5.35; N, 15.93. Found: C, 59.43; H, 5.42; N, 15.99.

4.2.6. Preparation of (2Z,2'Z)-3,3'-sulfanediylbis[1-(2-chlorophenyl)-3-phenylprop-2-en-1-one] (7)

Ynone 2a1 (0.5 mmol, 120 mg) in EtOH (2 mL) was added to a suspension of NaSH hydrate (~60%, 1.3 mmol, 121 mg) in EtOH (20 mL). The resulting solution was stirred at room temperature for 30 min, and then processed as described in the preparation of compounds 4. The residue was purified by column chromatography through silica gel (eluent: CH2Cl2). Yield: 48 mg, 19%; yellow powder, mp 161–164 °C (EtOH); 1H-NMR (300 MHz): δ 7.65 (m, 2H, H-6), 7.43 (m, 2H, H-3), 7.42 (m, 2H, H-4), 7.38 (m, 2H, H-5), 7.18 (m, 2H, Ph H-4), 7.05 (m, 4H, Ph H-3,5), 6.97 (m, 4H, Ph H-2,6), 6.92 (s, 2H, COCH=C); 13C-NMR (75 MHz): δ 189.7 (C=O), 155.4 (COCH=C), 140.6 (Ph C-1), 139.7 (C-1), 131.9 (C-4), 131.4 (C-2), 130.5 (C-6), 130.2 (C-3), 128.9 (Ph C-4), 128.3 (Ph C-2,6), 128.0 (Ph C-3,5), 127.7 (COCH=C, 1J = 161.5 Hz), 127.1 (C-5); IR: 1638 (C=O) cm−1; MS m/z (%): 516/514 (M+, 0.3/0.4), 275/273 ([M − C15H10ClO]+, 13/33), 238 (19), 149 ([COC(S)C6H5]+, 80), 141/139 ([COC6H4Cl]+, 37/100), 113/111 ([C6H4Cl]+, 29/49), 105 (38), 85 ([COCH=CS]+, 32), 77 ([C6H5]+, 33), 57 (83). HRMS (ESI) Calcd. for C30H21Cl2O2S [M + H]: 515.0639. Found: 515.0642.

4.2.7. Preparation of (2Z)-1-(2-chlorophenyl)-3-(methylamino)-3-phenylprop-2-en-1-one (10)

Ethanolic methylamine-solution (33 wt%, 6 mL, 48 mmol) was added to a solution of ynone 2a1 (0.5 mmol, 120 mg) in pyridine (0.4 mL) and H2O (3 drops). The solution was refluxed for 1 h. The solvent was then removed under reduced pressure and water (20 mL) was added to the residue. The resulting solution was adjusted to pH 5 with 5% HCl and extracted with CH2Cl2 (2 × 15 mL). The combined organic layers were washed with a saturated NaHCO3 solution and a saturated NaCl solution and then dried over anhydrous Na2SO4. After removal of the solvent, the residue was purified by column chromatography through silica gel (eluent: CH2Cl2/EtOAc, 20:1 v/v.), which produced 10 as a slowly crystallizing oil. Yield: 99 mg, 73%; pale orange solid, mp 77–80 °C; 1H-NMR (500 MHz): δ 11.18 (broad, 1H, N-H), 7.49 (m, 1H, H-6), 7.44 (m, 3H, Ph H-3,4,5), 7.42 (m, 2H, Ph H-2,6), 7.37 (m, 1H, H-3), 7.27 (m, 1H, H-4), 7.26 (m, 1H, H-5), 5.44 (s, 1H, COCH=C), 2.96 (d, 3J = 5.4 Hz, 3H, N-CH3);13C-NMR (125 MHz): δ 189.2 (C=O), 167.6 (COCH=C), 141.3 (C-1), 134.8 (Ph C-1), 130.8 (C-2), 130.1 (C-3), 129.9 (C-4), 129.7 (Ph C-4), 129.2 (C-6), 128.5 (Ph C-3,5), 127.7 (Ph C-2,6), 126.5 (C-5), 97.3 (COCH=C, 1J = 164.5 Hz, 3J(C,NH) = 3.6 Hz), 31.6 (N-CH3, 1J = 138.5 Hz, 2J(NCH3,NH) = 3.4 Hz, 4J(NCH3,COCH=C) = 1.1 Hz); 15N-NMR (50 MHz): δ −281.5 (N-CH3); IR: 1595 (C=O) cm−1; MS m/z (%): 273/271 (M+, 12/43), 256/254 (22/45), 236 ([M − Cl]+, 100), 160 ([M–C6H4Cl]+, 57), 141/139 ([COC6H4Cl]+, 14/33), 117 ([CH=C(NH)C6H5]+, 66), 113/111 ([C6H4Cl]+, 13/38), 104 ([HNCC6H5]+, 25), 102 ([CH=CC6H5]+, 97), 77 ([C6H5]+, 74). Calcd. for C16H14ClNO: C, 70.72; H, 5.19; N, 5.15. Found: C, 70.32; H, 5.22; N, 5.32.

4.2.8. Preparation of 1-methyl-2-phenylquinolin-4(1H)-one (11)

Potassium carbonate (2 mmol, 277 mg) was added to a solution of 10 (220 µmol, 60 mg) in DMF (5 mL). The resulting mixture was refluxed for 52 h under a N2 atmosphere (N2 balloon). The solvent was then removed under reduced pressure and water (20 mL) was added to the residue. The resulting solution was adjusted to a slightly basic pH with 5% HCl and extracted with CH2Cl2 (2 ° 15 mL). The combined organic layers were washed with a saturated NaHCO3 solution and a saturated NaCl solution and then dried over anhydrous Na2SO4. After removal of the solvent, the oily residue was purified by column chromatography through silica gel (eluent: EtOAc/NEt3, 20:1 v/v.) to generate 11. Yield: 37 mg, 72%; yellowish crystals, mp 137–140 °C (EtOH/H2O) (lit. [53] mp 142–145 °C); 1H-NMR (500 MHz): δ 8.50 (dd, 3J = 8.1 Hz, 4J = 1.7 Hz, 1H, H-5), 7.71 (ddd, 3J(H7,H6) = 7.0 Hz, 3J(H7,H8) = 8.6 Hz, 4J = 1.7 Hz, 1H, H-7), 7.55 (d, 3J = 8.6 Hz, 1H, H-8), 7.50 (m, 3H, Ph H-3,4,5), 7.42 (m, 3J(H6,H7) = 7.0 Hz, 3J(H6,H5) = 8.1 Hz, 4J = 1.0 Hz, 1H, H-6), 7.41 (m, 2H, Ph H-2,6), 6.29 (s, 1H, H-3), 3.60 (s, 3H, N-CH3); 13C-NMR (125 MHz): δ 177.6 (C-4, 2J(C4,H3) = 1.4 Hz, 3J(C4,H5) = 3.9 Hz), 154.7 (C-2, 2J(C2,H3) = 3.7 Hz, 3J(C2,NCH3) = 3.1 Hz), 141.9 (C-8a, 3J(C8a,H5) = 7.6 Hz, 3J(C8a,H7) = 9.5 Hz, 3J(C8a,NCH3) = 2.9 Hz), 135.9 (Ph C-1, 3J(Ph C1,H3) = 3.9 Hz), 132.3 (C-7), 129.6 (Ph C-4), 128.8 (Ph C-3,5), 128.5 (Ph C-2,6), 126.8 (C-4a, 3J(C4a,H3) = 4.8 Hz), 126.7 (C-5, 3J(C5,H7) = 7.8 Hz), 123.6 (C-6), 115.9 (C-8), 112.7 (C-3, 1J(C3,H3) = 165.8 Hz), 37.2 (N-CH3, 1J = 140.1 Hz); 15N-NMR (50 MHz): δ −262.1 (N-1); MS m/z (%): 235 (M+, 100), 207 ([M–C=O]+, 100), 206 ([M–H,–C=O]+, 55), 102 (40), 77 ([C6H5]+, 47).

Acknowledgements

We are grateful to L. Jirovetz and Ing. P. Unteregger for recording the mass spectra.
  • Sample Availability: Samples of the compounds are available from the authors.

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Fuchs, F.C.; Eller, G.A.; Holzer, W. Heterocyclic Analogs of Thioflavones: Synthesis and NMR Spectroscopic Investigations. Molecules 2009, 14, 3814-3832. https://doi.org/10.3390/molecules14093814

AMA Style

Fuchs FC, Eller GA, Holzer W. Heterocyclic Analogs of Thioflavones: Synthesis and NMR Spectroscopic Investigations. Molecules. 2009; 14(9):3814-3832. https://doi.org/10.3390/molecules14093814

Chicago/Turabian Style

Fuchs, Ferdinand C., Gernot A. Eller, and Wolfgang Holzer. 2009. "Heterocyclic Analogs of Thioflavones: Synthesis and NMR Spectroscopic Investigations" Molecules 14, no. 9: 3814-3832. https://doi.org/10.3390/molecules14093814

APA Style

Fuchs, F. C., Eller, G. A., & Holzer, W. (2009). Heterocyclic Analogs of Thioflavones: Synthesis and NMR Spectroscopic Investigations. Molecules, 14(9), 3814-3832. https://doi.org/10.3390/molecules14093814

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