INTRODUCTION

Organic sulfur compounds constitute one of the most important classes of organic compounds which have found wide application in various fields of human activity [1–9]. Among them, of particular interest are sulfonyl-containing compounds (sulfones), including β-halovinyl sulfones and their derivatives obtained by the substitution of halogen by other functional groups [10–16]. Such compounds are used in the synthesis of drugs, in agrochemical industry, and in the manufacture of new materials. Various methods for the synthesis of β-halovinyl sulfones are available from the literature [17–20]; however, the direct addition of sulfonyl halides to internal alkynes provided poor yields [21]. The use of a LED source with an emission maximum of λ 400 nm made it possible to achieve nearly quan­titative yields [22], but in this case 2 equiv of ArSO2I was necessary due to side reactions of intermediate radical species [23].

Taking into account that addition reactions should be atom-economic, i.e., they should proceed with equivalent amounts of the reactants, we tried to reduce the irradiation power by using a light source emitting at a longer wavelength. Herein, we report the iodosul­fonylation of internal alkynes 1a–1g with arenesulfonyl iodides at a molar ratio of 1:1 under irradiation with red light, other conditions being the same as in the iodosulfonylation initiated at λ 400 nm (acetonitrile, 25°C, 1 h) [22]. It turned out that the reactions provided almost equally high yields and selectivity, but in some cases a longer time was required to complete the process.

RESULTS AND DISCUSSION

The iodosulfonylation of internal alkynes 1a–1g (namely diarylacetylene 1a, alkylarylacetylene 1b, dialkylacetylene 1c, functionally substituted phenyl­acetylenes 1d–1f, and hetarylalkyne 1g) with p-tolu­ene­sulfonyl iodide (2, TsI) was carried out in aceto­nitrile at room temperature under LED irradiation with λmax = 625 nm (Scheme 1). All alkynes containing an aryl or hetaryl substituent reacted with TsI to afford exclusively the corresponding (E)-β-iodovinyl sulfones 3a–3g with high yields and selectivity.

Scheme
scheme 1

1.

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We also studied the reaction of diphenylacetylene (4) with 4-haloarenesulfonyl iodides 5a–5c under similar conditions (Scheme 2). As a result, sulfones 6a–6c were obtained in nearly quantitative yields.

Scheme
scheme 2

2.

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EXPERIMENTAL

Initial compounds and solvents were obtained from commercial sources and were used without further purification. Thin-layer chromatography was per­formed on Silica gel 60 F254 plates (Merck); visualiza­tion was done under UV light (λ 254 nm). The products were isolated by flash chromatography on EM Science 60 silica gel (230–400 mesh). The 1H, 13C, and 19F NMR spectra were recorded on a Bruker Avance III HD spectrometer at 400, 101, and 376 MHz, respec­tively, using CDCl3 as solvent; the 1H and 13C chemical shifts were measured relative to the residual proton and carbon signals of the deuterated solvent. LED strips with λmax = 625 nm (Arlight RT 2-5000 12V Red 2x, 14.4 W/m) were used as a radiation source. A piece of LED strip was attached to the inner surface of an alu­minum cup (inner diameter 90 mm, height 79 mm) with ventilation holes (diameter 8 mm) in the lower part (Fig. 1). The photoreactor was powered using an adjustable power supply (12 V, 1.31 A). During the reaction, the photoreactor was blown with air using a fan (105 m3 h–1).

Fig. 1.
figure 1

Photoreactor used for iodosulfonylation of internal alkynes.

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General procedure for the synthesis of β-iodo­vinyl sulfones. A 8-mL vial was charged with a solu­tion of alkyne 1a–1g or 4 (0.5 mmol) in acetonitrile (4 mL), sulfonyl iodide 2 or 5a–5c (0.5 mmol), and argon was bubbled through the mixture over a period of 1 min. The mixture was then stirred at 25°C under irradiation with red light (λ = 625 nm) for 1 h. The solvent was evaporated under reduced pressure, and the residue was purified by flash column chromatog­raphy using methylene chloride–petroleum ether as eluent.

(E)-[1-Iodo-2-(4-methylbenzenesulfonyl)ethene-1,2-diyl]dibenzene (3a). Yield 207 mg (90%), white powder, mp 195–196°C (from (CH2Cl2); published data [24]: mp 188.5–190.2°C. 1H NMR spectrum, δ, ppm: 2.37 s (3H, CH3), 7.11 d (2H, Ts, J = 8.2 Hz), 7.15–7.22 m (2H, Ph), 7.27 d (2H, Ts, J = 8.2 Hz), 7.31–7.46 m (8H, Ph). 13C NMR spectrum, δC, ppm: 21.7, 118.2, 127.5, 128.0, 128.5, 128.7, 129.1, 129.3, 130.4, 136.9, 139.5, 142.7, 144.4, 149.3. The NMR spectra were in agreement with those reported in [19].

(E)-1-(1-Iodo-1-phenylbut-1-ene-2-sulfonyl)-4-methylbenzene (3b). Yield 204 mg (99%), white powder, mp 130–132°C (from CH2Cl2); published data [22]: mp 128–130°C. 1H NMR spectrum, δ, ppm: 1.32 t (3H, CH2CH3, J = 7.4 Hz), 2.37 s (3H, C6H4CH3), 2.96 q (2H, CH2CH3, J = 7.4 Hz), 7.01 d.d (2H, J = 7.5, 2.0 Hz), 7.08 d (2H, J = 8.0 Hz), 7.23–7.12 m (3H), 7.27 d (2H, J = 7.0 Hz). 13C NMR spectrum, δC, ppm: 12.9, 21.7, 33.6, 77.2, 115.0, 127.7, 127.8, 127.9, 128.6, 129.4, 130.5, 137.9, 142.9, 143.9, 149.9. The NMR spectra were in agreement with those reported in [22].

(E)-1-(4-Iodohex-3-ene-3-sulfonyl)-4-methylben­zene (3c). Yield 124 mg (68%), white powder, mp 80–82°C (from CH2Cl2); published data [22]: mp 80–82°C. 1H NMR spectrum, δ, ppm: 1.05 t (3H, CH3, J = 7.2 Hz), 1.11 t (3H, CH3, J = 7.4 Hz), 2.44 s (3H, C6H4CH3), 2.66 q (2H, CH2, J = 7.4 Hz), 3.21 q (2H, CH2, J = 7.2 Hz), 7.35 d (2H, J = 8.1 Hz), 7.75 d (2H, J = 8.1 Hz). 13C NMR spectrum, δC, ppm: 12.8, 14.9, 21.8, 34.2, 37.6, 127.4, 129.1, 130.0, 138.6, 144.6, 145.2. The NMR spectra were in agreement with those reported in [22].

(E)-3-Iodo-1-(4-methoxyphenyl)-2-(4-methylben­zene­sulfonyl)-3-phenylprop-2-en-1-ol (3d). Yield 205 mg (79%), white powder, mp 162–163°C (from CH2Cl2); published data [22]: mp 161–163°C. 1H NMR spectrum, δ, ppm: 2.33 s (3H, C6H4CH3), 3.86 s (3H, OCH3), 6.31 s (1H), 6.85–7.25 m (11H), 7.52–7.62 m (2H). 13C NMR spectrum, δC, ppm: 21.7, 55.5, 83.2, 114.2, 119.2, 126.8, 127.6, 127.7, 129.0, 129.1, 132.1, 138.0, 141.9, 144.1. The NMR spectra were in agreement with those reported in [22].

(E)-3-Iodo-1-(4-methoxyphenyl)-2-(4-methylben­zenesulfonyl)-3-phenylprop-2-en-1-one (3e). Yield 246 mg (95%), white powder, mp 184–185°C (from CH2Cl2); published data [22]: mp 183–185°C. 1H NMR spectrum, δ, ppm: 2.38 s (3H, C6H4CH3), 3.93 s (3H, OCH3), 7.02–7.09 m (2H), 7.09–7.14 m (2H), 7.14–7.20 m (2H), 7.22–7.31 m (4H), 7.32– 7.38 m (2H), 8.15–8.25 m (2H). 13C NMR spectrum, δC, ppm: 21.8, 55.8, 113.5, 114.7, 127.1, 127.6, 128.0, 128.6, 129.5, 129.6, 132.9, 137.6, 140.4, 144.9, 149.7, 165.0, 189.3. The NMR spectra were in agreement with those reported in [22].

(E)-1-Iodo-5-methyl-2-(4-methylbenzene­sul­fonyl)-1-phenylhex-1-en-3-ol (3f). Yield 202 mg (86%), white powder, mp 149–150°C (from CH2Cl2); published data [22]: mp 148–150°C. 1H NMR spec­trum, δ, ppm: 1.10 m (6H, CH3), 1.93–1.78 m (1H, CH2), 2.16–1.99 m (1H, CHCH3), 2.26 m (1H, CH2), 2.34 s (3H, C6H4CH3), 3.54 s (1H), 5.10 d.d (1H, J = 10.3, 4.0 Hz), 6.63 s (1H), 7.22–6.79 m (8H). 13C NMR spectrum, δC, ppm: 21.7, 21.9, 23.9, 25.1, 45.2, 81.7, 116.1, 127.3, 127.6, 128.8, 129.2, 138.3, 141.9, 143.9, 150.1. The NMR spectra were in agreement with those reported in [22].

(E)-3-(1-Iodo-2-(4-methylbenzenesulfonyl)oct-1-en-1-yl)thiophene (3g). Yield 206 mg (87%), white powder, mp 102–104°C (from CH2Cl2); published data [22]: mp 103–104°C. 1H NMR spectrum, δ, ppm: 0.89–1.03 m (3H, CH2CH3), 1.25–1.57 m (6H, CH2), 1.70–1.90 m (2H), 2.37 s (3H, C6H4CH3), 2.86–3.03 m (2H, CH2), 6.52 d (1H, J = 5.0 Hz), 6.92–7.04 m (1H), 7.10 d (2H, J = 8.0 Hz), 7.24–7.29 m (3H). 13C NMR spectrum, δC, ppm: 14.2, 21.7, 22.7, 28.4, 29.4, 31.6, 39.7, 108.6, 124.7, 126.1, 127.3, 128.1, 129.3, 138.1, 141.8, 143.6, 150.8. The NMR spectra were in agree­ment with those reported in [22].

(E)-[1-(4-Fluorobenzenesulfonyl)-2-iodoethene-1,2-diyl]dibenzene (6a). Yield 215 mg (93%), white powder, mp 202–203°C (from CH2Cl2); published data [25]: mp 205–206°C. 1H NMR spectrum, δ, ppm: 6.97 t (2H, J = 8.4 Hz), 7.14–7.25 m (2H), 7.30–7.48 m (10H). 13C NMR spectrum, δC, ppm: 115.98 d (J = 22.6 Hz), 118.5, 127.5, 128.1, 128.6, 129.3, 129.5, 130.4, 131.37 d (J = 9.6 Hz), 135.90 d (J = 3.0 Hz), 139.2, 142.4, 148.9, 165.54 d (J = 256.0 Hz). 19F NMR spectrum: δF –103.5 ppm. The NMR spectra were in agreement with those reported in [25].

(E)-[1-(4-Chlorobenzenesulfonyl)-2-iodoethene-1,2-diyl]dibenzene (6b). Yield 223 mg (93%), white powder, mp 196–198°C (from CH2Cl2); published data [25]: mp 197–199°C. 1H NMR spectrum, δ, ppm: 7.06–7.13 m (2H), 7.14–7.22 m (4H), 7.22–7.34 m (8H). 13C NMR spectrum, δC, ppm: 118.9, 127.5, 128.1, 128.7, 129.0, 129.3, 129.6, 130.0, 130.4, 131.7, 138.4, 139.0, 140.1, 142.4, 148.8. The NMR spectra were in agreement with those reported in [25].

(E)-[1-(4-Bromobenzenesulfonyl)-2-iodoethene-1,2-diyl]dibenzene (6c). Yield 249 mg (95%), white powder, mp 210–211°C (from CH2Cl2); published data [22]: mp 210–211°C. 1H NMR spectrum, δ, ppm: 7.16–7.29 m (4H), 7.30–7.49 m (10H). 13C NMR spec­trum, δC, ppm: 118.9, 127.5, 128.1, 128.7, 128.7, 129.4, 129.6, 130.0, 130.4, 132.0, 139.0, 139.0, 142.4, 148.8. The NMR spectra were in agreement with those reported in [25].

CONCLUSIONS

Thus, an increase of the radiation wavelength in the iodosulfonylation of internal alkynes makes it possible to conduct the reaction using stoichiometric amounts of the reactants. The absence of byproducts facilitates the isolation and purification of the target β-iodovinyl sulfones.