Mediated Decarboxylative Trifluoromethylthiolation of α,β-Unsaturated

‡School of Biological and Medical Engineering, Hefei University of Technology, Hefei 230009, P. R. China. §Anhui Provincial Laboratory of Heterocyc...
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Cu(II)-Mediated Decarboxylative Trifluoromethylthiolation of α,βUnsaturated Carboxylic Acids Zhi-Fei Cheng,†,∥ Ting-Ting Tao,†,∥ Yi-Si Feng,*,†,§ Wei-Ke Tang,† Jun Xu,‡ Jian-Jun Dai,‡ and Hua-Jian Xu*,†,‡ †

Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009, P. R. China ‡ School of Biological and Medical Engineering, Hefei University of Technology, Hefei 230009, P. R. China § Anhui Provincial Laboratory of Heterocyclic Chemistry, Maanshan 243110, P. R. China S Supporting Information *

ABSTRACT: A tunable method for the direct trifluoromethylthiolation of α,β-unsaturated carboxylic acids was developed to afford trifluoromethylthiolated ketones or alkenes. The reaction proceeds smoothly under mild conditions and shows an excellent functional group tolerance.

Scheme 1. Methods for the Syntheses of α-SCF3-Substituted Ketones

T

he trifluoromethylthio (F3CS) group exhibits unique properties, such as high lipophilicity, and it has a strong electron-withdrawing effect. This moiety is therefore an important functional group, which is employed in the fields of biomedicine and agrochemistry.1 In recent years, the development of efficient methods for the incorporation of the trifluoromethylthio group into organic molecules has attracted increasing attention. Research in this area has been reported by Shen,2 Qing,3 Hu,4 and others.5 The α-SCF3-substituted ketones are important structural elements in materials science and chemical biology. The biological activities of many medicine molecules can be changed through the α-SCF3substituted ketone groups that they contain (Figure 1). Various

recent work of Qing et al.10 Herein, we report on the trifluoromethylthiolation of α,β-unsaturated carboxylic acids to afford trifluoromethylthiolated ketones (Scheme 1b). This reaction system is also applicable to cinnamic acids, affording trifluoromethylthiolated alkenes. We commenced with the optimization of the reaction conditions by selecting 3-phenylpropiolic acid (1a) and AgSCF3 as model substrates (Table 1). With Cu(OAc)2 (2 equiv) as the mediator and K2S2O8 (3 equiv) as the oxidant, it was found that the use of CH3CN as the solvent afforded the desired product 2a in 7% yield at 80 °C under an argon atmosphere (entry 1). Next, other solvents such as DCE, toluene/H2O (v/v = 1:1), and CH3CN/H2O (v/v = 1:1) were examined (entries 2−4). It was found that toluene/H2O was the optimal medium for the transformation; the yield increased to 39%. The use of other copper salts was then also considered,

Figure 1. Bioactive compounds containing α-SCF3-substituted ketones.

efficient synthetic methods have been reported, such as the trifluoromethylthiolation of α-haloketones,6 β-ketoesters,7 silyl enol ethers,8 simple ketones,9 and cinnamic acids10 with different SCF3 sources (Scheme 1a). Although many significant contributions have been achieved in this field, the decarboxylative trifluoromethylthiolation of propiolic acids to afford trifluoromethylthiolated ketones has not been reported yet. Decarboxylative coupling reactions are important methods for the construction of chemical bonds and have attracted great attention. We are specifically interested in the use of decarboxylation reactions to synthesize trifluoromethylthiolated ketones of α,βunsaturated carboxylic acids. This study was inspired by the © 2017 American Chemical Society

Received: October 17, 2017 Published: December 7, 2017 499

DOI: 10.1021/acs.joc.7b02232 J. Org. Chem. 2018, 83, 499−504

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The Journal of Organic Chemistry Table 1. Optimization of the Reaction Conditionsa

Cu salt

oxidant (equiv)

1 2 3

Cu(OAc)2 Cu(OAc)2 Cu(OAc)2

K2S2O8 (3) K2S2O8 (3) K2S2O8 (3)

4

Cu(OAc)2

K2S2O8 (3)

5 6 7 8 9 10 11 12

CuI Cu CuCl2 CuSO4·5H2O

K2S2O8 K2S2O8 K2S2O8 K2S2O8 K2S2O8

13 14 15 16 17

CuSO4·5H2O CuSO4·5H2O CuSO4·5H2O CuSO4·5H2O CuSO4·5H2O

Na2S2O8 (3) (NH4)2S2O8 (3) Na2S2O8 (2) Na2S2O8 (4) Na2S2O8 (3) Na2S2O8 (3) Na2S2O8 (3)

18

CuSO4·5H2O

Na2S2O8 (3)

19

CuSO4·5H2O

Na2S2O8 (3)

20c

CuSO4·5H2O

Na2S2O8 (3)

entry

CuSO4·5H2O CuSO4·5H2O CuSO4·5H2O

(3) (3) (3) (3) (3)

Scheme 2. Scope of Propiolic Acids for Preparation of αSCF3-Substituted Ketonesa,b

temp (°C)

yield (%)b

CH3CN DCE toluene/H2O (1:1) CH3CN/H2O (1:1) toluene/H2O toluene/H2O toluene/H2O toluene/H2O toluene/H2O toluene/H2O toluene/H2O toluene/H2O

80 80 80

7 39

80

20

80 80 80 80 80 80 80 80

35 16 36 54

toluene/H2O toluene/H2O toluene/H2O toluene/H2O toluene/H2O (1:2) toluene/H2O (2:1) toluene/H2O (3:1) toluene/H2O

80 80 70 90 80

61 67 57 63 60

80

58

80

53

80

18

solvent

a

Reaction conditions: 1 (0.2 mmol), AgSCF3 (0.4 mmol, 2 equiv), CuSO4·5H2O (0.4 mmol, 2 equiv), Na2S2O8 (0.6 mmol, 3 equiv), and toluene/H2O (v/v = 1:1, 2 mL) at 80 °C for 8 h under an argon atmosphere. bIsolated yields based on 1.

69 55

with a strong electron-donating substituent such as paramethoxy propiolic acid was used in this reaction system, the acetenyl trifluoromethyl thioether (2i) was obtained. Unfortunately, alkylpropiolic acid was not suitable this reaction system. Once we had identified that the cinnamic acids were suitable substrates for this reaction system, we aimed to further expand the substrate scope to α,β-unsaturated carboxylic acids (Scheme 3). Pleasingly, various vinyl trifluoromethyl thioethers could be conveniently synthesized through decarboxylative trifluoromethylthiolation of cinnamic acids with AgSCF3 under the typical reaction conditions established (AgSCF3 (0.4 mmol, 2 equiv), CuSO4·5H2O (0.4 mmol, 2 equiv), Na2S2O8 (0.6 mmol, 3 equiv), and toluene/H2O (v/v = 1:1, 2 mL) at 60 °C for 8 h under an air atmosphere). It was found that various cinnamic acids could smoothly undergo decarboxylative trifluoromethylthiolation to generate the desired vinyl trifluoromethyl thioether products in modest yields. Electron-donating substituents such as Me (4a, 4h, 4j), OMe (4b, 4i, and 4k), OEt (4c), OBn (4d), and OAc (4e) were well-tolerated in the current reaction system. In most cases, the E/Z selectivity was good. Furthermore, the halide groups such as F (4f) and Cl (4g) were also suitable for use in the reaction, possibly enabling further functionalization at these positions. The cinnamic acids bearing ortho- and meta-substituents worked well to afford the corresponding vinyl trifluoromethyl thioether products in 55− 62% yields (4h−4k). The reactions of disubstituted and trisubstituted cinnamic acids afforded the desired products in 50−60% yields under the above conditions (4l−4n). When cinnamic acid was employed in the transformation, the corresponding product was obtained in 73% yield. Furthermore, the reaction could also tolerate sterically hindered cinnamic acids, giving the desired products in 63% and 62% yields (4p and 4q). The 9-fluorenyl-substituted acrylic acid gave a 49% yield of the product (4r). A scale-up experiment was successfully carried out (0.324 g, 2 mmol) under the optimal conditions (Scheme 4), and it afforded 4a with a relatively high yield of 54%. To elucidate a plausible reaction mechanism, the following experiment was carried out (Scheme 5). Under the optimal conditions, when the radical-trapping reagent TEMPO (2,2,6,6tetramethyl-1-oxylpiperidine) was added, the reaction was

a

Reaction conditions: 1a (0.2 mmol), AgSCF3 (0.4 mmol, 2 equiv), oxidant (0.6 mmol, 3 equiv), and copper mediator (2 equiv) in 2 mL of solvent for 8 h under an argon atmosphere. bIsolated yields based on 1a. cCuSO4·5H2O (10 mol %) was used.

CuI, Cu, CuCl2, and CuSO4·5H2O. To our delight, we found that CuSO4·5H2O was the optimal mediator; an increased yield of 54% was achieved (entry 8). Results of the control experiment proved that CuSO4·5H2O and K2S2O8 were essential (entries 9 and 10). Furthermore, the use of Na2S2O8 and (NH4)2S2O8 as oxidants was also considered. When Na2S2O8 was employed, the yield of 2a was improved to 69% (entry 11). Finally, changing the quantity of Na2S2O8 and the reaction temperature also led to similar yields of 2a (55−67%, entries 12−16). Furthermore, we changed the ratio of the mixed solvents, and that also led to similar yields of the desired product (53−60%, entries 17−19). When the amount of CuSO4·5H2O could be reduced to 10 mol %, the yield of the product decreased obviously (entry 20). With the optimized reaction conditions in hand, we explored the scope of propiolic acids for the preparation of α-SCF3substituted ketones. As summarized in Scheme 2, all substrates examined here bearing both electron-withdrawing and electrondonating groups in the aromatic rings afforded the desired products in moderate to good yields (42−69%). Pleasingly, propiolic acids with strong electron-withdrawing substituents were also suitable substrates; they afforded the corresponding α-SCF3-substituted ketones in 42−53% yields (2e−2g). The reactions of disubstituted propiolic acids afforded the desired product in 58% yield (2h). Surprisingly, when propiolic acid 500

DOI: 10.1021/acs.joc.7b02232 J. Org. Chem. 2018, 83, 499−504

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The Journal of Organic Chemistry

2a (18O-2a) was 100%, clearly indicating that the oxygen atom of the carbonyl group in 2a was from the water (Scheme 6).

Scheme 3. Scope of Cinnamic Acids for Preparation of Vinyl Trifluoromethyl Thioestersa,b

Scheme 6. Isotope-Labeling Experiment

On the basis of the above experimental results and previous reports,3c,10,11 we propose a plausible mechanism as shown in Scheme 7. Initially, the oxidation of AgSCF3 by Na2S2O8 affords Scheme 7. Proposed Reaction Mechanism

a

Reaction conditions: 3 (0.2 mmol), AgSCF3 (0.4 mmol, 2 equiv), CuSO4·5H2O (0.4 mmol, 2 equiv), Na2S2O8 (0.6 mmol, 3 equiv), and toluene/H2O (v/v = 1:1, 2 mL) at 60 °C for 8 h under an air atmosphere. bIsolated yields based on 3. The E/Z ratio was determined by 19F NMR spectroscopy. cUnder 80 °C.

the Ag(II)SCF3 species, which then triggers the F3CS radical B after the following transfer of a single electron course. Meanwhile, Cu(II) carboxylates A1 and A2 are generated from the incorporation of α,β-unsaturated carboxylic acid and copper sulfate. Addition of the F3CS radical at the α-position of the double bond in cupric cinnamate would give radicals C1 and C2, and the reaction then proceeds via the elimination of carbon dioxide and Cu(I) to generate the products of trifluoromethylthiolated alkenes or ketones. In summary, we report a convenient copper(II)-mediated decarboxylative trifluoromethylthiolation reaction of α,βunsaturated carboxylic acids with AgSCF3. This method provides a useful and practical strategy for the synthesis of trifluoromethylthiolated ketones or alkenes. The reaction can tolerate many important functional groups, and it provides a new pathway for the construction of C−SCF3 bonds. A preliminary mechanistic investigation suggests the involvement of a radical species. The oxygen atom of the carbonyl of product 2 was derived from water.

Scheme 4. Scale-Up Experiment

Scheme 5. Radical-Trapping Experiment

■

completely suppressed; no product was detected, and the TEMPO-trifluoromethylthio adduct was detected by GC−MS. (See the Supporting Information.) This result suggested that the reaction may proceed via a radical pathway. Molecular oxygen is essential for the formation of α-SCF3substituted ketones. An isotope-labeling experiment was performed using 18O-labeled water as a cosolvent instead of regular water. The content of the obtained 18O-labeled product

EXPERIMENTAL SECTION

General Information and Materials. All of the reactions were conducted in oven-dried Schlenk tubes. All solvents were obtained from commercial suppliers and used without further purification. Flash column chromatographic purification of products was accomplished using forced-flow chromatography on silica gel (200−300 mesh). 1H NMR and 13C NMR spectra were recorded on a 600 MHz 501

DOI: 10.1021/acs.joc.7b02232 J. Org. Chem. 2018, 83, 499−504

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The Journal of Organic Chemistry spectrometer in CDCl3 and (CD3)2SO. Data for 1H NMR are reported as follows: chemical shift (ppm, scale), multiplicity, coupling constant (Hz), and integration. Data for 13C NMR are reported in terms of the chemical shift (ppm, scale), multiplicity, and coupling constant (Hz). Gas chromatographic (GC) analyses were performed on a GC equipped with a flame ionization detector and an Rtx@-65 (30 m × 0.32 mm ID × 0.25 μm df) column. Copper-Mediated Decarboxylative Trifluoromethylthiolation of Propiolic Acids with AgSCF3. A sealed 25 mL Schlenk tube with a magnetic stir bar was charged with propiolic acids (0.2 mmol), AgSCF3 (0.4 mmol, 2.0 equiv), CuSO4·5H2O (0.4 mmol, 2 equiv), Na2S2O8 (0.6 mmol, 3 equiv), and toluene/H2O (v/v = 1:1, 2 mL), and the reaction mixture was heated at 80 °C under an argon atmosphere for 8 h. The reaction mixture was then allowed to cool to room temperature, diluted with ethyl acetate, and washed with water, and then the organic layer was dried over Mg2SO4. After being concentrated in vacuo, the crude product was purified by column chromatography on silica gel (ethyl acetate/petroleum ether). Copper-Mediated Decarboxylative Trifluoromethylthiolation of Cinnamic Acids with AgSCF3. A sealed 25 mL Schlenk tube with a magnetic stir bar was charged with cinnamic acids (0.2 mmol), AgSCF3 (0.4 mmol, 2.0 equiv), CuSO4·5H2O (0.4 mmol, 2 equiv), Na2S2O8 (0.6 mmol, 3 equiv), and toluene/H2O (v/v = 1:1, 2 mL), and the reaction mixture was heated at 60 °C under an air atmosphere for 8 h. The reaction mixture was then allowed to cool to room temperature, diluted with ethyl acetate, and washed with water, and then the organic layer was dried over Mg2SO4. After being concentrated in vacuo, the crude product was purified by column chromatography on silica gel (ethyl acetate/petroleum ether). Spectral Data of All Products. 1-Phenyl-2-((trifluoromethyl)thio)ethanone (2a).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 69% yield as a yellow oil (30.4 mg): 1H NMR (600 MHz, CDCl3) δ 7.95 (d, J = 8.1 Hz, 2H), 7.64 (t, J = 7.3 Hz, 1H), 7.51 (t, J = 7.1 Hz, 2H), 4.52 (s, 2H); 13C NMR (151 MHz, CDCl3) δ 192.0 (s), 134.7 (s), 134.2 (s), 131.7 (q, J = 306.4 Hz), 129.0 (s), 128.4 (s), 38.4 (q, J = 1.8 Hz); 19F NMR (564 MHz, CDCl3) δ −41.46 (s). 1-(p-Tolyl)-2-((trifluoromethyl)thio)ethanone (2b).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 63% yield as a yellow oil (29.5 mg): 1H NMR (600 MHz, CDCl3) δ 7.85 (d, J = 8.0 Hz, 2H), 7.30 (d, J = 8.0 Hz, 2H), 4.50 (s, 2H), 2.44 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 191.6 (s), 145.4 (s), 132.2 (s), 130.8 (q, J = 306.3 Hz), 129.7 (s), 128.5 (s), 38.4 (q, J = 1.8 Hz), 21.8 (s); 19F NMR (564 MHz, CDCl3) δ −41.46 (s). 1-(4-Chlorophenyl)-2-((trifluoromethyl)thio)ethanone (2c).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 50% yield as a yellow oil (25.4 mg): 1H NMR (600 MHz, CDCl3) δ 7.89 (d, J = 8.6 Hz, 2H), 7.48 (d, J = 8.6 Hz, 2H), 4.47 (s, 2H); 13C NMR (151 MHz, CDCl3) δ 190.9 (s), 140.9 (s), 132.9 (s), 130.5 (q, J = 306.6 Hz), 129.7 (s), 129.5 (s), 38.1 (q, J = 1.7 Hz); 19F NMR (564 MHz, CDCl3) δ −41.44 (s). 1-(4-Bromophenyl)-2-((trifluoromethyl)thio)ethanone (2d).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 55% yield as a yellow oil (32.8 mg): 1H NMR (600 MHz, CDCl3) δ 7.82 (d, J = 8.5 Hz, 2H), 7.66 (d, J = 8.5 Hz, 2H), 4.46 (s, 2H); 13C NMR (151 MHz, CDCl3) δ 191.1 (s), 133.3 (s), 132.3 (s), 130.5 (q, J = 306.0 Hz), 129.9 (s), 129.5 (s), 38.1 (q, J = 1.9 Hz); 19F NMR (564 MHz, CDCl3) δ −41.43 (s). 1-(4-Nitrophenyl)-2-((trifluoromethyl)thio)ethanone (2e).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:15) and obtained in 53% yield as a yellow oil (28.1 mg): 1H NMR (600 MHz, CDCl3) δ 8.37 (d, J = 8.8 Hz, 2H), 8.13 (d, J = 8.9 Hz, 2H), 4.51 (s, 2H); 13C NMR (151 MHz, CDCl3) δ 190.7 (s), 150.9 (s), 139.0 (s), 130.3 (q, J = 306.9 Hz), 129.5 (s), 124.2 (s), 38.2 (q, J = 2.0 Hz); 19F NMR (564 MHz, CDCl3) δ −41.37 (s).

Ethyl 4-(2-((Trifluoromethyl)thio)acetyl)benzoate (2f). By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:15) and obtained in 42% yield as a yellow oil (24.5 mg): 1H NMR (600 MHz, CDCl3) δ 8.17 (d, J = 8.1 Hz, 2H), 8.01 (d, J = 8.1 Hz, 2H), 4.53 (s, 2H), 4.43 (q, J = 7.1 Hz, 2H), 1.43 (t, J = 7.1 Hz, 3H); 13C NMR (151 MHz, CDCl3) δ 191.6 (s), 165.4(s), 137.7 (s), 135.3 (s), 130.7 (q, J = 306.6 Hz), 130.1 (s), 128.3 (s), 61.7 (s), 38.4 (q, J = 2.0 Hz); 19F NMR (564 MHz, CDCl3) δ −41.41 (s); HRMS calcd for C12H11F3O3NaS [M + Na]+ 315.0279, found 315.0269; MS (EI) m/z (%) 63.07 (15.53), 69.04 (13.61), 77.08 (24.54), 78.10 (17.49), 89.10 (18.72), 107.11 (48.46), 122.09 (25.88), 133.10 (49.05), 151.13 (100.00), 220.13 (54.58), 292.15 (53.19). 3-(2-((Trifluoromethyl)thio)acetyl)benzonitrile (2g).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:15) and obtained in 48% yield as a yellow oil (23.5 mg): 1H NMR (600 MHz, CDCl3) δ 8.24 (s, 1H), 8.18 (d, J = 7.9 Hz, 1H), 7.92 (d, J = 7.7 Hz, 1H), 7.68 (t, J = 7.8 Hz, 1H), 4.48 (s, 2H); 13C NMR (151 MHz, CDCl3) δ 190.3 (s), 137.0 (s), 135.4 (s), 132.3 (s), 132.0 (s), 130.3 (q, J = 306.8 Hz), 130.1 (s), 117.4 (s), 113.7 (s), 37.9 (q, J = 1.8 Hz); 19F NMR (564 MHz, CDCl3) δ −41.38 (s). 1-(3,4-Dimethylphenyl)-2-((trifluoromethyl)thio)ethanone (2h). By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 58% yield as a yellow oil (28.8 mg): 1H NMR (600 MHz, CDCl3) δ 7.65 (s, 1H), 7.61 (d, J = 8.0 Hz, 1H), 7.17 (s, 1H), 4.43 (s, 2H), 2.27 (d, J = 1.8 Hz, 6H); 13C NMR (151 MHz, CDCl3) δ 191.8 (s), 144.1 (s), 137.5 (s), 132.6 (s), 132.3 (q, J = 306.7 Hz), 130.1 (s), 129.5 (s), 126.1 (s), 38.4 (q, J = 1.7 Hz), 20.2 (s), 19.8 (s); 19F NMR (564 MHz, CDCl3) δ −41.44 (s); HRMS calcd for C11H11F3ONaS [M + Na]+ 271.0480, found 271.0370; MS (EI) m/ z (%) 65.11 (16.02), 76.13 (16.13), 104.13 (17.11), 121.14 (16.42), 149.16 (37.72), 177.21 (100.00), 178.21 (11.19), 248.23 (8.35). ((4-Methoxyphenyl)ethynyl)(trifluoromethyl)sulfane (2i).3a By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 51% yield as a yellow oil (23.7 mg): 1H NMR (600 MHz, CDCl3) δ 7.46 (d, J = 8.9 Hz, 2H), 6.87 (d, J = 8.8 Hz, 2H), 3.83 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 160.9 (s), 134.4 (s), 128.2 (d, J = 313.4 Hz), 114.1 (s), 113.5 (s), 101.5 (s), 65.1 (q, J = 4.5 Hz), 55.4 (s); 19F NMR (564 MHz, CDCl3) δ −44.07 (s). (4-Methylstyryl)(trifluoromethyl)sulfane (4a).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 72% yield as a yellow oil (30.9 mg) with an E/Z ratio of 95:5: 1H NMR (600 MHz, CDCl3) δ 7.31 (d, J = 7.9 Hz, 2H), 7.18 (d, J = 7.7 Hz, 2H), 7.00 (d, J = 15.3 Hz, 1H), 6.68 (d, J = 15.3 Hz, 1H), 2.37 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 141.7 (q, J = 1.3 Hz), 139.4 (s), 132.3 (s), 130.7(s), 129.5 (q, J = 307.9 Hz), 129.2 (s), 126.8 (s), 110.2 (q, J = 3.0 Hz), 77.2 (s), 77.0 (s), 76.8 (s), 21.3 (s); 19F NMR (564 MHz, CDCl3) δ −42.93 (s). (4-Methoxystyryl)(trifluoromethyl)sulfane (4b).5h By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 66% yield as a yellow oil (30.8 mg) with an E/Z ratio of 96:4: 1H NMR (600 MHz, CDCl3) δ 7.35 (d, J = 8.6 Hz, 2H), 6.89 (d, J = 8.7 Hz, 2H), 6.57 (d, J = 15.2 Hz, 1H), 3.83 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 160.5 (s), 142.1 (q, J = 1.1 Hz), 129.6 (q, J = 307.9 Hz), 128.3 (s), 127.9 (s), 114.2 (s), 108.4 (q, J = 3.0 Hz), 55.3 (s); 19F NMR (564 MHz, CDCl3) δ −43.15 (s). (4-Ethoxystyryl)(trifluoromethyl)sulfane (4c).5i By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 70% yield as a yellow oil (34.7 mg) with an E/Z ratio of 96:4: 1H NMR (600 MHz, (CD3)2SO) δ 7.51 (d, J = 8.4 Hz, 2H), 7.14 (d, J = 15.2 Hz, 1H), 6.89 (d, J = 8.5 Hz, 2H), 6.85 (d, J = 15.2 Hz, 1H), 4.01 (q, J = 6.9 Hz, 2H), 1.29 (t, J = 7.0 Hz, 3H); 13C NMR (151 MHz, (CD3)2SO) δ 159.6 (s), 143.6 (s), 130.8 (s), 130.2 (q, J = 502

DOI: 10.1021/acs.joc.7b02232 J. Org. Chem. 2018, 83, 499−504

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The Journal of Organic Chemistry

(3-Methoxystyryl)(trifluoromethyl)sulfane (4k).5i By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 55% yield as a yellow oil (25.2 mg) with an E/Z ratio of 96:4: 1H NMR (600 MHz, CDCl3) δ 7.27 (dd, J = 13.2, 5.1 Hz, 1H), 6.98 (t, J = 9.3 Hz, 1H), 6.92 (t, J = 17.6 Hz, 2H), 6.87 (t, J = 9.7 Hz, 1H), 6.73 (d, J = 15.3 Hz, 1H), 3.83 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 159.9 (s), 140.8 (s), 136.4 (s), 130.6 (s), 129.9 (s), 129.6 (q, J = 306.1 Hz), 119.4 (s), 114.8 (s), 112.2 (q, J = 3.7 Hz), 55.3 (s); 19F NMR (564 MHz, CDCl3) δ −42.73 (s). 2-Methoxy-4-(2-((trifluoromethyl)thio)vinyl)phenyl Acetate (4l). By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:15) and obtained in 58% yield as a yellow oil (33.8 mg) with an E/Z ratio of 97:3: 1H NMR (600 MHz, (CD3)2SO) δ 7.40 (d, J = 1.6 Hz, 1H), 7.15 (d, J = 5.3 Hz, 2H), 7.13 (dd, J = 8.2, 1.7 Hz, 1H), 7.07 (d, J = 8.1 Hz, 1H), 3.80 (s, 3H), 2.26−2.20 (m, 3H); 13C NMR (151 MHz, (CD3)2SO) δ 168.4 (s), 141.6 (s), 133.7 (s), 131.4 (s), 131.0 (s), 129.6 (q, J = 306.1 Hz), 125.0 (s), 123.1 (s), 120.3 (s), 111.1 (q, J = 3.5 Hz), 56.0 (s), 20.4 (s); 19F NMR (564 MHz, (CD3)2SO) δ −36.95 (s); HRMS calcd for C12H11F3O3NaS [M + Na]+ 315.0279, found 315.0270; MS (EI) m/z (%) 65.08 (11.17), 77.08 (11.80), 109.07 (13.67), 121.08 (34.30), 137.08 (13.70), 149.07 (100.00), 181.14 (20.06), 250.17 (43.31), 251.17 (5.04), 292.36 (46.33). (3,4-Dimethoxystyryl)(trifluoromethyl)sulfane (4m). By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 60% yield as a yellow oil (31.6 mg) with an E/Z ratio of 96:4: 1H NMR (600 MHz, CDCl3) δ 7.00−6.94 (m, 2H), 6.92 (d, J = 7.4 Hz, 1H), 6.85 (t, J = 6.3 Hz, 1H), 6.57 (d, J = 15.2 Hz, 1H), 3.91 (d, J = 9.5 Hz, 6H); 13C NMR (151 MHz, CDCl3) δ 150.2 (s), 149.2 (s), 142.3 (s), 129.9 (q, J = 306.6 Hz), 128.1 (s), 120.7 (s), 111.1 (s), 109.0 (s), 108.7 (q, J = 3.1 Hz), 55.9, 55.8; 19F NMR (564 MHz, CDCl3) δ −43.07 (s); HRMS calcd for C11H12F3O2S [M + H]+ 265.0510, found 265.0503; MS (EI) m/z (%) 51.05 (27.14), 65.05 (40.68), 79.04 (19.73), 109.05 (58.93), 121.06 (49.71), 137.06 (77.14), 151.10 (20.53), 164.09 (100.00), 180.08 (65.44), 195.12 (52.22), 264.14 (47.02). (Trifluoromethyl)(3,4,5-trimethoxystyryl)sulfane (4n).5i By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 50% yield as a yellow oil (29.4 mg) with an E/Z ratio of 98:2: 1H NMR (600 MHz, CDCl3) δ 6.94 (d, J = 15.2 Hz, 1H), 6.65 (d, J = 17.3 Hz, 1H), 6.61 (s, 2H), 3.88 (d, J = 6.0 Hz, 6H), 3.86 (d, J = 6.0 Hz, 3H); 13C NMR (151 MHz, CDCl3) δ 153.5 (s), 141.6 (q, J = 1.7 Hz), 139.2, 130.6 (s), 129.6 (q, J = 306.3 Hz), 110.7 (q, J = 3.6 Hz), 104.0 (s), 61.0 (s), 56.2(s); 19F NMR (564 MHz, CDCl3) δ −42.82 (s). Styryl(trifluoromethyl)sulfane (4o).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 73% yield as a yellow solid (29.7 mg) with an E/Z ratio of 95:5: 1H NMR (600 MHz, CDCl3) δ 7.36 (ddd, J = 20.7, 15.5, 7.1 Hz, 5H), 7.01 (d, J = 15.3 Hz, 1H), 6.74 (d, J = 15.3 Hz, 1H); 13C NMR (151 MHz, CDCl3) δ 141.1 (s), 135.1 (s), 129.6 (q, J = 307.9 Hz), 129.2 (s), 128.8 (s), 126.8 (s), 111.7 (q, J = 3.1 Hz); 19F NMR (564 MHz, CDCl3) δ −42.78 (s). 5-(2-((Trifluoromethyl)thio)vinyl)benzodioxole (4p).5i By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 63% yield as a yellow oil (31.2 mg) with an E/Z ratio of 97:3: 1H NMR (600 MHz, CDCl3) δ 6.93 (t, J = 7.6 Hz, 2H), 6.85 (d, J = 8.0 Hz, 1H), 6.79 (t, J = 8.1 Hz, 1H), 6.54 (d, J = 15.2 Hz, 1H), 5.99 (s, 2H); 13C NMR (151 MHz, CDCl3) δ 148.6 (s), 148.3 (s), 141.8 (s), 129.8 (q, J = 306.0 Hz), 129.5 (s), 122.3 (s), 109.1 (q, J = 3.0 Hz), 108.5 (s), 105.9 (s), 101.4 (s); 19F NMR (564 MHz, CDCl3) δ −43.06 (s). (2-(Naphthalen-2-yl)vinyl)(trifluoromethyl)sulfane (4q).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 62% yield as a yellow oil (31.5 mg) with an E/Z ratio of 94:6: 1H

306.6 Hz), 128.9 (s), 114.7 (q, J = 3.0 Hz), 107.0 (s), 63.2 (s), 14.5 (s); 19F NMR (564 MHz, (CD3)2SO) δ −42.39 (s). (4-(Benzyloxy)styryl)(trifluoromethyl)sulfane (4d).5i By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 57% yield as a white solid (35.3 mg) with an E/Z ratio of 93:7: 1H NMR (600 MHz, (CD3)2SO) δ 7.55 (t, J = 7.8 Hz, 2H), 7.45−7.40 (m, 2H), 7.37 (t, J = 7.5 Hz, 2H), 7.34−7.27 (m, 1H), 7.16 (d, J = 15.2 Hz, 1H), 7.03−6.98 (m, 2H), 6.89 (d, J = 15.1 Hz, 1H), 5.12 (d, J = 5.4 Hz, 2H); 13C NMR (151 MHz, (CD3)2SO) δ 159.4 (s), 143.4 (s), 136.8 (s), 130.2 (s), 129.7 (q, J = 306.1 Hz), 128.9 (s), 128.4 (s), 127.9 (s), 115.1 (s), 107.3 (q, J = 3.0 Hz), 69.4 (s); 19F NMR (564 MHz, (CD3)2SO) δ −42.20 (s). 4-(2-((Trifluoromethyl)thio)vinyl)phenyl Acetate (4e).5i By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:15) and obtained in 67% yield as a yellow oil (35.1 mg) with an E/Z ratio of 94:6: 1H NMR (600 MHz, CDCl3) δ 7.68 (d, J = 8.4 Hz, 2H), 7.25 (d, J = 15.3 Hz, 1H), 7.18 (d, J = 8.3 Hz, 2H), 7.15−7.08 (m, 1H), 2.30 (d, J = 4.9 Hz, 3H); 13C NMR (151 MHz, (CD3)2SO) δ 169.0 (s), 151.2 (s), 141.3 (s), 132.4 (s), 128.7 (q, J = 306.1 Hz), 128.4 (s), 122.3 (s), 110.8 (q, J = 3.1 Hz), 20.9 (s); 19F NMR (564 MHz, CDCl3) δ −37.11 (s). (4-Fluorostyryl)(trifluoromethyl)sulfane (4f).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 58% yield as a yellow oil (25.7 mg) with an E/Z ratio of 96:4: 1H NMR (600 MHz, (CD3)2SO) δ 7.68−7.63 (m, 2H), 7.26−7.17 (m, 3H), 7.06 (t, J = 11.5 Hz, 1H); 13C NMR (151 MHz, (CD3)2SO) δ 163.4 (s), 161.8 (s), 141.2 (s), 131.4 (s), 129.4 (d, J = 307.9 Hz), 115.8 (s), 110.5 (dd, J = 5.5, 2.9 Hz); 19F NMR (564 MHz, (CD3)2SO) δ −41.83 (s), −111.65 (tt, J = 8.9, 5.5 Hz). (3-Chlorostyryl)(trifluoromethyl)sulfane (4g).5h By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 51% yield as a yellow oil (24.2 mg) with an E/Z ratio of 96:4: 1H NMR (600 MHz, (CD3)2SO) δ 7.76 (s, 1H), 7.55 (t, J = 3.8 Hz, 1H), 7.43−7.36 (m, 2H), 7.27 (t, J = 11.5 Hz, 1H), 7.16 (d, J = 15.4 Hz, 1H); 13C NMR (151 MHz, (CD3)2SO) δ 139.5 (s), 137.0 (s), 133.8 (s), 130.7 (s), 129.8 (q, J = 307.9 Hz), 129.0 (s), 126.8 (s), 126.1(s), 113.5 (q, J = 3.2 Hz); 19F NMR (564 MHz, (CD3)2SO) δ −36.70 (s). (2-Methylstyryl)(trifluoromethyl)sulfane (4h).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 60% yield as a colorless oil (26.1 mg) with an E/Z ratio of 93:7: 1H NMR (600 MHz, CDCl3) δ 7.43 (d, J = 7.5 Hz, 1H), 7.29−7.16 (m, 4H), 6.64 (d, J = 15.2 Hz, 1H), 2.37 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 139.3 (s), 135.9 (s), 134.2 (s), 130.6 (s), 129.6 (q, J = 307.9 Hz), 129.0 (s), 126.3 (s), 125.9 (s), 112.8 (d, J = 3.0 Hz), 19.7 (s); 19F NMR (564 MHz, CDCl3) δ −42.83 (s). (2-Methoxystyryl)(trifluoromethyl)sulfane (4i).5h By following the general procedure, the product was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1:50) and obtained in 62% yield as a yellow oil (29.0 mg) with an E/Z ratio of 96:4: 1H NMR (600 MHz, CDCl3) δ 7.38 (d, J = 7.6 Hz, 1H), 7.30 (dd, J = 12.3, 5.4 Hz, 1H), 6.95 (t, J = 7.5 Hz, 1H), 6.90 (d, J = 8.3 Hz, 1H), 6.83 (d, J = 15.4 Hz, 1H), 3.87 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 157.1 (s), 136.8 (q, J = 1.8 Hz), 130.3 (s), 129.8 (q, J = 305.8 Hz), 128.0 (s), 124.0 (s), 120.7 (s), 112.3 (q, J = 3.0 Hz), 111.0 (s), 55.4 (s), 19F NMR (564 MHz, CDCl3) δ −42.90 (s). (3-Methylstyryl)(trifluoromethyl)sulfane (4j).10 By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 62% yield as a yellow oil (27.0 mg) with an E/Z ratio of 94:6: 1H NMR (600 MHz, CDCl3) δ 7.26 (t, J = 7.5 Hz, 1H), 7.23−7.18 (m, 1H), 7.15 (d, J = 7.5 Hz, 1H), 6.98 (d, J = 15.3 Hz, 1H), 6.72 (d, J = 15.3 Hz, 1H), 2.37 (d, J = 6.9 Hz, 1H); 13C NMR (151 MHz, CDCl3) δ 141.5 (s), 138.5 (s), 135.0 (s), 130.6 (s), 129.7 (q, J = 307.9 Hz), 128.7 (s), 127.4 (s), 124.0 (s), 111.3 (q, J = 3.1 Hz), 21.3 (s); 19F NMR (564 MHz, CDCl3) δ −42.82 (s). 503

DOI: 10.1021/acs.joc.7b02232 J. Org. Chem. 2018, 83, 499−504

Note

The Journal of Organic Chemistry NMR (600 MHz, (CD3)2SO) δ 8.19 (d, J = 8.2 Hz, 1H), 7.99 (t, J = 10.4 Hz, 1H), 7.94 (t, J = 8.9 Hz, 2H), 7.83 (d, J = 7.2 Hz, 1H), 7.63− 7.48 (m, 3H), 7.15−7.08 (m, 1H); 13C NMR (151 MHz, (CD3)2SO) δ 138.4 (s), 133.3 (s), 131.9 (s), 130.8 (s), 130.3 (s), 129.7 (q, J = 307.9 Hz), 128.6 (s), 126.9 (s), 126.3 (s), 125.7 (s), 124.7 (s), 123.4 (s), 113.7 (q, J = 3.1 Hz); 19F NMR (564 MHz, (CD3)2SO) δ −41.68 (s). ((9H-Fluoren-9-ylidene)methyl)(trifluoromethyl)sulfane (4r). By following the general procedure, the product was purified by flash column chromatography on silica gel (petroleum ether) and obtained in 54% yield as a yellow oil (30.0 mg): 1H NMR (600 MHz, (CD3)2SO) δ 8.06 (d, J = 7.6 Hz, 1H), 7.90 (d, J = 7.5 Hz, 1H), 7.86 (d, J = 7.7 Hz, 1H), 7.83 (d, J = 7.5 Hz, 1H), 7.78 (s, 1H), 7.46 (t, J = 7.5 Hz, 1H), 7.39 (t, J = 7.7 Hz, 2H), 7.32 (t, J = 7.5 Hz, 1H); 13C NMR (151 MHz, (CD3)2SO) δ 140.8 (s), 138.3 (s), 137.1 (s), 135.0 (s), 130.1 (s), 129.7 (q, J = 307.9 Hz), 129.6 (s), 129.1 (s), 128.4 (s), 127.7 (d, J = 12.7 Hz), 125.4 (s), 121.6 (s), 120.6 (s), 120.1 (s), 111.5 (q, J = 3.0 Hz); 19F NMR (564 MHz, (CD3)2SO) δ −41.23 (s); HRMS calcd for C15H10F3S [M + H]+ 279.0455, found 279.0972; MS (EI) m/z (%) 51.06 (15.72), 69.06 (24.52), 77.09 (25.92), 89.07 (32.94), 134.11 (15.05), 178.20 (100.00), 179.19 (19.01), 207.15 (39.08), 211.18 (34.12), 280.24 (26.87).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b02232. 1 H, 13C, and 19F NMR spectra for the products, labeling experiment details, and radical-trapping experiment details (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Jun Xu: 0000-0002-2985-6609 Jian-Jun Dai: 0000-0001-7918-0080 Hua-Jian Xu: 0000-0002-0789-3484 Author Contributions ∥

Z.-F.C. and T.-T.T. contributed equally to this work

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (nos. 21371044, 21402036, 21472033, 21571047, and 201502038). We thank Zhuo-Wei Xu and Tao Jia in this group for reproducing the results of compounds 2c, 4d, and 4k.

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REFERENCES

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DOI: 10.1021/acs.joc.7b02232 J. Org. Chem. 2018, 83, 499−504