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Synthesis 2014; 46(05): 607-612
DOI: 10.1055/s-0033-1338578
paper
© Georg Thieme Verlag Stuttgart · New York

Copper/Silver-Mediated Decarboxylative Trifluoromethylation of α,β-Unsaturated Carboxylic Acids with CF3SO2Na

Jun Yin
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P. R. of China   Fax: +86(411)84986295   Email: ymli@dlut.edu.cn
,
Yaming Li*
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P. R. of China   Fax: +86(411)84986295   Email: ymli@dlut.edu.cn
,
Rong Zhang
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P. R. of China   Fax: +86(411)84986295   Email: ymli@dlut.edu.cn
,
Kun Jin
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P. R. of China   Fax: +86(411)84986295   Email: ymli@dlut.edu.cn
,
Chunying Duan*
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P. R. of China   Fax: +86(411)84986295   Email: ymli@dlut.edu.cn
› Author Affiliations
Further Information

Publication History

Received: 18 August 2013

Accepted after revision: 29 November 2013

Publication Date:
17 December 2013 (online)

 
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Abstract

A copper/silver-catalyzed decarboxylative trifluoromethylation of α,β-unsaturated carboxylic acids with CF3SO2Na was performed under relatively mild conditions. The reaction shows high E/Z selectivity and wide substrate tolerance. Ag2CO3 plays an important role in promoting the decarboxylation process.


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Key words

fluorine - transition metals - copper - catalysis - radicals

The introduction of trifluoromethyl (CF3) groups into organic molecules can substantially improve their chemical and metabolic stability, lipophilicity, and binding selectivity as a result of the strong electron-withdrawing nature and large hydrophobic domain of the trifluoromethyl groups.[1] On this basis, there has been a recent surge in the number of reports describing the formation of carbon–trifluoromethyl (C–CF3) bonds.[2] A variety of processes for the construction of Csp3–CF3 bonds have been reported using electrophilic,[3] nucleophilic,[4] and radical-based[5] reagents. However, the construction of Csp2–CF3 bonds, especially Cvinyl–CF3 bonds, is rarely reported. Cross-coupling­ processes can facilitate the construction of Csp2–CF3 bonds under milder reaction conditions, rendering them more amenable to late-stage modification of highly functionalized molecules.[6] Toward this end, a variety of copper-[2a] [7] and palladium-[8] mediated reactions have recently been developed. These transition-metal-catalyzed trifluoromethylations are, however, mainly limited to the installation of Caryl–CF3 groups.

A few approaches to the construction of Cvinyl–CF3 bonds have been reported (Scheme [1]).[9] The processes developed by Liu[9d] and Hu[9c] depend heavily on the use of costly, electrophilic trifluoromethyl reagents, whereas Buchwald’s[9a] [b] and Cho’s[9f] procedures require expensive Pd or Ru catalysts. Herein, we report a new and efficient method for copper-/silver-catalyzed decarboxylative trifluoromethylation of α,β-unsaturated carboxylic acids by using the stable­ and inexpensive reagent sodium trifluoromethanesulfinate (CF3SO2Na, Langlois reagent).

Zoom Image
Scheme 1 Formation of Cvinyl–CF3 bonds

Langlois reagent is an attractive CF3 source. It has been known since 1989 that alkali metal trifluoromethanesulfinates can transfer the CF3 group to CF3 • species that, in turn, can trifluoromethylate electron-rich double bonds and arenes.[10a] Since the original publication, a considerable number of papers have appeared reporting the use of CF3SO2Na and also zinc difluoromethanesulfinate [(CF2HSO2)2Zn, DFMS].[10] In the past several years, decarboxylative couplings of aryl carboxylic acids or their salts have gained interest because they are readily available and inexpensive.[11] An interesting process of Cu/Ag-mediated decarboxylation of cinnamic acid and phenylpropiolic acid was reported by Yang.[12] Our group has also reported the Cu/Ag-mediated trifluoromethylation of aryl iodides.[13] More recently, Liu’s[10i] group reported Cu(II)-catalyzed reaction of cinnamic acid with CF3SO2Na, and Maiti[10j] reported a Fe(III)-catalyzed trifluoromethylation of cinnamic acid. However neither Liu’s nor Maiti’s work apply to halogenated compounds or α,β-unsaturated carboxylic acid compounds that are substituted at the β-position with methyl or phenyl groups. Inspired by the process mentioned above, we wondered whether the Cu/Ag catalyst system could be active in the trifluoromethylation of α,β-unsaturated carboxylic acids.

At the outset of this investigation, we screened the combinations of transition-metal catalysts, additives, and solvents that were essential for the trifluoromethylation of cinnamic acid (Table [1]; for details see the Supporting Information). Initially, we speculated that Ag2CO3 should be the best additive because of the release of CO2 during the formation of silver cinnamate. Indeed, as expected, the use of AgOTf, AgNO3, or Ag2O as additives in place of Ag2CO3 did not improve the yield, affording 2c in only 31–63% yields (Table [1], entries 1–6). It was found that the use of 0.6 equiv Ag2CO3 was sufficient to complete the reaction, further reducing the amount of Ag2CO3 resulted in a significant decrease in the yield (Table [1], entries 7 and 8). CuCl2·H2O and CuCl turned out to be equally effective, whereas other Cu salts such as CuI, CuO, Cu, or Cu2O were less effective than CuCl (Table [1], entries 9–13). It was necessary to use 20 mol% CuCl for complete conversion (Table [1], entries 14 and 15). The yield decreased dramatically when the temperature was increased to 90 °C, but only declined slightly when the reaction was conducted at 50 °C (22 and 81%, respectively; Table [1], entries 16 and 17). The use of 1,2-dichloroethane (DCE) proved to be more efficient than other solvents such as methanol, acetonitrile, or N-methyl-2-pyrrolidinone (NMP) (see the Supporting Information). The desired product was obtained in 89% yield by using 5 equivalents tert-butyl hydroperoxide (TBHP). However, addition of 3 or 7 equivalents TBHP led to generation of the product in 47 and 90% yields, respectively (see the Supporting Information). Finally, control experiments showed that Cu catalyst and Ag additives were both necessary for the reaction to proceed (Table [1], entries 18 and 19). Ag2CO3 promoted the reaction greatly, since it makes the decarboxylation process much easier.

Table 1 Optimization of the Conditionsa

Entry

Catalyst (mol%)

Additives (equiv)

Yield (%)b

 1

CuCl (20)

Ag2CO3 (1.0)

89

 2

CuCl (20)

AgOTf (2.0)

48

 3

CuCl (20)

AgNO3 (2.0)

36

 4

CuCl (20)

Ag2O (1.0)

62

 5

CuCl (20)

AgOAc (2.0)

63

 6

CuCl (20)

AgI (2.0)

31

 7

CuCl (20)

Ag2CO3 (0.6)

89

 8

CuCl (20)

Ag2CO3 (0.5)

67

 9

CuI (20)

Ag2CO3 (0.6)

46

10

CuO (20)

Ag2CO3 (0.6)

45

11

Cu (20)

Ag2CO3 (0.6)

79

12

Cu2O (20)

Ag2CO3 (0.6)

82

13

CuCl2·H2O (20)

Ag2CO3 (0.6)

88

14

CuCl (10)

Ag2CO3 (0.6)

77

15

CuCl (40)

Ag2CO3 (0.6)

83

16c

CuCl (20)

Ag2CO3 (0.6)

22

17d

CuCl (20)

Ag2CO3 (0.6)

81

18

CuCl (20)

–

32

19

–

Ag2CO3 (0.6)

40

a Reaction conditions: 1c (0.1 mmol), CF3SO2Na (0.3 mmol), TBHP (70% aqueous, 0.5 mmol), DCE (2 mL), 70 °C, 24 h.

b Yields were determined by GC analysis.

c The reaction was conducted at 90 °C.

d The reaction was conducted at 50 °C.

With the optimized conditions in hand, we next explored the substrate scope (Scheme [2]). By using the standard conditions, a series of α,β-unsaturated carboxylic acids were treated with CF3SO2Na and TBHP, and the reaction proceeded smoothly to produce the desired compounds 2a–m in 48–72% yield. Among the various cinnamic acid derivatives, electron-rich cinnamic acids bearing a meth­oxyl group were particularly favorable, generating the desired products in yields of more than 65% (2a and 2b), whereas others gave lower — yet still synthetically useful — yields. Polysubstituted cinnamic acids are more reactive than monosubstituted derivatives. The yield of the isolated product 2c (52%) was lower than that determined by GC because of the volatility of the product. It is worth mentioning that halogenated acrylic acids also gave the desired products in moderate yields (2e, 2f, 2i, and 2j), which are useful for further chemical conversion in, for example, Heck and Suzuki reactions. When methyl and phenyl groups were introduced into the β-position of the α,β-unsaturated carboxylic acid, the decarboxylative trifluoromethylation could be performed more efficiently (2g–k). Notably, the trifluoromethylation reaction was also found to be stereoselective, with the CF3-functionalized alkenes being formed with an E/Z ratio ranging from 94:6 to more than 99:1.

Zoom Image
Scheme 2 Copper-catalyzed decarboxylative trifluoromethylation of cinnamic acids with sodium trifluoromethanesufinate. Reagents and conditions: 1 (0.2 mmol), CF3SO2Na (0.6 mmol), CuCl (0.04 mmol), Ag2CO3 (0.12 mmol), TBHP (1.0 mmol, 70% aqueous), DCE (2 mL), 70 °C, 24 h; isolated yields, except for 2m (GC/MS yield); E/Z ratios were determined by 19F NMR analysis.
Zoom Image
Scheme 3 Capture of CF3 radical by TEMPO

A detailed mechanism remains to be elucidated. On the basis of the previous work on the trifluoromethylation of aromatics[10] and copper-catalyzed C–P coupling of cinnamic acids,[12] it is reasonable that the reaction proceeds through a route that involves radical species. To gain insight into the mechanism of this reaction, a radical scavenger 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was added under the standard reaction conditions (Scheme [3]). The result indicated that only a trace amount of 2c was formed and TEMPO-CF3 was formed in 60% yield (detected by GC/MS) when 3.0 equivalents of TEMPO­ were added.

Based on above experimental results, we concluded that the CF3 radical is involved in the transformation (Scheme [4]). The reaction starts with the decarboxylation of cinnamic acid under Ag2CO3, forming an alkenyl–silver species A. Compound A would then transfer the alkenyl group to copper by transmetallation to give the organocopper intermediate B. In parallel, the trifluoromethyl radical will be generated by the reaction of tert-butyl hydroperoxide with NaSO2CF3. Addition of the trifluoromethyl radical at the α-position of the double bond in cupric cinnamate would give complex C. Finally, the desired product would be released, generating the Cu(I) species. Oxidation of Cu(I) by tert-butyl hydroperoxide would regenerate the Cu(II) species and resume the catalytic cycle, which explains the initial experimental result that CuCl2·H2O and were equally effective.

Zoom Image
Scheme 4 Proposed mechanism for vinylic trifluoromethylation

In conclusion, we have developed a protocol for the construction of Cvinyl–CF3 bonds through a Cu/Ag-catalyzed decarboxylative trifluoromethylation of α,β-unsaturated carboxylic acid derivatives with CF3SO2Na. This reaction proceeds well for a wide range of α,β-unsaturated carboxylic acids (including alkyl- and aryl- substituted derivatives) with excellent E/Z selectivity. The inclusion of Ag2CO3 additives was crucial for promoting the decarboxylation of α,β-unsaturated carboxylic acids.

Unless otherwise noted, all reagents were obtained from commercial sources and used without further purification. Thin-layer chromatography (TLC) was performed by using commercially prepared 60 mesh silica gel plates visualized with short-wavelength UV light (254 nm). The products were isolated by column chromatography on silica gel (300–400 mesh size) by using petroleum ether (PE; 60–90 °C) and EtOAc as eluents. All compounds were characterized by 1H, 13C and 19F NMR spectroscopic analysis. 1H, 13C and 19F NMR spectra were recorded with an INOVA 400 instrument with an operating frequency of 400, 100 and 377 MHz, respectively. Chemical shifts for 1H NMR spectra are reported in ppm relative to TMS. The following abbreviations are used to indicate multiplicities: s = singlet, d = doublet, t = triplet, dd = doublet of doublets, dq = doublet of quartets, m = multiplet. Coupling constants (J) are reported in hertz (Hz). Gas chromatography analyses were performed with an FID detector. High-resolution mass spectrometry (HRMS) data were performed with an Q-Tof MS instrument.


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Preparation of α,β-Unsaturated Carboxylic Acids 1; Typical Procedure[14]

A 100 mL two-necked, round-bottom flask equipped with a magnetic stir bar, thermometer, and condenser, was charged with triethyl phosphonoacetate (1.344 g, 6 mmol) followed by THF (20 mL). The flask was cooled to 5 °C and NaH (60% in mineral oil, 265 mg, 6.6 mmol) was added in portions over 10 min. The flask was warmed to about 25 °C and to this clear solution was added 4-methoxy­benzaldehyde (816 mg, 6 mmol) by addition funnel. The flask was heated to reflux for 8 h, then the reaction was cautiously quenched by the slow addition of H2O (Caution: Vigorous gas evolution!). The contents of the flask were then poured into H2O and extracted with Et2O and washed with 0.1 N HCl and brine. The solvent was removed to afford a crude oil. A 50 mL single-neck round-bottom flask was charged with the obtained oil, THF (2 mL), and 2 M NaOH (2.4 mL, 4.8 mmol) and heated at reflux for 3 h. The contents were diluted with Et2O and acidified with conc. HCl, extracted twice with Et2O, washed with brine, dried over MgSO4, filtered, and concentrated to obtain 1a (540 mg; 97% purity GC) as a white solid.


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Decarboxylative Trifluoromethylation of α,β-Unsaturated Acids­ (Scheme [2]); General Procedure

To a solution of substrate 1 (0.2 mmol, 1 equiv), CuCl (4 mg, 0.04 mmol, 1 equiv), Ag2CO3 (33 mg, 0.12 mmol, 0.6 equiv), and NaSO2CF3 (93.6 mg, 0.6 mmol, 3.0 equiv) in DCE (2 mL) at 0 °C, was slowly added TBHP (70% in water, 136 μL, 1.0 mmol, 5.0 equiv) with stirring. The reaction was allowed to warm to 70 °C and then stirred for 24 h. The resulting mixture was extracted with EtOAc­ (3 × 8 mL) and the combined organic layers were dried with Na2SO4 and then concentrated under vacuum. After evaporation, the residue was purified by column chromatography using silica gel (300–400 mesh; PE–EtOAc, 100:1→20:1).


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(E)-1-Methoxy-4-(3,3,3-trifluoroprop-1-en-1-yl)benzene (2a)[10i]

Yield: 26.3 mg (65%); white solid; mp 37–39 °C.

1H NMR (400 MHz, CDCl3): δ = 7.39 (d, J = 8.7 Hz, 2 H), 7.08 (dd, J = 16.1, 1.9 Hz, 1 H), 6.90 (d, J = 8.7 Hz, 2 H), 6.06 (dq, J = 16.1, 6.5 Hz, 1 H), 3.83 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.19, 137.25 (q, J = 6.8 Hz), 129.19, 126.0, 123.9 (q, J = 266.3 Hz), 114.5, 113.5 (q, J = 31.5 Hz), 55.53.

19F NMR (377 MHz, CDCl3): δ = –63.29 (dd, J = 6.5, 1.8 Hz).

MS (EI): m/z = 202.0 [M]+.


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(E)-1,2,3-Trimethoxy-5-(3,3,3-trifluoroprop-1-en-1-yl)benzene (2b)[10j]

Yield: 37.8 mg (72%); white solid; mp 61–63 °C.

1H NMR (400 MHz, CDCl3): δ = 7.05 (dd, J = 16.0, 2.0 Hz, 1 H), 6.65 (s, 2 H), 6.10 (dq, J = 16.0, 6.5 Hz, 1 H), 3.86 (br, 9 H).

13C NMR (100 MHz, CDCl3): δ = 153.64, 139.87, 137.79 (q, J = 13.0, 6.2 Hz), 129.09, 123.8 (q, J = 269.7 Hz), 115.54 (q, J = 33.4 Hz), 104.82, 61.13, 56.32.

19F NMR (377 MHz, CDCl3): δ = –63.53 (dd, J = 6.4, 1.8 Hz).

MS (EI): m/z = 262.1 [M]+.


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(E)-(3,3,3-Trifluoroprop-1-en-1-yl)benzene (2c)[15a]

Yield: 17.9 mg (52%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.45 (d, J = 3.6 Hz, 2 H), 7.41–7.37 (m, 3 H), 7.15 (dd, J = 16.0, 1.8 Hz, 1 H), 6.20 (dq, J = 16.0, 6.5 Hz, 1 H).

13C NMR (100 MHz, CDCl3): δ = 137.83 (q, J = 6.4 Hz), 133.57, 130.18, 129.10, 127.69, 123.8 (q, J = 269 Hz), 116.01 (q, J = 33.8 Hz).

19F NMR (377 MHz, CDCl3): δ = –63.78 (dd, J = 6.3, 1.5 Hz).

MS (EI): m/z = 172.1 [M]+.


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(E)-1-Methyl-4-(3,3,3-trifluoroprop-1-en-1-yl)benzene (2d)[10i]

Yield: 20.1 mg (54%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.34 (d, J = 8.0 Hz, 2 H), 7.19 (d, J = 8.0 Hz, 2 H), 7.11 (dd, J = 16.1, 1.9 Hz, 1 H), 6.14 (dq, J = 16.1, 6.6 Hz, 1 H), 2.37 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 140.42, 137.67 (q, J = 6.6 Hz), 130.78, 129.75, 127.60, 123.9 (q, J = 269 Hz), 114.89 (q, J = 33.6 Hz), 29.88.

19F NMR (377 MHz, CDCl3): δ = –63.51 to –63.64 (m).

MS (EI): m/z = 186.2 [M]+.


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(E)-1-Chloro-4-(3,3,3-trifluoroprop-1-en-1-yl)benzene (2e)[9e]

Yield: 24.0 mg (58%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.37 (m, 4 H), 7.10 (dd, J = 16.1, 2.0 Hz, 1 H), 6.18 (dq, J = 16.1, 6.4 Hz, 1 H).

13C NMR (100 MHz, CDCl3): δ = 136.55 (q, J = 6.7 Hz), 136.12, 132.02, 129.35, 128.88, 122.22 (q, J = 270 Hz), 116.59 (q, J = 34.1 Hz).

19F NMR (377 MHz, CDCl3): δ = –63.80 to –64.08 (m).

MS (EI): m/z = 206.5 [M]+.


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(E)-1-Bromo-4-(3,3,3-trifluoroprop-1-en-1-yl)benzene (2f)[15b]

Yield: 24.1 mg (48%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.53 (d, J = 8.3 Hz, 2 H), 7.32 (d, J = 8.3 Hz, 2 H), 7.09 (dd, J = 16.1, 2.0 Hz, 1 H), 6.21 (dq, J = 16.1, 6.4 Hz, 1 H).

13C NMR (100 MHz, CDCl3): δ = 136.66 (q, J = 6.7 Hz), 132.48, 132.34, 129.13, 123.6 (q, J = 270 Hz), 124.42, 116.72 (q, J = 33.8 Hz).

19F NMR (377 MHz, CDCl3): δ = –63.93 (dd, J = 6.3, 1.7 Hz).

MS (EI): m/z = 251.0 [M]+.


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(E)-(4,4,4-Trifluorobut-2-en-2-yl)benzene (2g)[15c]

Yield: 21.2 mg (57%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.41 (d, J = 6.7 Hz, 2 H), 7.39–7.34 (m, 3 H), 5.87 (q, J = 8.4 Hz, 1 H), 2.29 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 149.21 (q, J = 5.2 Hz), 141.01, 129.182, 128.768, 126.23, 123.88 (q, J = 281.9 Hz), 116.10 (q, J = 33.8 Hz), 17.57.

19F NMR (377 MHz, CDCl3): δ = –57.51 (dd, J = 8.4, 2.0 Hz).

MS (EI): m/z = 186.1 [M]+.


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(E)-1-Methyl-4-(4,4,4-trifluorobut-2-en-2-yl)benzene (2h)

Yield: 24.0 mg (60%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.31 (d, J = 8.0 Hz, 2 H), 7.17 (d, J = 8.0 Hz, 2 H), 5.85 (q, J = 8.4 Hz, 1 H), 2.36 (s, 3 H), 2.27 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 148.98 (q, J = 5.3 Hz), 139.27, 138.02, 129.43, 126.11, 124.01 (q, J = 271.7 Hz), 115.25 (q, J = 33.3 Hz), 21.31, 17.47.

19F NMR (377 MHz, CDCl3): δ = –57.27 (dd, J = 8.5, 1.9 Hz).

MS (EI): m/z = 200.2 [M]+.

HRMS (EI-TOF): m/z [M]+ calcd for C11H11F3: 200.0813; found: 200.0814.


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(E)-1-Chloro-4-(4,4,4-trifluorobut-2-en-2-yl)benzene (2i)

Yield: 28.2 mg (64%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.35 (m, 4 H), 5.87 (q, J = 8.4 Hz, 1 H), 2.27 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 147.99 (q, J = 5.7 Hz), 139.31, 135.20, 128.95, 127.55, 123.66 (q, J = 271.8 Hz), 116.50 (q, J = 34.3 Hz), 17.52.

19F NMR (377 MHz, CDCl3): δ = –57.59 (dd, J = 8.3, 1.8 Hz).

MS (EI): m/z = 220.6 [M]+.

HRMS (EI-TOF): m/z [M]+ calcd for C10H8ClF3: 220.0267; found: 220.0266.


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(E)-1-Chloro-4-(3,3,3-trifluoro-1-phenylprop-1-en-1-yl)benzene (2j)[15d]

Yield: 35.0 mg (62%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.40–7.28 (m, 5 H), 7.24–7.16 (m, 4 H), 6.12 (q, J = 8.2 Hz, 1 H).

13C NMR (100 MHz, CDCl3): δ = 152.04 (q, J = 5.7 Hz), 139.82, 137.85, 135.79, 134.85, 130.69, 129.317, 128.82, 128.22, 123.1 (q, J = 270 Hz), 116.15 (q, J = 33.3 Hz).

19F NMR (377 MHz, CDCl3): δ = –56.09 (dd, J = 46.5, 8.2 Hz).

MS (EI): m/z = 282.5 [M]+.


#

(3,3,3-Trifluoroprop-1-ene-1,1-diyl)dibenzene (2k)[15d]

Yield: 29.8 mg (60%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.40–7.29 (m, 6 H), 7.24 (m, 4 H), 6.12 (q, J = 8.3 Hz, 1 H).

13C NMR (100 MHz, CDCl3): δ = 152.63 (q, J = 5.6 Hz), 140.29, 137.43, 129.03, 128.17, 124.60 (q, J = 270 Hz), 115.77 (q, J = 33.2 Hz).

19F NMR (377 MHz, CDCl3): δ = –56.04 (d, J = 8.3 Hz).

MS (EI): m/z = 248.1 [M]+.


#

(E)-4-(3,3,3-Trifluoroprop-1-en-1-yl)phenol (2l)[10i]

Yield: 23.7 mg (63%); light-yellow solid; mp 71.2–72.5 °C.

1H NMR (400 MHz, CDCl3): δ = 7.34 (d, J = 8.5 Hz, 2 H), 7.07 (dd, J = 16.1, 2.0 Hz, 1 H), 6.84 (d, J = 8.5 Hz, 2 H), 6.05 (dq, J = 16.1, 6.6 Hz, 1 H), 5.36 (s, 1 H).

13C NMR (100 MHz, CDCl3): δ = 157.33, 137.21 (q, J = 6.8 Hz), 129.44, 126.57, 124.07 (q, J = 268.5 Hz), 116.04, 113.80 (q, J = 33.7 Hz).

19F NMR (376 MHz, CDCl3): δ = –62.89 (s).

MS (EI): m/z = 188.1 [M]+.


#

(E)-2-(4,4,4-Trifluorobut-2-en-2-yl)thiophene (2m)

Yield: 20.0 mg (52%); colorless liquid.

1H NMR (400 MHz, CDCl3): δ = 7.31 (d, J = 5.0 Hz, 1 H), 7.23 (d, J = 3.2 Hz, 1 H), 7.06–7.00 (m, 1 H), 6.01 (q, J = 8.4 Hz, 1 H), 2.31 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 143.86 (s), 141.74 (q, J = 5.7 Hz), 127.98 (s), 126.84 (s), 126.31 (s), 123.86 (q, J = 270.0 Hz), 113.40 (q, J = 33.7 Hz), 17.22 (s).

HRMS (EI-TOF): m/z [M]+ calcd for C8H7F3S: 192.0221; found: 192.0221.


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Acknowledgment

This work was supported by the National Natural Science Foundation of China (Project No. 21176039 and 20923006).

Supporting Information

    for this article is available online at http://www.thieme-connect.com.accesdistant.sorbonne-universite.fr/ejournals/toc/synthesis.
  • Supporting Information


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Zoom Image
Scheme 1 Formation of Cvinyl–CF3 bonds
Zoom Image
Scheme 2 Copper-catalyzed decarboxylative trifluoromethylation of cinnamic acids with sodium trifluoromethanesufinate. Reagents and conditions: 1 (0.2 mmol), CF3SO2Na (0.6 mmol), CuCl (0.04 mmol), Ag2CO3 (0.12 mmol), TBHP (1.0 mmol, 70% aqueous), DCE (2 mL), 70 °C, 24 h; isolated yields, except for 2m (GC/MS yield); E/Z ratios were determined by 19F NMR analysis.
Zoom Image
Scheme 3 Capture of CF3 radical by TEMPO
Zoom Image
Scheme 4 Proposed mechanism for vinylic trifluoromethylation