Synthesis of propargylic and allylic trifluoromethyl selenoethers by copper-mediated trifluoromethylselenolation of propargylic chlorides and allylic bromides

Tetrahedron 70 (2014) 8872e8878

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Synthesis of propargylic and allylic trifluoromethyl selenoethers by copper-mediated trifluoromethylselenolation of propargylic chlorides and allylic bromides Mingguang Rong y, Ronglu Huang y, Yi You *, Zhiqiang Weng * Department of Chemistry, Fuzhou University, Fuzhou 350108, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 July 2014 Received in revised form 17 September 2014 Accepted 29 September 2014 Available online 5 October 2014

The copper-mediated trifluoromethylselenolation of propargylic chlorides and allylic bromides is described. This approach provides a wide range of propargylic and allylic trifluoromethyl selenoethers in moderate to good yields. These results open the way to synthesis strategies for various trifluoromethylselenolated compounds. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Trifluoromethylthiolation Trifluoromethylselenolation Copper Propargylic trifluoromethyl selenoethers Allylic trifluoromethyl selenoethers

1. Introduction Currently there is considerable interest in the discovery and development of organic molecules containing perfluoroalkylated groups because of their unusual chemical and physical properties.1,2 Of particular importance is the trifluoromethylthiosubstituted derivatives, which are potential synthetic precursor for the construction of complicated biologically active compounds.3,4 Generally, the trifluoromethylthiolated compounds are produced from the nucleophilic,5 electrophilic,6 and radical7 trifluoromethylation of disulfides, thiocyanates, thiols, and thiolates with a trifluoromethylation reagent. Several new synthetic strategies8,9 have been developed in recent years, including the transition-metal-catalyzed trifluoromethylthiolation of aryl halides,10 vinyl iodides,11 aryl boronic acids,12 and arenes13 to give the corresponding products. These transformations provide efficient and flexible means to synthesize trifluoromethylthio-substituted derivatives.14 However, in contrast to the well-developed trifluoromethylthiolation, considerably less effort has been devoted to the development of preparing CeSeCF3 bonds,5,15 despite the trifluoromethylseleno group has similar beneficial effects as the

* Corresponding authors. Tel./fax: þ86 59122866121; e-mail address: zweng@ fzu.edu.cn (Z. Weng). y These authors contributed equally. http://dx.doi.org/10.1016/j.tet.2014.09.091 0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

trifluoromethylthio group.16 Most of these procedures involve the trifluoromethylation of selenium-containing compounds such as selenocyanates, and diselenides. Unfortunately, these methods are limited owing to their demand for the use of specific starting materials, toxic or unstable reagents. Recently, our group has developed a concise synthetic route to synthesize an air stable trifluoromethylselenolated copper reagent [(bpy)Cu(SeCF3)]2 (1). The nucleophilic trifluoromethylselenolation of aryl and alkyl halides with 1 gave the corresponding trifluoromethylselenolated products in good yields.17 This approach was also successfully extended to the trifluoromethylselenolation of a-halo-a,b-unsaturated carbonyl substrates to yield the corresponding a-trifluoromethylseleno-a,b-unsaturated carbonyl compounds.18 Based on this work, we investigated further coppermediated trifluoromethylselenolation of propargylic chlorides. The propargylic subunit constitutes a structural motif shared by various natural products, fine chemicals, and synthetic pharmaceuticals.19 Transition-metal-mediated propargylic substitution of propargylic alcohol derivatives and halides has become an important synthetic tool for the construction of CeC and CeX (heteroatom) bonds at the propargylic position.20 However, there have been very few reports of copper-mediated trifluoromethylation of 22 propargyl halides. For example, the Shibata21 and the Szabo groups independently reported copper-mediated trifluoromethylation of propargylic halides and trifluoroacetates with S-(trifluoromethyl)diphenylsulfonium salt and (PPh3)3Cu(CF3),

M. Rong et al. / Tetrahedron 70 (2014) 8872e8878

respectively. The Nishibayashi group described a copper-catalyzed nucleophilic trifluoromethylation of propargylic halides with CF3SiMe3.23 Recently, we have also developed copper-catalyzed trifluoromethylthiolation of propargylic chlorides with elemental sulfur and CF3SiMe3, affording propargylic trifluoromethyl thioethers in good yields.24 Given the importance of trifluoromethylselenolated compounds,25 procedures that allow for the preparation of trifluoromethylselenolated propargylic products in high yield under mild conditions are of great interest in synthetic organic chemistry. We report herein the copper-mediated trifluoromethylselenolation of propargylic chlorides and allylic bromides with [(bpy) Cu(SeCF3)]2 (1) leading to propargylic and allylic trifluoromethyl selenoethers.

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With the optimum reaction conditions, we next investigated the trifluoromethylselenolation of various propargylic chlorides. The results are summarized in Table 2. Table 2 Trifluoromethylselenolation of propargylic chlorides (2) by [(bpy)Cu(SeCF3)]2 1a

Entry

Propargylic chlorides

Product

Yieldb (%)

1

83

2

56

3

75

4

80c

5

66c

6

67

7

68c

8

70

9

47

10

53

11

59

12

48

13

68

2. Results and discussion Initially, the reaction of [(bpy)Cu(SeCF3)]2 (1) with (3chloroprop-1-ynyl)benzene (2a) was examined to screen the optimized reaction conditions. Acetonitrile solvent had been demonstrated to possess unique properties in previously reported copper-mediated trifluoromethylthiolation26 and trifluoromethylselenolation17 of aryl or alkyl halides. When we treated 2a with 1 in CH3CN at 70  C for 16 h, we were delighted to see that the desired product 3a could be formed in 78% yield based on 2a (Table 1, entry 1). In an attempt to improve the overall yield of the trifluoromethylselenolation, we evaluated the role of different parameters such as solvent, reaction temperature, and time. Among the various solvents tested under otherwise identical conditions, DMF and NMP afforded the best results (Table 1, entries 3 and 4), whereas other solvents such as DMSO, THF, dioxane, DME, and CH2Cl2 gave lower yields (entries 2, 6e8, and 10). Additionally, the reaction was dramatically retarded by use of methanol and toluene as solvents, presumably due to the instability or poor solubility of 1 in these solvents (entries 5 and 9). We next focused our attention on the reaction temperature effect. A decrease of the reaction temperature (50  C) in DMF led to a lower yield (77%; entry 11), and increasing the temperature to 90  C also resulted in a dramatic decrease in yield (49%; entry 12). The effect of reaction time was also investigated in DMF. Reducing the reaction time to 8 h led to incomplete conversion (40%; entry 13). On the basis of these results, entry 3 was found to be the best conditions. Table 1 Optimization of the Cu-mediated trifluoromethylselenolation of 1-(3-chloroprop-1ynyl)-4-methylbenzenea

Entry

Solvent

T ( C)

Time (h)

Yieldb (%)

1 2 3 4 5 6 7 8 9 10 11 12 13

CH3CN DMSO DMF NMP CH3OH THF Dioxane DME Toluene CH2Cl2 DMF DMF DMF

70 70 70 70 70 70 70 70 70 40 50 90 70

16 16 16 16 16 16 16 16 16 16 16 16 8

78 74 83 89 16 64 43 78 10 44 77 49 40

a Reaction conditions: 1 (0.060 mmol), 2a (0.10 mmol), solvent (1.5 mL), under N2 atmosphere, DMSO¼dimethyl sulfoxide, DMF¼N,N-dimethylformamide, NMP¼Nmethylpyrrolidone, DME¼1,2-dimethoxyethane. b The yield was determined by 19F NMR spectroscopy with PhOCF3 as internal standard.

a

Reaction conditions: 1 (0.24 mmol), 2 (0.40 mmol), DMF (4.0 mL). Isolated yields. c The yield was determined by 19F NMR spectroscopy with PhOCF3 as internal standard. b

The propargylic chlorides (2beh) bearing para- or meta-alkylsubstituted aromatic rings all worked well in this reaction to give the corresponding products 3beh in 56e80% yield (Table 2, entries

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2e8). Furthermore, the propargylic chlorides (2iek) having an electron-withdrawing (CF3) group or electron-donating (MeO, nAmO) group on the benzene ring could participate nicely in the trifluoromethylselenolation to furnish the desired products 3iek in moderate yields (47%, 53%, and 59%, respectively; Table 2, entries 9e11). Similarly, the trifluoromethylselenolation was also effective for the reaction of 1 with propargylic chlorides (2l and 2m) having para-halogen-substituted phenyl rings, affording trifluoromethylselenolated products 3l and 3m in 48% and 68% yields, respectively (Table 2, entries 12 and 13). It is notable that the chloro moiety on the aromatic ring was tolerated under these reaction conditions and offers versatile synthetic functionality for further elaboration. Encouraged by these results, we attempted to extend the process to trifluoromethylselenolation of allylic bromides (Table 3). In general, the trifluoromethylselenolation proceeded efficiently and regioselectively with various types of substituted cinnamyl bromides to produce the linear allylic regioisomer. The reaction of cinnamyl bromides (4a, 4b, and 4d) with methyl-, isopropyl-, and tert-butyl-substitutions at the para-position of the aromatic rings and 2,4,6-trimethyl-substituted cinnamyl bromide 4c was found to be favored in the trifluoromethylselenolation to afford the

corresponding products 5aee in moderate to good yields (56e82%; Table 3, entries 1e5). In addition, a para-methylthio-substituted cinnamyl bromide 4f smoothly underwent trifluoromethylselenolation to generate the corresponding product 5f in 71% yield (Table 3, entry 6). However, cinnamyl bromide 4g possessing electron-withdrawing substituent on the aromatic ring delivered the corresponding products 5g in somewhat lower yield (41%; Table 3, entry 7). This reaction system has also been applied to the trifluoromethylselenolation of 1 with cyclic allylic bromide 4h. To our delight, the corresponding product 5h could be generated in 91% yield (19F NMR; Table 3, entry 8). Moreover, the geranyl bromide 4i and 4-bromo-3-ethoxy-2-butenoate 4j also underwent smooth reaction to afford the corresponding products 5i and 5j in 62% and 64% yields, respectively (Table 3, entries 9 and 10). To demonstrate the scalability of our methodology, a gram-scale reaction was performed (Scheme 1). The trifluoromethyl selenolation of 2a with 1 proceeded smoothly to furnish trifluoromethylselenolated product 3a with 81% isolated yield in 16 h at 70  C.

Table 3 Trifluoromethylselenolation of allylic bromides 4 by [(bpy)Cu(SeCF3)]2 1a

Entry

Allylic bromides

Product

Scheme 1. Scalability of the trifluoromethylselenolation of 2a.

b

Yield (%)

1

82

2

70

3

61

4

56

5

79

6

71

7

41

8

91c

9

62

10

64

In order to gain some mechanistic insights into the trifluoromethylselenolation, the following experiments were performed (Table 4). The trifluoromethylselenolation of 2a with 1 occurred smoothly with the addition of a stoichiometric amount of cyclohexa-1,4-diene (CHD) as a radical scavenger, affording the corresponding product 3a in 82% yield (19F NMR). However, the addition of other radical scavengers such as 2,2,6,6tetramethylpyridine N-oxide (TEMPO) (1.0 equiv) led to diminished yield (39%) of the desired product 3a. Subsequent experiments showed that copper reagent is prone to decompose in the presence of the radical scavenger TEMPO.22,27 As a consequence, lower yield of 3a was detected. These preliminary studies suggest against a purely free radical pathway in the present coppermediated trifluoromethylselenolation. On the basis of these results, we propose that the reaction probably proceeds through oxidative addition/reductive elimination process involving the intermediacy of the propargylcopper(III) or allylcopper(III) intermediate.24,26b,28 Table 4 Effects of additives on trifluoromethylselenolation of propargylic chloride (2a) with [(bpy)Cu(SeCF3)]2 1a

Entry

Additive (equiv)

Yieldb (%)

1 2

CHD (1.0) TEMPO (1.0)

82 39

Reaction conditions: 1 (0.060 mmol), 2a (0.10 mmol), DMF (1.5 mL), 70  C, 16 h. The yield was determined by 19F NMR spectroscopy with PhOCF3 as internal standard. a

a

Reaction conditions: 1 (0.24 mmol), 4 (0.40 mmol), DMF (4.0 mL). Isolated yields. c The yield was determined by 19F NMR spectroscopy with PhOCF3 as internal standard. b

b

3. Conclusions In conclusion, we have developed the method for the synthesis of propargylic and allylic trifluoromethyl selenoethers via the copper-mediated trifluoromethylselenolation of propargylic chlorides and allylic bromides. A variety of propargylic and allylic trifluoromethyl selenoethers can be obtained in moderate to good

M. Rong et al. / Tetrahedron 70 (2014) 8872e8878

yields. A purely free radical pathway is not involved in the present reaction. The scope of the reaction and potential synthetic applications of the copper-mediated trifluoromethylselenolation are currently under investigation. 4. Experimental 4.1. General experimental H NMR, 19F NMR, and 13C NMR spectra were recorded using Bruker AVIII 400 spectrometer. 1H NMR and 13C NMR chemical shifts were reported in parts per million (ppm) downfield from tetramethylsilane and 19F NMR chemical shifts were determined relative to CFCl3 as the external standard and low field is positive. Coupling constants (J) are reported in hertz (Hz). The residual solvent peak was used as an internal reference: 1H NMR (chloroform d 7.26) and 13C NMR (chloroform d 77.0). The following abbreviations were used to explain the multiplicities: s¼singlet, d¼doublet, t¼triplet, q¼quartet, m¼multiplet, br¼broad. HRMS were obtained on Waters GCT-TOF at the Shanghai Institute of Organic Chemistry. Propargylic chlorides 2,23 allylic bromides 4,29 and [(bpy) Cu(SeCF3)]217 were prepared according to the published procedures. Other reagents were received from commercial sources. Solvents were freshly dried and degassed according to the purification handbook Purification of Laboratory Chemicals prior to use. Column chromatography purifications were performed by flash chromatography using Merck silica gel 60.

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as a pale yellow oil in 75% yield (83 mg). Rf (pentane): 0.78. 1H NMR (400 MHz, CDCl3) d 7.32e7.22 (m, 3H), 7.19 (d, J¼7.3 Hz, 1H), 3.94 (s, 2H), 2.38 (s, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 138.1 (s), 132.3 (s), 129.5 (s), 128.8 (s), 128.2 (s), 122.6 (q, J¼331.7 Hz), 122.3 (s), 85.2 (s), 83.0 (s), 21.2 (s), 11.7 (q, J¼2.5 Hz). IR (KBr) n 2926, 2857, 1486, 1203, 1135, 1098, 1073, 784, 739, 690 cm1. GCeMS m/z 277 (MþH), 129 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C11H19F74 3 Se: 271.9881; found: 271.9883.

1

4.2. General procedure for trifluoromethylselenolation of propargylic chlorides with [(bpy)Cu(SeCF3)]2 (1) Propargylic chlorides (2) (0.40 mmol), [(bpy)Cu(SeCF3)]2 (1) (177 mg, 0.24 mmol), and DMF (4.0 mL) were added to a reaction tube equipped with a stir bar. The mixture was stirred at 70  C for 16 h. The reaction mixture was filtered through a pad of Celite. The filtrate was added water (310 mL) at 0  C. The resulting mixture was extracted with Et2O (315 mL), and the combined organic layers were washed with water, and then dried over MgSO4. The solvent was removed by rotary evaporation in an ice bath and the resulting product was purified by flash chromatography on silica gel using pentane for elution. 4.2.1. (3-Phenylprop-2-ynyl)(trifluoromethyl)selane (3a). Following the general procedure and workup, 3a was isolated as a pale yellow oil in 83% yield (87 mg). Rf (pentane): 0.71. 1H NMR (400 MHz, CDCl3) d 7.50e7.42 (m, 2H), 7.37e7.29 (m, 3H), 3.94 (s, 2H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 131.8 (s), 128.6 (s), 128.3 (s), 122.4 (q, J¼331.7 Hz), 122.5 (s), 84.9 (s), 83.4 (s), 11.6 (q, J¼2.6 Hz). IR (KBr) n 1491, 1443, 1202, 1097, 1072, 1030, 756, 739, 690, 528 cm1. GCeMS m/z 263 (MþH), 115 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C10H7F74 3 Se: 257.9725; found: 257.9724. 4.2.2. (3-p-Tolylprop-2-ynyl)(trifluoromethyl)selane (3b). Following the general procedure and workup, 3b was isolated as a pale yellow oil in 56% yield (62 mg). Rf (pentane): 0.73. 1H NMR (400 MHz, CDCl3) d 7.35 (d, J¼7.7 Hz, 2H), 7.15 (d, J¼7.7 Hz, 2H), 3.93 (s, 2H), 2.38 (s, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 138.8 (s), 131.6 (s), 129.1 (s), 122.6 (q, J¼331.6 Hz), 119.4 (s), 85.1 (s), 82.6 (s), 21.4 (s), 11.7 (q, J¼2.5 Hz). IR (KBr) n 2925, 1510, 1275, 1202, 1181, 1097, 1072, 816, 739, 528 cm1. GCeMS m/z 277 (MþH), 129 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C11H9F74 3 Se: 271.9881; found: 271.9878. 4 . 2 . 3 . ( 3 - m -T o l y l p r o p - 2 - y n y l ) ( t r i fl u o r o m e t h y l ) s e l a n e (3c). Following the general procedure and workup, 3c was isolated

4.2.4. (3-(4-Ethylphenyl)prop-2-ynyl)(trifluoromethyl)selane (3d). Yield 80% (19F NMR). Following the general procedure and workup, 3d was isolated as a pale yellow oil in 71% yield (90 mg). Rf (pentane): 0.62. 1H NMR (400 MHz, CDCl3) d 7.38 (d, J¼8.0 Hz, 2H), 7.18 (d, J¼8.0 Hz, 2H), 3.94 (s, 2H), 2.68 (q, J¼7.6 Hz, 2H), 1.26 (t, J¼7.6 Hz, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 145.1 (s), 131.7 (s), 127.9 (s), 122.6 (q, J¼331.7 Hz), 119.6 (s), 85.1 (s), 82.6 (s), 28.8 (s), 15.4 (s), 11.8 (q, J¼2.6 Hz). IR (KBr) n 2967, 2930, 2873, 1511, 1459, 1201, 1098, 1072, 833, 739 cm1. GCeMS m/z 291 (MþH), 143 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C12H11F74 3 Se: 286.0038; found: 286.0036. 4.2.5. (3-(4-Propylphenyl)prop-2-nyl)(trifluoromethyl)selane (3e). Yield 66% (19F NMR). Following the general procedure and workup, 3e was isolated as a pale yellow oil in 54% yield (75 mg). Rf (pentane): 0.70. 1H NMR (400 MHz, CDCl3) d 7.36 (d, J¼8.1 Hz, 2H), 7.14 (d, J¼8.1 Hz, 2H), 3.93 (s, 2H), 2.60 (t, J¼7.4 Hz, 2H), 1.65 (dq, J¼14.8, 7.4 Hz, 2H), 0.95 (t, J¼7.4 Hz, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 143.6 (s), 131.6 (s), 128.5 (s), 122.6 (q, J¼331.7 Hz), 119.7 (s), 85.2 (s), 82.6 (s), 38.0 (s), 24.4 (s), 13.7 (s), 11.8 (q, J¼2.6 Hz). IR (KBr) n 2959, 2929, 2872, 1511, 1201, 1137, 1099, 1072, 841, 739 cm1. GCeMS m/z 305 (MþH), 157 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C13H13F74 3 Se: 300.0194; found: 300.0191. 4.2.6. (3-(4-Butylphenyl)prop-2-ynyl)(trifluoromethyl)selane (3f). Following the general procedure and workup, 3f was isolated as a pale yellow oil in 67% yield (85 mg). Rf (pentane): 0.70. 1H NMR (400 MHz, CDCl3) d 7.36 (d, J¼8.1 Hz, 2H), 7.15 (d, J¼8.1 Hz, 2H), 3.93 (s, 2H), 2.63 (t, J¼7.4 Hz, 2H), 1.69e1.54 (m, 2H), 1.37 (td, J¼14.7, 7.4 Hz, 2H), 0.95 (t, J¼7.3 Hz, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 143.8 (s), 131.6 (s), 128.4 (s), 122.6 (q, J¼331.7 Hz), 119.6 (s), 85.1 (s), 82.6 (s), 35.6 (s), 33.4 (s), 22.3 (s), 13.9 (s), 11.8 (q, 2.5 Hz). IR (KBr) n 2928, 1200, 1136, 1098, 1072, 911, 834, 739, 604, 545 cm1. GCeMS m/z 319 (MþH), 171 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C14H15F74 3 Se: 314.0351; found: 314.0353. 4.2.7. (3-(4-tert-Butylphenyl)prop-2-ynyl)(trifluoromethyl)selane (3g). Yield 68% (19F NMR). Following the general procedure and workup, 3g was isolated as a pale yellow oil in 59% yield (60 mg). Rf (pentane): 0.48. 1H NMR (400 MHz, CDCl3) d 7.43e7.33 (m, 4H), 3.94 (s, 2H), 1.35 (s, 9H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 151.9 (s), 131.5 (s), 125.3 (s), 122.6 (q, J¼331.8 Hz), 119.5 (s), 85.1 (s), 82.6 (s), 34.8 (s), 31.1 (s), 11.8 (q, J¼2.6 Hz). IR (KBr) n 2963, 2927, 2870, 1202, 1138, 1098, 1073, 839, 739, 562 cm1. GCeMS m/z 319 (MþH), 171 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C14H15F74 3 Se: 314.0351; found: 314.0356. 4.2.8. (3-(4-Pentylphenyl)prop-2-ynyl)(trifluoromethyl)selane (3h). Following the general procedure and workup, 3h was isolated as a pale yellow oil in 70% yield (93 mg). Rf (pentane): 0.75. 1H NMR (400 MHz, CDCl3) d 7.38 (d, J¼8.0 Hz, 2H), 7.17 (d, J¼8.0 Hz, 2H), 3.94 (s, 2H), 2.64 (t, J¼7.2 Hz, 2H), 1.69e1.61 (m, 2H), 1.38e1.36 (m, 4H), 0.95 (t, J¼6.9 Hz, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C

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NMR (101 MHz, CDCl3) d 143.8 (s), 131.7 (s), 128.0 (s), 122.6 (q, J¼332.1 Hz), 119.6 (s), 85.2 (s), 82.6 (s), 35.9 (s), 31.4 (s), 30.9 (s), 22.5 (s), 14.0 (s), 11.8 (q, J¼1.9 Hz). IR (KBr) n 2957, 2928, 2857, 1511, 1464, 1200, 1138, 1099, 1072, 739 cm1. GCeMS m/z 333 (MþH), 185 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C15H17F74 3 Se: 328.0507; found: 328.0510. 4.2.9. (Trifluoromethyl)(3-(2-(trifluoromethyl)phenyl)prop-2-ynyl) selane (3i). Following the general procedure and workup, 3i was isolated as a pale yellow oil in 47% yield (62 mg). Rf (pentane): 0.41. 1H NMR (400 MHz, CDCl3) d 7.68 (d, J¼7.5 Hz, 1H), 7.59 (d, J¼7.5 Hz, 1H), 7.51 (t, J¼7.5 Hz, 1H), 7.44 (t, J¼7.5 Hz, 1H), 3.95 (s, 2H). 19F NMR (376 MHz, CDCl3) d 34.7 (s, 3F), 62.4 (s, 3F).13C NMR (101 MHz, CDCl3) d 134.2 (s), 131.4 (q, J¼1.1 Hz), 128.4 (s), 125.8 (q, J¼5.1 Hz), 123.4 (q, J¼273.3 Hz), 122.4 (q, J¼331.6 Hz), 120.7 (q, J¼2.2 Hz), 89.2 (q, J¼1.0 Hz), 80.7 (s), 29.7 (s), 11.3 (q, J¼2.6 Hz). IR (KBr) n 2926, 2855, 1320, 1173, 1140, 1099, 1073, 1063, 1034, 765 cm1. GCeMS m/z 331 (MþH), 183 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C11H16F74 6 Se: 325.9598; found: 325.9600. 4.2.10. (3-(4-Methoxyphenyl)prop-2-ynyl)(trifluoromethyl)selane (3j). Following the general procedure and workup, 3j was isolated as a pale yellow oil in 53% yield (74 mg). Rf (pentane): 0.80. 1H NMR (400 MHz, CDCl3) d 7.38 (d, J¼8.8 Hz, 2H), 6.86 (d, J¼8.8 Hz, 2H), 3.93 (s, 2H), 3.83 (s, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13 C NMR (101 MHz, CDCl3) d 159.8 (s), 133.2 (s), 122.6 (q, J¼331.7 Hz), 114.5 (s), 114.0 (s), 84.9 (s), 81.9 (s), 55.3 (s), 11.9 (q, J¼2.6 Hz). IR (KBr) n 2955, 2925, 2854, 1607, 1510, 1249, 1173, 1137, 1099, 832 cm1. GCeMS m/z 293 (MþH), 145 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C11H9F3O74Se: 287.9830; found: 287.9831. 4.2.11. (3-(4-(Pentyloxy)phenyl)prop-2-ynyl)(trifluoromethyl)selane (3k). Following the general procedure and workup, 3k was isolated as a pale yellow oil in 59% yield (82 mg). Rf (pentane): 0.39. 1H NMR (400 MHz, CDCl3) d 7.37 (d, J¼8.7 Hz, 2H), 6.85 (d, J¼8.7 Hz, 2H), 3.97 (t, J¼6.6 Hz, 2H), 3.93 (s, 2H), 1.86e1.76 (m, 2H), 1.50e1.37 (m, 4H), 0.97 (t, J¼7.0 Hz, 3H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13 C NMR (101 MHz, CDCl3) d 159.5 (s), 133.2 (s), 122.6 (q, J¼331.7 Hz), 114.5 (s), 114.3 (s), 85.1 (s), 81.8 (s), 68.1 (s), 28.9 (s), 28.2 (s), 22.4 (s), 14.0 (s), 11.9 (q, J¼2.6 Hz). IR (KBr) n 2957, 2931, 1607, 1510, 1291, 1250, 1173, 1098, 1072, 831 cm1. GCeMS m/z 349 (MþH), 201 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C15H17F3O74Se: 344.0456; found: 344.0459. 4.2.12. (3-(4-Fluorophenyl)prop-2-ynyl)(trifluoromethyl)selane (3l). Following the general procedure and workup, 3l was isolated as a pale yellow oil in 48% yield (54 mg). Rf (pentane): 0.84. 1H NMR (400 MHz, CDCl3) d 7.59e7.24 (m, 2H), 7.05e7.01 (m, 2H), 3.91 (s, 2H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F), 110.3 (s, 1F). 13C NMR (101 MHz, CDCl3) d 162.7 (d, J¼249.9 Hz), 133.7 (d, J¼8.4 Hz), 122.5 (q, J¼331.7 Hz), 118.6 (d, J¼3.6 Hz), 115.6 (d, J¼22.1 Hz), 83.8 (s), 83.2 (s), 11.4 (q, J¼2.5 Hz). IR (KBr) n 1602, 1508, 1233, 1132, 1098, 1072, 815, 836, 739, 530 cm1. GCeMS m/z 281 (MþH), 133 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C10H6F74 4 Se: 275.9630; found: 275.9629. 4.2.13. (3-(4-Chlorophenyl)prop-2-ynyl)(trifluoromethyl)selane (3m). Following the general procedure and workup, 3m was isolated as a pale yellow oil in 68% yield (81 mg). Rf (pentane): 0.90. 1H NMR (400 MHz, CDCl3) d 7.37 (d, J¼8.3 Hz, 2H), 7.31 (d, J¼8.3 Hz, 2H), 3.91 (s, 2H). 19F NMR (376 MHz, CDCl3) d 34.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 134.7 (s), 133.0 (s), 128.7 (s), 122.5 (q, J¼331.8 Hz), 121.0 (s), 84.5 (s), 83.8 (s), 11.4 (q, J¼2.5 Hz). IR (KBr) n 1490, 1276, 1201, 1095, 1071, 1015, 828, 751, 739, 525 cm1. GCeMS

m/z 297 (MþH), 149 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C10H6ClF74 3 Se: 291.9335; found: 291.9333. 4.3. General procedure for trifluoromethylselenolation of allylic bromides with [(bpy)Cu(SeCF3)]2 (1) Allylic bromides (4) (0.40 mmol), [(bpy)Cu(SeCF3)]2 (1) (177 mg, 0.24 mmol), and DMF (4.0 mL) were added to a reaction tube equipped with a stir bar. The mixture was stirred at 70  C for 16 h. The reaction mixture was filtered through a pad of Celite. To the filtrate was added water (315 mL) at 0  C. The resulting mixture was extracted with Et2O (315 mL), and the combined organic layers was washed with water, and then dried over MgSO4. The solvent was removed by rotary evaporation in an ice bath and the resulting product was purified by column chromatography on silica gel using pentane for elution. 4.3.1. Cinnamyl(trifluoromethyl)selane (5a). Following the general procedure and workup, 5a was isolated as a colorless oil in 82% yield (87 mg). Rf (pentane): 0.82. 1H NMR (400 MHz, CDCl3) d 7.43e7.29 (m, 5H), 6.62 (d, J¼15.6 Hz, 1H), 6.42e6.34 (m, 1H), 3.88 (d, J¼7.8 Hz, 2H). 19F NMR (376 MHz, CDCl3) d 33.8 (s, 3F). 13C NMR (101 MHz, CDCl3) d 136.2 (s), 134.0 (s), 128.7 (s), 128.1 (s), 126.5 (s), 124.0 (s), 122.8 (q, J¼331.4 Hz), 27.9 (q, J¼1.7 Hz). IR (KBr) n 3061, 3030, 1497, 1202, 1097, 1072, 962, 747, 739, 693 cm1. GCeMS m/z 265 (MþH), 117 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C10H9F74 3 Se: 259.9881; found: 259.9877. 4.3.2. (E)-(3-p-Tolylallyl)(trifluoromethyl)selane (5b). Following the general procedure and workup, 5b was isolated as a colorless oil in 70% yield (78 mg). Rf (pentane): 0.77. 1H NMR (400 MHz, CDCl3) d 7.31 (d, J¼7.4 Hz, 2H), 7.18 (d, J¼7.4 Hz, 2H), 6.59 (d, J¼15.6 Hz, 1H), 6.37e6.25 (m, 1H), 3.88 (d, J¼7.7 Hz, 2H), 2.39 (s, 3H). 19F NMR (376 MHz, CDCl3) d 33.8 (s, 3F). 13C NMR (101 MHz, CDCl3) d 138.0 (s), 134.0 (s), 133.4 (s), 129.4 (s), 126.4 (s), 122.9 (s), 122.8 (q, J¼331.4 Hz), 28.1 (q, J¼1.7 Hz), 21.2 (s). IR (KBr) n 2925, 2858, 1513, 1202, 1097, 1071, 963, 796, 738, 499 cm1. GCeMS m/z 279 (MþH), 131 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C11H11F74 3 Se: 274.0038; found: 274.0042. 4.3.3. (E)-(3-Mesitylallyl)(trifluoromethyl)selane (5c). Following the general procedure and workup, 5c was isolated as a pale yellow oil in 61% yield (75 mg). Rf (pentane): 0.68. 1H NMR (400 MHz, CDCl3) d 6.95 (s, 2H), 6.65 (d, J¼15.9 Hz, 1H), 5.98e5.90 (m, 1H), 3.92 (d, J¼7.7 Hz, 2H), 2.36 (s, 3H), 2.35 (s, 6H). 19F NMR (376 MHz, CDCl3) d 33.7 (s, 3F). 13C NMR (101 MHz, CDCl3) d 136.7 (s), 136.1 (s), 132.8 (s), 131.8 (s), 129.2 (s), 128.8 (s), 122.8 (q, J¼331.2 Hz), 28.3 (q, J¼1.7 Hz), 21.0 (s), 20.8 (s). IR (KBr) n 2923, 2859, 1480, 1456, 1202, 1098, 1073, 970, 853, 738 cm1. GCeMS m/z 307 (MþH), 159 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C13H15F74 3 Se: 302.0351; found: 302.0352. 4.3.4. (E)-(3-(4-Isopropylphenyl)allyl)(trifluoromethyl)selane (5d). Following the general procedure and workup, 5d was isolated as a colorless oil in 56% yield (69 mg). Rf (pentane): 0.82. 1H NMR (400 MHz, CDCl3) d 7.35 (d, J¼7.4 Hz, 2H), 7.24 (d, J¼7.4 Hz, 2H), 6.60 (d, J¼15.6 Hz, 1H), 6.41e6.25 (m, 1H), 3.88 (d, J¼7.6 Hz, 2H), 2.95 (dt, J¼13.6, 6.8 Hz, 1H), 1.30 (d, J¼7.3 Hz, 6H). 19F NMR (376 MHz, CDCl3) d 33.8 (s, 3F). 13C NMR (101 MHz, CDCl3) d 149.0 (s), 134.0 (s), 133.9 (s), 126.7 (s), 126.5 (s), 122.9 (s), 122.8 (q, J¼331.2 Hz), 33.9 (s), 28.1 (q, J¼1.6 Hz), 23.9 (s). IR (KBr) n 2961, 2928, 2871, 1512, 1201, 1098, 1074, 963, 821, 738 cm1. GCeMS m/z 307 (MþH), 159 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C13H15F74 3 Se: 302.0351; found: 302.0353. 4.3.5. (E)-(3-(4-tert-Butylphenyl)allyl)(trifluoromethyl)selane (5e). Following the general procedure and workup, 5e was isolated

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as a colorless oil in 79% yield (101 mg). Rf (pentane): 0.60. 1H NMR (400 MHz, CDCl3) d 7.42 (d, J¼8.5 Hz, 2H), 7.37 (d, J¼8.5 Hz, 2H), 6.62 (d, J¼15.6 Hz, 1H), 6.39e6.31 (m, 1H), 3.89 (d, J¼7.8 Hz, 2H), 1.38 (s, 9H). 19F NMR (376 MHz, CDCl3) d 33.7 (s, 3F). 13C NMR (101 MHz, CDCl3) d 151.3 (s), 133.9 (s), 133.5 (s), 126.3 (s), 125.6 (s), 123.1 (s), 122.8 (q, J¼331.3 Hz), 34.6 (s), 31.3 (s), 28.1 (q, J¼1.7 Hz). IR (KBr) n 2964, 2869, 1514, 1364, 1269, 1202, 1098, 964, 820, 738 cm1. GCeMS m/z 321 (MþH), 173 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C14H17F74 3 Se: 316.0507; found: 316.0506. 4.3.6. (E)-Methyl(4-(3-(trifluoromethylselanyl)prop-1-enyl)phenyl) sulfane (5f). Following the general procedure and workup, 5f was isolated as a white powder in 71% yield (88 mg). Mp: 40e41  C. Rf (pentane): 0.38. 1H NMR (400 MHz, CDCl3) d 7.31 (d, J¼8.4 Hz, 2H), 7.23 (d, J¼8.4 Hz, 2H), 6.55 (d, J¼15.6 Hz, 1H), 6.35e6.27 (m, 1H), 3.86 (d, J¼7.8 Hz, 2H), 2.51 (s, 3H). 19F NMR (376 MHz, CDCl3) d 33.7 (s, 3F). 13C NMR (101 MHz, CDCl3) d 138.5 (s), 133.4 (s), 133.1 (s), 126.9 (s), 126.6 (s), 123.3 (s), 122.8 (q, J¼331.3 Hz), 28.1 (q, J¼1.7 Hz), 15.7 (s). IR (KBr) n 2921, 1493, 1203, 1092, 1069, 965, 813, 787, 737 cm1. GCeMS m/z 311 (MþH), 163 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C11H11F3S74Se: 305.9758; found: 305.9754. 4.3.7. (E)-(Trifluoromethyl)(3-(4-(trifluoromethyl)phenyl)allyl)selane (5g). Following the general procedure and workup, 5g was isolated as a colorless oil in 41% yield (55 mg). Rf (pentane): 0.45. 1H NMR (400 MHz, CDCl3) d 7.61 (d, J¼8.2 Hz, 2H), 7.49 (d, J¼8.2 Hz, 2H), 6.63 (d, J¼15.7 Hz, 1H), 6.51e6.43 (m, 1H), 3.86 (d, J¼7.7 Hz, 2H). 19F NMR (376 MHz, CDCl3) d 33.7 (s, 3F), 62.6 (s, 3F). 13C NMR (101 MHz, CDCl3) d 139.6 (q, J¼1.4 Hz), 132.4 (s), 127.0 (s), 126.6 (s), 125.6 (q, J¼3.9 Hz), d 124.1 (q, J¼271.9 Hz), 125.4 (s), 122.6 (q, J¼331.3 Hz), 27.5 (q, J¼1.7 Hz). IR (KBr) n 2928, 1616, 1327, 1202, 1098, 1069, 1017, 965, 826, 739 cm1. GCeMS m/z 333 (MþH), 185 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C11H8F74 6 Se: 327.9755; found: 327.9751. 4.3.8. Cyclohex-2-enyl(trifluoromethyl)selane (5h). 19F NMR analysis of the filtrate indicated that 5h was produced in 91% yield. Following the general procedure and workup, 5h was isolated as a colorless oil in 65% yield (60 mg). Rf (pentane): 0.88. 1H NMR (400 MHz, CDCl3) d 5.93e5.79 (m, 2H), 4.27 (s, 1H), 2.18e2.07 (m, 4H), 1.88e1.71 (m, 2H). 19F NMR (376 MHz, CDCl3) d 33.5 (s, 3F). 13 C NMR (101 MHz, CDCl3) d 132.0 (s), 126.2 (q, J¼304.5 Hz), 125.6 (s), 40.6 (s), 30.1 (s), 24.6 (s), 19.2 (s). IR (KBr) n 2926, 2856, 1459, 1190, 1101, 736 cm1. GCeMS m/z 229 (MþH), 81 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C7H9F74 3 Se: 223.9881; found: 223.9876. 4.3.9. (3,7-Dimethylocta-2,6-dienyl)(trifluoromethyl)selane (5i). Following the general procedure and workup, 5i was isolated as a colorless oil in 62% yield (71 mg, E/Z ratio¼6:1). E-isomer 5i: spectral parameters for the E isomer were obtained on an enriched chromatographic fraction still containing the Z-isomer. Rf (pentane): 0.41. 1H NMR (400 MHz, CDCl3) d 5.40 (t, J¼8.2 Hz, 1H), 5.09 (t, J¼6.1 Hz, 1H), 3.72 (d, J¼8.3 Hz, 2H), 2.17e2.05 (m, 4H), 1.72 (s, 3H), 1.71 (s, 3H), 1.63 (s, 3H). 19F NMR (376 MHz, CDCl3) d 34.0 (s, 3F). 13C NMR (101 MHz, CDCl3) d 141.8 (s), 131.9 (s), 123.6 (s), 122.9 (q, J¼331.2 Hz), 117.9 (s), 39.6 (s), 26.3 (s), 25.6 (s), 23.5 (q, J¼3.3 Hz), 17.7 (s), 15.8 (s). IR (KBr) n 2926, 2857, 1455, 1378, 1199, 1099, 738 cm1. GCeMS m/z 285 (MþH), 137 (MþSeCF3 100%). HRMS (EI) m/z: calculated for [C11H17F74 3 SeCF3]: 211.0555; found: 211.0551. 4.3.10. (Z)-Ethyl 3-ethoxy-4-(trifluoromethylselanyl)but-2-enoate (5j). Following the general procedure and workup, 5j was isolated as a colorless oil in 64% yield (78 mg). Rf (pentane): 0.52. 1H

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NMR (400 MHz, CDCl3) d 5.07 (s, 1H), 4.17 (q, J¼7.1 Hz, 2H), 4.12 (s, 2H), 3.90 (q, J¼7.0 Hz, 2H), 1.37 (t, J¼7.0 Hz, 3H), 1.29 (t, J¼7.1 Hz, 3H). 19F NMR (376 MHz, CDCl3) d 34.9 (s, 3F). 13C NMR (101 MHz, CDCl3) d 171.3 (s), 167.5 (s), 122.9 (q, J¼331.2 Hz), 91.8 (s), 64.8 (s), 59.9 (s), 24.3 (q, J¼1.7 Hz), 14.3 (s), 13.8 (s). IR (KBr) n 2985, 2933, 1698, 1619, 1373, 1349, 1301, 1133, 1101, 1053 cm1. GCeMS m/z 305 (MþH), 157 (MþSeCF3 100%). HRMS (EI) m/z: calculated for C9H13F3O74 3 Se: 300.0042; found: 300.0046. 4.4. Procedure for the reaction of 1 with (3-chloroprop-1ynyl)benzene (2a) in the presence of 1.0 equiv CHD Compound 1 (44.1 mg, 0.060 mmol), compound 2a (15.0 mg, 0.10 mmol), CHD (9.5 mg, 0.10 mmol, 1.0 equiv), and 1.5 mL DMF were added to an oven-dried 5 mL test tube with Teflon screw cap. The tube was sealed and the reaction solution was placed into a preheated 70  C oil bath for 16 h. The tube was removed from the oil bath and cooled to room temperature, and then 10 mL (trifluoromethoxy)benzene was added as an internal standard. The resulting mixture was filtered through a layer of Celite. The filtrate was analyzed by 19F NMR and GCeMS. The yield of the (3phenylprop-2-ynyl)(trifluoromethyl)selane (3a) was calculated to be 82%. 4.5. Procedure for the reaction of 1 with (3-chloroprop-1ynyl)benzene (2a) in the presence of 1.0 equiv TEMPO Compound 1 (44.1 mg, 0.060 mmol), Compound 2a (15.0 mg, 0.10 mmol), TEMPO (15.6 mg, 0.10 mmol, 1.0 equiv), and 1.5 mL DMF were added to an oven-dried 5 mL test tube with Teflon screw cap. The tube was sealed and the reaction solution was placed into a preheated 70  C oil bath for 16 h. The tube was removed from the oil bath and cooled to room temperature, and then 10 mL (trifluoromethoxy)benzene was added as an internal standard. The resulting mixture was filtered through a layer of Celite. The filtrate was analyzed by 19F NMR and GCeMS. The yield of the (3phenylprop-2-ynyl)(trifluoromethyl)selane (3a) was calculated to be 39%. Acknowledgements Financial support from National Natural Science Foundation of China (21072030, 21372044), Research Fund for the Doctoral Program of Higher Education of China (No. 20123514110003), the SRF for ROCS, SEM, China (2012-1707), the Science Foundation of the Fujian Province, China (2013J01040), and Fuzhou University (022318, 022494) is gratefully acknowledged. Supplementary data Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.tet.2014.09.091. References and notes 1. (a) Filler, R.; Kobayashi, Y.; Yugapolskii, L. M. Organofluorine Compounds in Medicinal Chemistry and Biomedical Applications; Elsevier: Amsterdam, The Netherlands, 1993; (b) Yamazaki, T.; Taguchi, T.; Ojima, I. Fluorine in Medicinal Chemistry and Chemical Biology; WileyeBlackwell: Chichester, UK, 2009. € ller, K.; Faeh, C.; Diederich, F. Science 2007, 317, 1881e1886; (b) Purser, S.; 2. (a) Mu Moore, P. R.; Swallow, S.; Gouverneur, V. Chem. Soc. Rev. 2008, 37, 320e330; (c) Hagmann, W. K. J. Med. Chem. 2008, 51, 4359e4369; (d) Manteau, B.; Pazenok, S.; Vors, J.-P.; Leroux, F. R. J. Fluorine Chem. 2010, 131, 140e158; (e) Furuya, T.; Kamlet, A. S.; Ritter, T. Nature 2011, 473, 470e477; (f) Liu, T.; Shen, Q. Eur. J. Org. Chem. 2012, 2012, 6679e6687. 3. Becker, A. Inventory of Industrial Fluoro-biochemicals; Eyrolles: Paris, France, 1996.

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