Copper-Catalyzed Semihydrogenation of Alkynes to Z-Alkenes

Abstract

Copper-catalyzed semihydrogenation of internal alkynes has been developed. The reaction proceeds under an atmosphere of hydrogen (5 atm) at 100 °C in the presence of a readily available [(PPh₃)CuCl]₄ catalyst to give various Z-alkenes stereoselectively.

Key words

alkynes - alkenes - catalysis - copper - hydrogenation

• References and Notes

• 1a For reviews on copper-catalyzed reduction of carbonyl compounds and Michael acceptors, see: Rendler S, Oestreich M. Angew. Chem. Int. Ed. 2007; 46: 498 ; and references cited therein
• 1b Díez-González S, Nolan SP. Acc. Chem. Res. 2008; 41: 349 ; and references cited therein
• 1c Deutsch C, Krause N, Lipshutz BH. Chem. Rev. 2008; 108: 2916 ; and references cited therein
• 1d Lipshutz BH. Synlett 2009; 509 ; and references cited therein

For references on copper-catalyzed semireduction of alkynes, see:
• 2a Semba K, Fujihara T, Xu T, Terao J, Tsuji Y. Adv. Synth. Catal. 2012; 354: 1542
• 2b Whittaker AM, Lalic G. Org. Lett. 2013; 15: 1112
• 2c Wang G.-H, Bin H.-Y, Sun M, Chen S.-W, Liu J.-H, Zhong C.-M. Tetrahedron 2014; 70: 2175
• 2d Cao H, Chen T, Zhou Y, Han D, Yin S.-F, Han L.-B. Adv. Synth. Catal. 2014; 356: 765

For the semireduction of alkynes using a stoichiometric amount of [(PPh₃)CuH]₆, see:
• 2e Daeuble JF, Mcgettigan C, Stryker JM. Tetrahedron Lett. 1990; 31: 2397
• 3a Mahoney WS, Stryker JM. J. Am. Chem. Soc. 1989; 111: 8818
• 3b Chen J.-X, Daeuble JF, Brestensky DM, Stryker JM. Tetrahedron 2000; 56: 2153
• 3c Chen J.-X, Daeuble JF. Tetrahedron 2000; 56: 2789
• 3d Shimizu H, Igarashi D, Kuriyama W, Yusa Y, Sayo N, Saito T. Org. Lett. 2007; 9: 1655
• 3e Junge K, Wendt B, Addis D, Zhou S, Das S, Fleischer S, Beller M. Chem. Eur. J. 2011; 17: 101
• 4 Sokol’skii DV, Ualikhanova A. Russ. J. Phys. Chem. 1977; 51: 886
• 5a Brown CA, Ahuja VK. J. Org. Chem. 1973; 38: 2226
• 5b Brunet J.-J, Gallois P, Caubere P. J. Org. Chem. 1980; 45: 1937
• 5c Brunet J.-J, Caubere P. J. Org. Chem. 1984; 49: 4058
• 5d Choudary BM, Sharma GV. M, Bharathi P. Angew. Chem., Int. Ed. Engl. 1989; 28: 465
• 5e Choi J, Yoon NM. Tetrahedron Lett. 1996; 37: 1057
• 5f Alonso F, Osante I, Yus M. Tetrahedron 2007; 63: 93
• 5g Mizugaki T, Murata M, Fukubayashi S, Mitsudome T, Jitsukawa K, Kaneda K. Chem. Commun. 2008; 241
• 6a Lindlar H. Helv. Chim. Acta 1952; 35: 446
• 6b Lindlar H, Dubuis R. Org. Synth. 1966; 46: 89
• 6c Marvell EN, Li T. Synthesis 1973; 457
• 6d Rajaram J, Narula AP. S, Chawla HP. S, Dev S. Tetrahedron 1983; 39: 2315
• 7a Schrock RR, Osborn JA. J. Am. Chem. Soc. 1976; 98: 2143
• 7b Sodeoka M, Shibasaki M. J. Org. Chem. 1985; 50: 1149
• 7c van Laren MW, Elsevier CJ. Angew. Chem. Int. Ed. 1999; 38: 3715
• 7d Sprengers JW, Wassenaar J, Clement ND, Cavell KJ, Elsevier CJ. Angew. Chem. Int. Ed. 2005; 44: 2026
• 7e Belger C, Neisius NM, Plietker B. Chem. Eur. J. 2010; 16: 12214
• 7f La Pierre HS, Arnold J, Toste FD. Angew. Chem. Int. Ed. 2011; 50: 3900
• 7g Gianetti TL, Tomson NC, Arnold J, Bergman RG. J. Am. Chem. Soc. 2011; 133: 14904
• 7h Chernichenko K, Madarász Á, Pápai I, Nieger M, Leskelä M, Repo T. Nat. Chem. 2013; 5: 718

Transfer semihydrogenation of alkynes was also reported, see:
• 7i Trost BM, Braslau R. Tetrahedron Lett. 1989; 30: 4657
• 7j Hauwert P, Maestri G, Sprengers JW, Catellani M, Elsevier CJ. Angew. Chem. Int. Ed. 2008; 47: 3223
• 7k Hauwert P, Boerleider R, Warsink S, Weigand JJ, Elsevier CJ. J. Am. Chem. Soc. 2010; 132: 16900
• 7l Hua JL. R, Liu T. J. Org. Chem. 2010; 75: 2966
• 7m Hua JL. R. Chem. Eur. J. 2011; 17: 8462
• 7n Shen R, Chen T, Zhao Y, Qiu R, Zhou Y, Yin S, Wang X, Goto M, Han L.-B. J. Am. Chem. Soc. 2011; 133: 17037
• 8 Churchill MR, Kalra K. Inorg. Chem. 1974; 13: 1065
• 9 General Procedure for the Copper-Catalyzed Semihydro­genationIn a glove box, [(PPh₃)CuCl]₄ (7.2 mg, 5.0 μmol), toluene (1.0 mL), LiOt-Bu (40 mg, 0.50 mmol), and i-PrOH (60 mg, 1.0 mmol) were added to a vial in this order. After being stirred for 1 min at r.t., alkyne 1 (1.0 mmol) and toluene (2.0 mL) were added to the resulting mixture. The vial was placed in an autoclave, and the autoclave was taken out of the glove box. An N₂ atmosphere in the autoclave was purged by positive pressure of H₂. Then, the mixture was stirred at 100 °C for 3 h under H₂ (5 atm). After being cooled to r.t., H₂ was released, and the mixture was diluted with EtOAc. The conversion of alkynes was determined by GC analysis with n-tridecane as an internal standard. The resulting solution was filtered through a pad of silica gel, and the filtrate was concentrated. The residue was purified by medium-pressure column chromatography on silica gel to give (Z)-2.Representative data:(Z)-2d: The reaction of 1d (180 mg, 1.0 mmol) at 60 °C followed by purification by MPLC (16 g of silica gel and Biotage^® SNAP Ultra 10 g; n-hexane) gave the corresponding product (160 mg, 0.91 mmol, 91%) as a mixture of (Z)-2d,^14a (E)-2d,^14b and 3d ^14c [(Z)-2d/(E)-2d/3d = 95:5:<1 determined by ¹H NMR analysis] as a colorless oil; R_f = 0.53 (hexane). ¹H NMR (CDCl₃, 400 MHz): δ = 7.28–7.16 (m, 10 H), 6.60 (s, 2 H); ¹³C NMR (CDCl₃, 101 MHz): δ = 137.2, 130.2, 128.8, 128.2, 127.1. All the resonances of ¹H and ¹³C NMR spectra were consistent with reported values.^14a (Z)-2g: The reaction of 1g (79 mg, 0.30 mmol) at 80 °C in toluene (0.80 mL) followed by purification by MPLC (16 g of silica gel and Biotage® SNAP Ultra 10 g; n-hexane–EtOAc, 99:1 to 93:7) gave the corresponding product (Z)-2g (42 mg, 0.16 mmol, 52%) as a pale yellow oil; R_f = 0.35 (n-hexane–EtOAc, 95:5). ¹H NMR (CDCl₃, 400 MHz): δ = 7.90 (d, J = 8.5 Hz, 2 H), 7.30 (d, J = 8.5 Hz, 2 H), 7.25–7.20 (m, 5 H), 6.71 (d, J = 12.2 Hz, 1 H), 6.61 (d, J = 12.2 Hz, 1 H), 5.24 (sept, J = 6.1 Hz, 1 H), 1.36 (d, J = 6.1 Hz, 6 H); ¹³C NMR (CDCl₃, 101 MHz): δ = 165.9, 141.8, 136.7, 132.1, 129.4, 129.31, 129.28, 128.8, 128.7, 128.3, 127.4, 68.3, 21.9. HRMS–APCI (+): m/z [M + H]⁺ calcd for C₁₈H₁₉O₂: 267.1380; found: 267.1375

[(PPh₃)CuH]₆ was synthesized from Cu(Ot-Bu) and Ph₃P, see:
• 10a Goeden GV, Caulton KG. J. Am. Chem. Soc. 1981; 103: 7354

For catalytic activation of H₂ by copper salts, see
• 10b Halpern J. J. Phys. Chem. 1959; 63: 398

syn-Addition of copper hydride across internal alkynes was reported, see:
• 11a Mankad NP, Laitar DS, Sadighi JP. Organometallics 2004; 23: 3369
• 11b Fujihara T, Xu T, Semba K, Terao J, Tsuji Y. Angew. Chem. Int. Ed. 2011; 50: 523
• 12 For a reference on protonation of an alkenyl copper with an alcohol, see ref. 2a
• 13 H–D exchange between copper hydride and alcohols was reported, see ref. 2b and: Lipshutz BH, Servesko JM, Taft BR. J. Am. Chem. Soc. 2004; 126: 8352
• 14a Yan M, Jin T, Ishikawa Y, Minato T, Fujita T, Chen L.-Y, Bao M, Asao N, Chen M.-W, Yamamoto Y. J. Am. Chem. Soc. 2012; 134: 17536
• 14b Chen Z, Luo M, Wen Y, Luo G, Liu L. Org. Lett. 2014; 16: 3020
• 14c Kantam ML, Kishore R, Yadav J, Sudhakar M, Venugopal A. Adv. Synth. Catal. 2012; 354: 663