Synlett 2008(5): 691-694  
DOI: 10.1055/s-2008-1042802
LETTER
© Georg Thieme Verlag Stuttgart · New York

The First Organocatalytic Enantio- and Diastereoselective 1,3-Dipolar Cycloaddition of Azomethine Ylides with Nitroalkenes

Meng-Xia Xuea,c, Xiao-Mei Zhang*a, Liu-Zhu Gonga,b
a Key Laboratory for Asymmetric Synthesis & Chirotechnology of Sichuan Province, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, P. R. of China
Fax: +86(28)85229250; e-Mail: xmzhang@cioc.ac.cn;
b Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei, 230026, P. R. of China
c Graduate School of Chinese Academy of Sciences, Beijing, 100049, P. R. of China
Further Information

Publication History

Received 29 October 2007
Publication Date:
26 February 2008 (online)

Abstract

The first chiral thiourea-catalyzed stereoselective 1,3- dipolar cycloaddition of azomethine ylides with nitroalkenes afforded highly substituted pyrrolidines with high diastereoselectivities of up to >99:1 dr and moderate enantioselectivities.

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CCDC: 651568

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General Procedure for Asymmetric 1,3-Dipolar Cycloaddition of Azomethine YlidesA tube charged with benzophenone imines 1 (0.2 mmol), nitroalkenes 2 (0.4 mmol), catalyst 4-6 (0.02 mmol) and cyclohexane (2 mL). The mixture was stirred at 40 °C for 2 d, the solvent was removed, and the residue was analyzed by 1H NMR to determine the endo/exo ratio and purified by flash chromatography. The ee is determined by HPLC (Daicel Chirapak OD-H).

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3,5,5-Triphenyl-2-( tert -butyloxycarbonyl)-4-nitro-pyrrolidine (3a) Yield 77%; mp 110-111 °C; [α]D 20 -6.0 (c 0.2, CH2Cl2; 63% ee). 1H NMR (300 MHz, CDCl3): δ = 1.38 (s, 9 H), 3.85 (d, J = 10.5 Hz, 1 H), 4.02 (dd, J 1 = 4.2 Hz, J 2 = 4.8 Hz, 1 H), 6.07 (d, J = 4.9 Hz, 1H), 6.77-6.80 (m, 2 H), 7.18-7.46 (m, 11 H), 7.82 (d, J = 7.4 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.4, 142.7, 141.8, 137.4, 129.1, 128.7, 128.5, 127.9, 127.8, 127.7, 126.9, 125.5, 101.8, 82.2, 66.1, 59.1, 27.8 ppm. IR (KBr): ν = 3308, 2918, 2851, 1728, 1548, 1364, 1340, 1153, 837, 784, 706 cm-1. HRMS (Bio TOF Q): m/z calcd for C27H28N2O4Na+: 467.1941; found: 467.1950. The ee is 63% determined by HPLC [Daicel Chirapak OD-H, hexane-i-PrOH (95:5), flow rate 1.0 mL/min]: t R = 5.18 min, 6.17 min.

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3-( p -Methoxylphenyl)-2-( tert -butyloxycarbonyl)-4-nitro-5,5-eiphenyl-pyrrolidine (3b)
Yield 63%; mp 115-116 °C; [α]D 20 -3.4 (c 0.266, CH2Cl2; 65% ee). 1H NMR (300 MHz, CDCl3): δ = 1.37 (s, 9 H), 3.75 (d, J = 8.4 Hz, 3 H), 3.84 (s, 1 H), 3.91 (s, 1 H), 3.97 (dd, J 1 = 4.9 Hz, J 2 = 5.0 Hz, 1 H), 6.02 (d, J = 5.1 Hz, 1 H), 6.70 (s, 4 H), 7.18-7.32 (m, 4 H), 7.41 (dd, J 1 = 7.8 Hz, J 2 = 17.1 Hz, 4 H), 7.79 (d, J = 7.5 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.5, 159.0, 142.7, 141.9, 129.5, 129.1, 129.0, 128.5, 127.8, 127.6, 126.9, 125.5, 114.0, 101.9, 82.2, 66.2, 58.5, 55.2, 27.9 ppm. IR (KBr): ν = 3330, 2956, 2928, 2870, 1729, 1552, 1513, 1247, 832, 782, 712 cm-1. HRMS (Bio TOF Q): m/z calcd for C28H30N2O5Na+: 497.2047; found: 497.2036. The ee is 65% determined by HPLC [Daicel Chirapak OD-H, hexane-i-PrOH (98:2), flow rate 1.0 mL/min]: t R = 8.90 min, 10.10 min.

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3-( p -Methylphenyl)-2-( tert -butyloxycarbonyl)-4-nitro-5,5-diphenyl-pyrrolidine (3c) Yield 56%; mp 99-100 °C; [α]D 20 -7.5 (c 0.332, CH2Cl2; 62% ee). 1H NMR (300 MHz, CDCl3): δ = 1.37 (s, 9 H), 2.27 (s, 3 H), 3.83 (d, J = 9.3 Hz, 1 H), 3.99 (dd, J 1 = 4.8 Hz, J 2 = 4.8 Hz, 1 H), 6.04 (d, J = 4.8 Hz, 1 H), 6.67 (d, J = 8.1 Hz, 2 H), 6.98 (d, J = 7.8 Hz, 2 H), 7.18-7.39 (m, 6 H), 7.42-7.46 (m, 4 H), 7.81 (d, J = 1.2 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.5, 142.7, 141.9, 137.4, 134.4, 129.3, 129.0, 128.5, 127.7, 127.6, 126.9, 125.5, 101.8, 82.2, 66.1, 58.8, 27.8 ppm. IR (KBr): ν = 3454, 3311, 2971, 2925, 2866, 1728, 1547, 1448, 1365, 1339, 1152, 838, 785, 744, 705 cm-1. HRMS (Bio TOF Q): m/z calcd for C28H30N2O4Na+: 481.2098; found: 481.2088. The ee is 62% determined by HPLC [Daicel Chirapak OD-H, hexane-i-PrOH (98:2), flow rate 1.0 mL/min]: t R = 5.75 min, 6.96 min.

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3-( m -Methylphenyl)-2-( tert -butyloxycarbonyl)-4-nitro-5,5-diphenyl-pyrrolidine (3d)
Yield 68%; mp 113-114 °C; [α]D 20 +4.0 (c 0.20, CH2Cl2; 60% ee). 1H NMR (300 MHz, CDCl3): δ = 1.38 (s, 9 H), 2.17 (s, 3 H), 3.86 (d, J = 9.3 Hz, 1 H), 3.97 (dd, J 1 = 4.5 Hz, J 2 = 4.4 Hz, 1 H), 6.07 (d, J = 4.5 Hz, 1 H), 6.46 (s, 1 H), 6.63 (d, J = 7.5 Hz, 1 H), 7.05 (t, J = 7.5 Hz, 2 H), 7.19-7.31 (m, 4 H), 7.38-7.48 (m, 4 H), 7.82 (d, J = 7.2 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.5, 142.6, 141.9, 138.3, 137.5, 129.0, 128.6, 128.5, 128.3, 127.9, 127.8, 127.6, 126.9, 125.4, 101.7, 82.2, 66.3, 59.1, 28.8 ppm. IR (KBr):
ν = 3346, 2954, 2926, 2868, 17019, 1544, 1447, 1380, 1158, 840, 775, 738, 704cm-1. HRMS (Bio TOF Q): m/z calcd for C28H30N2O4Na+: 481.2098; found: 481.2098. The ee is 60% determined by HPLC [Daicel Chirapak OD-H, hexane-
i-PrOH (98:2), flow rate 1.0 mL/min]: t R = 6.10 min, 7.86 min.

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3-( p -Bromophenyl)-2-( tert -butyloxycarbonyl)-4-nitro-5,5-diphenyl-pyrrolidine (3e) Yield 65%; mp 111-112 °C; [α]D 20 -9.5 (c 0.390, CH2Cl2; 49% ee). 1H NMR (300 MHz, CDCl3): δ = 1.38 (s, 9 H), 3.84 (d, J = 6.9 Hz, 1 H), 3.95 (dd, J 1 = 12.0 Hz, J 2 = 3.0 Hz, 1 H), 5.99 (d, J = 3.6 Hz, 1 H), 6.64 (d, J = 6.3 Hz, 2 H), 7.20 (d, J = 5.4 Hz, 1 H), 7.25 (t, J = 6.1 Hz, 1 H), 7.31 (dd, J 1 = 1.6, J 2 = 4.9 Hz, 2 H), 7.37-7.44 (m, 4 H), 7.78 (d, J = 8.1 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.1, 142.4, 141.6, 136.6, 131.8, 129.6, 129.2, 128.5, 127.9, 127.8, 126.8, 125.4, 121.7, 101.5, 82.5, 65.0, 58.3, 27.9 ppm. IR (KBr): ν = 3464, 3312, 2972, 2929, 1728, 1549, 1487, 1449, 1366, 1337, 838, 786, 747, 707 cm-1. HRMS (Bio TOF Q): m/z calcd for C27H27BrN2O4Na+: 545.1046; found: 547.1008. The ee is 49% determined by HPLC [Daicel Chirapak OD-H, hexane-i-PrOH (98:2), flow rate 1.0 mL/min]: t R = 7.53 min, 8.93 min.

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3-( p -Chlorophenyl)-2-( tert -butyloxycarbonyl)-4-nitro-5,5-diphenyl-pyrrolidine (3f)
Yield 63%; mp 121-122 °C; [α]D 20 -9.0 (c 0.334, CH2Cl2; 46% ee). 1H NMR (300 MHz, CDCl3): δ = 1.38 (s, 9 H), 3.83 (d, J = 9.3 Hz, 1 H), 4.00 (dd, J = 4.8 Hz, 1 H), 6.00 (d, J = 4.8 Hz, 1 H), 6.71 (d, J = 8.4 Hz, 2 H), 7.15-7.26 (m, 4 H), 7.29 (t, J = 5.4 Hz, 2 H), 7.37-7.45 (m, 4 H), 7.79 (d, J = 9.0 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.2, 142,4, 141.7, 136.1, 133.6, 129.7, 129.2, 129.1, 128.8, 128.5, 127.9, 127.7, 126.8, 125.4, 101.5, 82.5, 66.1, 58.2, 28.8 ppm. IR (KBr): ν = 3311, 2953, 2971, 2867, 1729, 1592, 1549, 1523, 1490, 1449, 1365, 1339, 837, 786, 745, 706 cm-1. HRMS (Bio TOF Q): m/z calcd for C27H27ClN2O4Na+: 501.1552; found: 501.1530. The ee is 46% determined by HPLC [Daicel Chirapak OD-H, hexane-i-PrOH (98:2), flow rate 1.0 mL/min]: t R = 7.04 min, 8.82 min.

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3-( p -Fluorophenyl)-2-( tert -butyloxycarbonyl)-4-nitro-5,5-diphenyl-pyrrolidine (3g) Yield 49%; mp 106-107 °C; [α]D 20 -42.4 (c 0.118, CH2Cl2; 40% ee). 1H NMR (300 MHz, CDCl3): δ = 1.37 (s, 9 H), 3.83 (d, J = 9.3 Hz, 1 H), 4.01 (dd, J = 5.1 Hz, 1 H), 6.01 (d, J = 5.1 Hz, 1 H), 6.75 (q, J = 5.1 Hz, 2 H), 6.85-6.88 (m, 2 H), 7.22-7.31 (m, 5 H), 7.37-7.44 (m, 4 H), 7.79 (d, J = 8.1 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.2, 163.8, 142.5, 141.6, 133.2, 129.6, 129.5, 129.1, 128.5, 127.9, 127.8, 126.9, 125.5, 115.8, 115.5, 101.6, 82.5, 66.1, 58.1, 27.9 ppm. IR (KBr): ν = 3457, 3311, 2970, 2928, 1729, 1550, 1509, 1367, 1340, 1152, 838, 758, 745, 706 cm-1. HRMS (Bio TOF Q): m/z calcd for C27H27FN2O4Na+: m/z = 485.1847; found: 485.1822. The ee is 40% determined by HPLC [Daicel Chirapak OD-H, hexane-i-PrOH (99:1), flow rate 1.0 mL/min]: t R = 8.34 min, 12.60 min.

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3-Thienyl-2-( tert -butyloxycarbonyl)-4-nitro-5,5-diphenyl-pyrrolidine (3h) Yield 50%; mp 123-124 °CC; [α]D 20 -5.3 (c 0.432, CH2Cl2; 57% ee). 1H NMR (300 MHz, CDCl3): δ = 1.44 (s, 9 H), 3.90-3.93 (d, J = 8.4 Hz, 1 H), 4.30 (dd, J 1 = 3.8 Hz, J 2 = 3.9Hz, 1 H), 6.12 (d, J = 4.2 Hz, 1 H), 6.45 (d, J = 3.6 Hz, 1 H), 6.82 (d, J = 3.6 Hz, 1 H), 7.11 (q, J = 1.2 Hz, 1 H), 7.25 (d, J = 3.3 Hz, 4 H), 7.35 (d, J = 8.1 Hz, 2 H), 7.46 (d, J = 1.5 Hz, 2 H), 7.77 (d, J = 1.5 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 170.1, 141.9, 141.6, 140.5, 132.4, 130.0, 129.0, 128.5, 128.2, 127.9, 126.9, 126.8, 125.9, 125.4, 125.0, 101.2, 82.6, 67.3, 53.4, 27.9 ppm. IR (KBr): ν = 3438, 3322, 2979, 2932, 1731, 1551, 1366, 1341, 1154, 1129, 838, 779, 747, 707, 698 cm-1. HRMS (Bio TOF Q): m/z calcd for C24H26N2O4SNa+: 473.1472; found: 473.1479. The ee is 57% determined by HPLC [Daicel Chirapak OD-H, hexane-i-PrOH (95:5), flow rate 1.0 mL/min]: t R = 5.18 min, 6.17 min.