Synthesis of Enantiomerically Pure Oxiranylboronic Esters

Abstract

Enantiomerically pure oxiranylboronic esters were synthesized for the first time starting from readily available alkenyl­boronic esters. Their absolute configurations were assigned by means of spectroscopic correlations and confirmed by means of X-ray structure analysis.

Key words

boron - chiral auxiliaries - epoxidation - asymmetric ­synthesis

References and Notes

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12

Selected Data for Epoxide 3c
[α]_D ^²0 -113.5 (c 1.00, CHCl₃); mp 178 ˚C.^¹³ IR (film):
ν_max = 3437, 2939, 1446, 1383, 1198, 1074, 757, 650 cm^-¹. ^¹H NMR (600 MHz, CDCl₃): δ = 1.42 (dd, ^³ J _OH,1b = 7.2 Hz, ^³ J _OH,1a = 6.0 Hz, 1 H, OH), 1.93 (d, ^³ J _3,2 = 3.2 Hz, 1 H, 3-H), 2.93 (ddd, ^³ J _2,1b = 4.7 Hz, ^³ J _2,3 = 3.2 Hz, ^³ J _2,1a = 2.6 Hz, 1 H, 2-H), 3.02 (s, 6 H, OCH₃), 3.39 (ddd, ^² J _1b,1a = 12.1 Hz, ^³ J _1b,OH = 7.1 Hz, ^³ J _1b,2 = 4.8 Hz, 1 H, 1-H_b), 3.77 (ddd, ^² J _1a,1b = 12.5 Hz, ^³ J _1a,OH = 5.8 Hz, ^³ J _1a,2 = 2.5 Hz, 1 H, 1-H_a), 5.41 (s, 2 H, 4′-H, 5′-H), 7.26-7.35 (m, 20 H, arom. CH). ^¹³C NMR (151 MHz, CDCl₃): δ = 40.6 (C-3), 52.0 (OCH₃), 56.3 (C-2), 62.8 (C-1), 78.5 (C-4′, C-5′), 83.4 (CPh₂OMe), 127.6, 127.8, 127.9, 128.1, 128.6, 129.8 (arom. CH), 140.9, 141.0 (arom. C_ipso). ESI-MS (+): m/z (%) = 559.1 (17) [M + Na]⁺, 453.4 (95), 333.0(100). Anal. Calcd (%) for C₃₃H₃₃BO₆ (536.4): C, 73.89; H, 6.20. Found: C, 73.69; H, 6.28.
Selected Data for Epoxide 4a
[α]_D ^²0 -108.9 (c 1.02, CHCl₃). IR (film): ν_max = 2932, 1494, 1446, 1383, 1197, 1077, 758, 700 cm^-¹. ^¹H NMR (600 MHz, CDCl₃): δ = 0.85 (t, ^³ J _7,6 = 7.0 Hz, 3 H, 7-H), 1.20-1.41 (m, 8 H, 3-H, 4-H, 5-H, 6-H), 1.59 (d, ^³ J _1,2 = 3.0 Hz, 1 H, 1-H), 2.29 (m_c, 1 H, 2-H), 3.01 (s, 6 H, OCH₃), 5.37 (s, 2 H, 4′-H, 5′-H), 7.24-7.39 (m, 20 H, arom. CH). ^¹³C NMR (151 MHz, CDCl₃): δ = 14.1 (C-7), 22.7 (C-6), 26.1 (C-5), 31.8 (C-4), 33.7 (C-3), 43.8 (C-1), 51.9 (OCH₃), 56.5 (C-2), 78.1 (C-4′, C-5′), 83.3 (CPh₂OMe), 127.5, 127.6, 127.8, 128.1, 128.7, 129.8 (arom. CH), 141.0, 141.0 (arom. C_ipso). ESI-MS (+): m/z (%) = 593.7 (63) [M + H₂O]⁺, 575.4 (90), 522.8 (35), 397.6 (33), 379.2 (49), 355.4 (100). Anal. Calcd (%) for C₃₇H₄₁BO₅ (576.5): C, 77.08; H, 7.17. Found: C, 76.90; H, 7.28.
Selected Data for Epoxide 4b
[α]_D ^²0 -40.2 (c 1.42, CHCl₃). IR (film): ν_max = 2938, 1494, 1446, 1380, 1198, 1075, 755, 700 cm^-¹. ^¹H NMR (600 MHz, CDCl₃): δ = 1.95 (d, ^³ J _1,2 = 2.8 Hz, 1 H, 1-H), 3.04 (s, 6 H, OCH₃), 3.18 (d, ^³ J _2,1 = 2.8 Hz, 1 H, 2-H), 5.42 (s, 2 H, 4′-H, 5′-H), 7.10-7.42 (m, 25 H, arom. CH). ^¹³C NMR (151 MHz, CDCl₃): d = 49.2 (C-1), 51.9 (OCH₃), 56.2 (C-2), 78.2 (C-4′, C-5′), 83.3 (CPh₂OMe), 125.6, 127.6, 127.7, 127.9, 128.1, 128.5, 128.7, 129.8 (arom. CH), 138.4, 140.9, 141.1 (arom. C_ipso). ^¹¹B NMR (192 MHz, CDCl₃): δ = 31.24. ESI-MS (+): m/z (%) = 599.3 (37) [M + H₂O]⁺, 582.2 (80), 539.2 (82), 453.2 (100), 426.5 (99), 317.2 (75), 197.3 (76). Anal. Calcd (%) for C₃₈H₃₅BO₅ (582.5): C, 78.35; H, 6.06. Found: C, 78.11; H, 6.16.
Selected Data for Epoxide 4c
[α]_D ^²0 -136.7 (c 1.05, CHCl₃). IR (film): ν_max = 3448, 2938, 1446, 1381, 1198, 1075, 758, 650 cm^-¹. ^¹H NMR (600 MHz, CDCl₃): δ = 1.42 (dd, ^³ J _OH,1b = 7.0 Hz, ^³ J _OH,1a = 5.9 Hz, 1 H, OH), 1.88 (d, ^³ J _3,2 = 3.0 Hz, 1 H, 3-H), 2.50 (ddd, ^³ J _2,1b = 4.5 Hz, ^³ J _2,3 = 3.0 Hz, ^³ J _2,1a = 2.5 Hz, 1 H, 2-H), 3.02 (s, 6 H, OCH₃), 3.38 (ddd, ^² J _1b,1a = 12.1 Hz, ^³ J _1b,OH = 7.2 Hz, ^³ J _1b,2 = 4.8 Hz, 1 H, 1-H_b), 3.77 (ddd, ^² J _1a,1b = 12.4 Hz, ^³ J _1a,OH = 5.7 Hz, ^³ J _1a,2 = 2.4 Hz, 1 H, 1-H_a), 5.40 (s, 2 H, 4′-H, 5′-H), 7.24-7.39 (m, 20 H, arom. CH). ^¹³C NMR (151 MHz, CDCl₃): δ = 40.6 (C-3), 51.9 (OCH₃), 56.0 (C-2), 62.6 (C-1), 78.2 (C-4′, C-5′), 83.3 (CPh₂OMe), 127.5, 127.6, 127.9, 128.1, 128.7, 129.8 (arom. CH), 140.9, 141.0 (arom. C_ipso). ESI-MS (+): m/z (%) = 559.1 (17) [M + Na]⁺, 453.4 (95), 333.0(100). Anal. Calcd (%) for C₃₃H₃₃BO₆ (536.4): C, 73.89; H, 6.20. Found: C, 73.67; H, 6.31.

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CCDC-766999 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/deposit [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax [phone]; email: [e-mail]].