Long-distance control in stereoselective reduction of 3-[3-(4′-bromo[1,1′-biphenyl]-4-yl)-3-keto-1-phenylpropyl]-4-hydroxy-2H-1-benzopyran-2-one: Relative configuration of prevailing diastereomer and absolute configuration of its enantiomers

摘要: Depending on the reducing agent and reaction conditions, diastereoselective reduction of 3-[3-(4′-bromo[1,1′-biphenyl]-4-yl)-3-keto-1-phenylpropyl]-4-hydroxy-2H-1-benzopyran-2-one (2) proceeds with different stereoselectivity; a surprisingly high, approximately 90% d.e. 4A is achieved NaBH4 in MeOH at low temperature. Resulting diastereomeric racemates 4B are separated their respective syn anti configurations assigned bases mechanic considerations, supported by 1H-NMR spectra conformational analysis based MM2 calculations. The diastereomer 7A, 4-OMe derivative 4A, was partially resolved acylation C(3)-OH S-(−)-camphanic acid to camphanyl ester 12 (−)-7A, leaving (+)-enantiomer 7A. assignment absolute 1R,3S-configuration (−)-7A comparison its CD spectrum those model compounds S-14 R-15, which represent partial chromophores 4-hydroxy-2H-1-benzopyran-2-one (4-hydroxycoumarin) A, 4′-bromo-1,1′-biphenyl B; exciton coupling suggested. Chirality 9:512–522, 1997. © 1997 Wiley-Liss, Inc.