Stereoselective aldol condensation of boron enolates to trans a, b-epoxy aldehydes

Asymmetric reduction of three different biphenyl alkyl ketones with a (R)- oxazaborolidine as catalyst was successfully carried out and the corresponding biphenyl alcohols were obtained in high yield and ee. High diastereoselectivity was achieved with C2-conformationally stable 3,3'-bis- (2-hydroxyethyl)-2,2',6,6'-tetramethoxybiphenyl and more detailed investigations evidenced a cooperative effect between stereoaxis and stereocentre.