Chiral Oxazaborolidine-catalyzed Asymmetric Borane Reduction of Alkyl 4-Dialkylaminophenyl Ketones

A series of alkyl 4-dialkylaminophenyl ketones were prepared and reduced asymmetrically by borane under the chiral oxazaborolidine catalysis. The results indicate that the ketones show a more obvious substituent effect on the enantioselectivity than the corresponding 4-alkyl/alkoxy/alkylthiophenyl ketones in, the asymmetric reduction because of the existence of a strong coordinate nitrogen atom with the boron atom in the catalyst and borane.