The steric effect and enantioselectivity of chiral 2,2-disubstituted thiaprolinol derivatives as ligands for borane reduction of aromatic ketones and for diethylzinc addition to aromatic aldehydes

Abstract

A new series of chiral amino alcohols 3a-e has been prepared from natural amino acid L-cysteine. These compounds have been used as chiral ligands for borane reduction of ketones and for diethylzinc addition to aldehydes. In the reduction of ketones, 3b-e have been used as the substitute of ( R)-prolinol to provide ( S)-alcohols in good yields and modest enantioselectivity (30–50% ee). In the diethylzinc addition to aldehydes, 3b-e promoted the formation of ( S)-alcohols in excellent yields and medium to good enantioselectivities (60–80% ee).