Asymmetric Reduction of Aromatic Ketones with Reagents Prepared from NaBH4 and ZnCl2 in the Presence of 1,2 : 5,6-Di-O-isopropylidene-α- d -glucofuranose

Asymmetric reduction of prochiral aromatic ketones using a freshly prepared complex derived from NaBH4, 1/3 equiv of ZnCl2, and 1,2 : 5,6-di-O-isopropylidene-α-d-glucofuranose (1) gives an excess of the corresponding (S)-alcohols in substantial optical yields (28–68%). The effects of the NaBH4/ZnCl2/1 ratio, temperature, solvent, structure of various monosaccharide derivatives, and the metal cation of the reagent on the optical yields were examined.