Diastereoselective Reduction of Hemiacetals Derived from 2,3-O- Isopropylidene Derivatives of Carbohydrate Lactones.

Reactions of organomagnesium and/or organolithium reagents with 2,3-O-isopropylidene-D-erythronolactone and 5-O-tert-butyldiphenylsily1-2,3-O-isopropylidene-D-ribonolactone gave good yields of the corresponding hemiacetals which, by choice of hydride reagents, can be reduced stereoselectively to give products with a syn-(threo-) relationship between the new chiral centre and that at C-2 of the lactone.