Abstract 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.