The $O_sO_4$-catalyzed dihydroxylations of a monosubstituted allylic amine and $gamma-amino-alpha,;eta-unsaturated$ (E)-esters with bulky alkyl groups showed a high anti-selectivity. Since the acyclic conformation of N-acyloxy protected allylic amines was efficiently controlled by a bulky t-Bu or OBO ester group, the anti diastereoselectivity of >12.5:1 was obtained without applying a chiral reagent. The synthetic utility of the present method was demonstrated by a stereoselective and efficient synthesis of an $alpha$-glucosidase inhibitor 15 from commercially available N-Cbz-L-serine 6 in 11 steps and 31% yield.