Novel glycosidations of glycals using BCl₃ or BBr₃ as a promoter for catalytic and stereoselective syntheses of 2-deoxy-α-glycosides

The glycosidations of silylated glycals and alcohols using a catalytic amount of BCl₃ or BBr₃ proceeded under mild conditions in a highly stereoselective fashion to afford the corresponding 2-deoxy-α-glycosides in high yields which were often found as the glycosidic components of several bioactive natural products.