FORMATION OF 1,2-CIS-α-ARYL-GLYCOSIDIC LINKAGES DIRECTLY FROM 2-ACETAMIDO-2-DEOXY-D-GLUCOPYRANOSYL ACETATE BY THE MIXED ACTIVATING SYSTEM USING YTTERBIUM(III) TRIFLATE AND CATALYTIC BORON TRIFLUORIDE DIETHYL ETHERATE COMPLEX

We found that a mixed activating system using ytterbium(III) triflate and a catalytic boron trifluoride diethyl etherate complex efficiently promoted glycosidation of the 2-acetamido-3,4,6-tri-O-benzyl-2-deoxy-alpha-D-glucopyranosyl acetate in dichloromethane at room temperature to afford 2-acetamido-2-deoxy-D-glucopyranosides in good yields along with the formation of a considerable amount of alpha-isomers. Glycosylations of the aryl alcohols as the acceptors stereoselectively afforded aryl alpha-glycosides without producing any beta-isomers.