A catalytic and stereoselective glycosylation with glucopyranosyl fluorideby using various protic acids

A catalytic and stereoselective glycosylation with glucosyl fluoride was ef fectively performed by using a catalytic amount of various protic acids. Wh en the glycosylation was carried out, for example, using perchloric acid (H ClO4) in diethyl ether (Et2O), the major products were alpha -glycosides wh ile beta -stereoselectivity was observed when tetrakis(pentafluorophenyl)bo ric acid [HB(C6F5)(4)] was used in a mixed solvent of trifluoromethylbenzen e (BTF)-pivalonitrile ((BuCN)-Bu-t) = (5:1). The stereoselectivity was cont rolled by not only the effect of solvent but also by the nature of counter anion of the catalyst such as B(C6F5)(4)(-) or ClO4-.