A catalytic and stereoselective glycosylation with glucopyranosyl fluoride by using various protic acids

A catalytic and stereoselective glycosylation with glucosyl fluoride was effectively performed by using a catalytic amount of various protic acids. When the glycosylation was carried out, for example, using perchloric acid (HClO₄) in diethyl ether (Et₂O), the major products were α-glycosides while β-stereoselectivity was observed when tetrakis(pentafluorophenyl)boric acid [HB(C₆F₅)₄] was used in a mixed solvent of trifluoromethylbenzene (BTF)-pivalonitrile (^tBuCN) = (5:1). The stereoselectivity was controlled 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-.