Regioselective glycosylation of 3,6-unprotected mannoside derivatives: fast access to high-mannose type oligosaccharides

A regioselective glycosylation of 3,6-unprotected mannoside acceptors was investigated. With glycosyl trichloroacetimidate donors, when an excess of trimethylsilyl trifluoromethanesulfonate is used as the catalyst, 6-O-glycosylation exclusively occurred affording a silylated disaccharide that could be involved in a subsequent glycosylation reaction. As an illustration, the fast synthesis of two trisaccharides and one pentasaccharide was achieved.