The in situ activation of thioglycosides with bromine: An improved glycosylation method

A one-step conversion of thioglycosides into 1,2-trans- or 1,2-cis-O-glycosides was accomplished, in situ, by treatment with bromine in the presence of a glycosyl acceptor and a promoter such as silver triflate or mercuric cyanide. This mild "one-pot" procedure gives O-glycosides in excellent yields with high stereochemical control, even with unreactive and hindered glycosyl acceptors. The reaction conditions are compatible with various protecting groups such as acetates, benzoates, benzyl ethers, N-phthalimido groups, and benzylidene acetals.