Indium trichloride promoted stereoselective synthesis of O-glycosides from trialkyl orthoformates

A novel, highly stereoselective method for O-glycosylation of glycals and glycosylbromides is developed using orthoformates as acceptors in the presence of InCl3 to afford the corresponding O-glycopyranosides in 66-94% yield. Both perbenzyl and peracetyl glycals afford the corresponding 2,3-unsaturated-O-glycosides with high alpha-selectivity. Stoichiometric amounts of orthoformates are sufficient to bring about this transformation instead of large excesses of alcohols. (C) 2008 Elsevier Ltd. All rights reserved.