Use of acyclic glycosyl donors for furanoside synthesis

Treatment of the peracetylated ethyl dithioacetals of D-glucose, D-galactose, and D-mannose with acetyl chloride and boron trifluoride diethyl etherate at reflux yields the known acyclic 1-chlorol-(ethylthio) derivatives. These compounds are shown to effectively glycosylate a variety of carbohydrate accepters using silver trifluoromethanesulfonate as the promotor, affording stereospecifically the corresponding acyclic O,S-acetals in good to excellent yield. Furthermore, following deacetylation, treatment of these O,S-acetals with a mixture of mercuric salts in either methanol or dimethylformamide gives rise to disaccharides terminating in D-furanosyl residues.