Stannylene‐Mediated Regioselective 6‐O‐Glycosylation of Unprotected Phenyl 1‐Thioglycopyranosides

Abstract

AbstractA straightforward procedure is described for the synthesis of (1→6)‐linked saccharides by regioselective glycosylation of unprotected glycosyl acceptors. Phenyl 1‐thioglycopyranosides derived from D‐glucose, D‐galactose and D‐mannose were treated with dibutyltin oxide to introduce a stannylene acetal, and then subjected to selective glycosylation at the 6‐position with the Koenigs–Knorr protocol. Peracylated glycosyl bromides of D‐glucose, D‐galactose, D‐mannose and D‐glucosamine were employed as the donors to give the corresponding (1→6)‐linked disaccharides in moderate to good yields. The best results were obtained with glycosyl donors and acceptors derived from D‐glucose and D‐galactose. Fully acylated disaccharide thioglycosides could also serve as glycosyl donors for the regioselective coupling. Brominolysis and subsequent Koenigs–Knorr coupling with the stannylene acetal of phenyl 1‐thio‐β‐D‐glucopyranoside gave rise to the corresponding (1→6)‐linked trisaccharides in moderate yields.