Synthesis of O-glycopyranosyl heterocyclic ketene aminals and their use as glycosyl donors.

The synthesis and reactions of glycopyranosyl heterocyclic ketene aminals were investigated. Under mild conditions, the benzoyl-substituted heterocyclic ketene aminals 3 or 4 underwent O-glycosylation with tetra-O-acetyl-alpha-D-glucopyranosyl bromide (1) using mercuric cyanide or silver trifluoromethanesulfonate as catalyst in acetonitrile to give O-glycopyranosyl heterocyclic ketene aminals 5-7 and 8-11, respectively. The beta-anomers were the sole products. By the O-glycosylation of heterocyclic ketene aminals with 1, the O-attack of heterocyclic ketene aminals was carried out for the first time. Some of 5-11 in the synthesis of oligosaccharides 14 and 15 can provide a valuable leaving group at the anomeric position of the glycopyranosyl ring. Compounds 6c or 10c may be potentially useful as glycosyl donors in the synthesis of oligosaccharides.