N-Aryl-O-glycosyl Haloacetimidates as Glycosyl Donors

Reaction of 1-O-unprotected tetra-O-acetyl- and tetra-O-benzyl-glucopyranose with N-aryl haloacetimidoyl chlorides in the presence of sodium hydride and 15-crown-5 afforded N-aryl-O-glucopyranosyl haloacetimidates. Mainly the -anomers were obtained in this anomeric O-acylation-type reaction. The glycosyl donor properties of these haloacetimidates were investigated with 6-O- and 4-O-unprotected glucopyranosides as acceptors. The results were compared with those obtained with the corresponding O-glucopyranosyl trichloroacetimidates as glycosyl donors and the same acceptors. It was found that N-(2-chloro-6-methylphenyl)-O-glucopyranosyl trifluoroacetimidates (16Ad, 16Bd) exhibit glycosyl donor properties closely related to those of the corresponding N-unsubstituted O-glucopyranosyl trichloroacetimidates (12A, 12B).