Glycosylation of N-acetylglucosamine: imidate formation and unexpected conformation.

[structure: see text] Rhamnosylation in mild conditions of a disaccharide containing N-acetylglucosamine afforded the imidate 6 while at higher temperature and concentration of promoter trisaccharide 7 was isolated. The kinetic imidate 6 was independently rearranged in 50% yield to the thermodynamic trisaccharide 7. Comparative NMR studies of 7 in CDCl(3) and DMSO-d(6) suggest the formation of a nonchair conformation in CDCl(3). The structure of 7 was confirmed through the independent synthesis of the N-acetylacetamido trisaccharide 11.