-Acetamido-2-deoxy-d-glycopyranosides occur as common and important structural units in oligosaccharides and glycoconjugates, such as glycolipids, glycoproteins, proteoglycans, and peptidoglycans, and are associated with a wide range of biological processes.[1] Whereas 2-acetamido-2-deoxy-a-dgalactopyranose residues are linked through a glycoside bond to the side-chain hydroxy groups of serine and threonine, the majority of 2-acetamido-2-deoxy-d-glycopyranosides are found as b-linked glycosides.The most general and extensively developed strategy for the synthesis of 1,2-trans-b-glycosides of 2-amino-2-deoxysugars utilizes donors containing a participating group as the amino-protecting functionality, which is replaced by an acetyl group after the glycosidation event.[2, 3] 2-Azido-2-deoxyglycosyl donors have also been used for this purpose. [4,5] Clearly, a direct glycosidation method by using donors with the natural N-acetyl function would constitute an ideal procedure in terms of efficiency and practicality. In practice, however, the reaction of these donors, 1, generally leads to the predominant formation of oxazoline derivatives 3 through neighboring-group participation and the subsequent abstraction of a proton from the NH group (Scheme 1). [6,7] Although oxazolines can react with acceptor alcohols in the presence of Brønsted or Lewis acids to afford 2-acetamido-2-deoxy-bglycosides 4 via oxazolinium ion intermediates 2 or 5 (that is, oxazoline method [8] ), the harsh reaction conditions required for this conversion have precluded its wide application in the synthesis of complex oligosaccharides. As part of a program to extend the recently developed glycosidation method that capitalizes on diethyl phosphite as a leaving group, [9,10] we wish to report the stereoselective synthesis of 2-acetamido-2-deoxy-b-glycosides by a direct glycosidation that does not proceed via an oxazolinium ion intermediate.At the outset of this study, we explored the trimethylsilyl trifluoromethanesulfonate (TMSOTf) promoted glycosidation of 2-acetamido-3,4,6-tri-O-benzyl-2-deoxy-a-d-glucopyr-