Investigations of Glycosylation Reactions with 2-<i>N</i>-Acetyl-2<i>N</i>,3<i>O</i>-oxazolidinone-Protected Glucosamine Donors

NIS/AgOTf-promoted glycosylations with ethyl 2,3-N,O-carbonyl-2-deoxy-1-thio-β-d-glucopyranoside donors can be performed with either α- or β-selectivity by tuning the reaction conditions. Small amounts of AgOTf (0.1 equiv) and short reaction times give β-selectivity, whereas 0.4 equiv of AgOTf and prolonged reaction times afford α-linked products. NMR-monitored glycosylation and anomerization experiments show initial formation of exclusively the β-linkage, which anomerizes, through an intramolecular mechanism involving an endocyclic C−O bond cleavage, to the α-linkage.