Photo amidoglycosylation of an allal azidoformate. Synthesis of beta-2-amido allopyranosides

[GRAPHICS] Photolysis of an allal C-3 azidoformate provoked intramolecular nitrene ins ertion into the glycal C=C unit and allowed direct incorporation of alcohol nucleophiles as a-disposed substituents at C-1, The 5-amido allopyranoside products were elaborated via N-acylation and selective oxazolidinone hydro lysis, providing N-Boc-protected 2-amino sugars and simplifying stereochemi cal assignments. Synthesis of the potentially labile allal azidoformate was achieved via reaction of the corresponding carbonyl imidazolide with trime thylsilyl azide, facilitated by dibutyltin oxide.