Photo Amidoglycosylation of an Allal Azidoformate. Synthesis of β-2-Amido Allopyranosides

Photolysis of an allal C-3 azidoformate provoked intramolecular nitrene insertion into the glycal CC unit and allowed direct incorporation of alcohol nucleophiles as β-disposed substituents at C-1. The 2-amido allopyranoside products were elaborated via N-acylation and selective oxazolidinone hydrolysis, providing N-Boc-protected 2-amino sugars and simplifying stereochemical assignments. Synthesis of the potentially labile allal azidoformate was achieved via reaction of the corresponding carbonyl imidazolide with trimethylsilyl azide, facilitated by dibutyltin oxide.