Stereospecific access to α- and β-N-glycosylamine derivatives by a metal free O-to-N [3,3]-sigmatropic rearrangement

Glycosylamine derivatives are biologically relevant compounds widespread in Nature, but the synthesis of this motif has been little addressed and its access with control of configuration at the anomeric carbon is challenging. Glycals substituted at C-3 with a carbamate group undergo, upon dehydration, a prompt allyl cyanate to isocyanate rearrangement to the isomeric Nglycosyl isocyanates, which can be conveniently trapped by one-pot nucleophilic addition with alcohols or amines to afford N-glycosyl carbamates and ureas, respectively. The rearrangement follows a [3,3]-sigmatropic pericyclic mechanism as illustrated by the stereospecificity of the reaction, with nitrogen being delivered at the anomeric position to the same face from which the oxygen at C-3 has departed. Thus, glucal and galactal give β-N-glycosides exclusively while allal furnishes α-N-glycosides. cis-Dihydroxylation of the synthesized unsaturated Nglycosides afford different 1-aminosugars with good selectivity