Synthesis of aryl, glycosyl, and azido septanosides through ring expansion of 1,2-cyclopropanated sugars.

A ring-expansion methodology for the preparation of aryl septanosides, arabinofuranosyl and glucopyranosyl septanoside disaccharides, and azido septanosides is reported. A cyclopropanated adduct of the oxyglycal upon reaction with phenols, sugars, and azide led to the formation of ring-expanded septanoside derivatives. The ring expansion was found to be stereoselective with sugars, whereas phenols and the azide afforded an anomeric mixture of the ring expanded product. It was observed further that the conversion of the intermediate diketones to the diols, using NaBH(4), occurred with high diastereoselectivities for the alpha-anomers of the septanosides. This report consolidates further the generality of the oxyglycal ring-expansion method to prepare septanosides, possessing different substituents at their reducing ends.