Manipulation of free carbohydrates via stannylene acetals. Preparation of β-per-O-acyl derivatives of d-mannose, l-rhamnose, 6-O-trityl-d-talose, and d-lyxose

A simple and high-yielding method for the preparation of 1-O-β-acyl derivatives of carbohydrates with an axial OH group at C-2 is described. It utilizes the property of unprotected carbohydrates to preferentially form 1,2-O-cis stannylene acetals, when treated with dibutyltin oxide. These acetals can be acylated with retention of configuration at the anomeric position.