Aluminium triflate catalysed O-glycosidation: temperature-switched selective Ferrier rearrangement or direct addition with alcohols

A temperature-controlled mechanism switch between the Al(OTf)(3)-catalysed direct addition of alcohols or the Ferrier rearrangement reactions in some glycals is presented. The scope and limitations are investigated as are the influence of the stereochemistry and nature of the protecting groups on the glycal substrate.