Influence of protecting groups on the reactivity and selectivity of glycosylation: chemistry of the 4,6-o-benzylidene protected mannopyranosyl donors and related species.

The genesis and development of the 4,6-O-benzylidene acetal method for the preparation of β-mannopyranosides are reviewed. Particular emphasis is placed on the influence of the various protecting groups on stereoselectivity and these effects are interpreted in the framework of a general mechanistic scheme invoking a series of solvent-separated and contact ion pairs in dynamic equilibrium with a covalent α-glycosyl trifluoromethanesulfonate.