Per-O-benzoyl-1,2-O-benzylidene derivatives of pyranoses and furanoses are versatile building blocks for oligosaccharide synthesis. This feature stems from complete orthogonality of acetal and ester functionalities. De-O-benzoylation of these derivatives under basic conditions would give the corresponding 1,2-O-benzylidene derivatives with all other hydroxy groups unprotected; the latter may be, for example, alkylated under basic conditions. Acid treatment would cleanly cleave 1,2-O-benzylidene acetal, leading to the corresponding 1,2-diols, which can be acylated to give, for example, the corresponding 1,2-di-O-acetyl-or chloroacetyl derivatives and further transformed into various glycosyl donors (glycosyl bromides, thioglycosides, glycosyl imidates, etc.) with orthogonally protected O-2 (acetate or chloroacetate, in some examples).
