Rhizobial saccharides. 2. Selective synthesis of both diastereomers of 4,6-O-pyruvylated D-glycopyranosides

Article abstract of DOI:10.1016/0040-4039(94)85023-2

Both diastereomers of 4,6-O-pyruvylated glycosides S- and R-2 were selectively prepared from the corresponding 4,6-unprotected glycosides 1 by acetalation of the latter with methyl pyruvate and BF₃-diethylether complex. In acetonitrile as the solvent, the thermodynamically favoured diastereomers having an axial-oriented methoxycarbonyl group are formed preferentially. In methyl pyruvate as the solvent, the diastereomers having an equatorial-oriented methoxycarbonyl group are the main products and the diastereoselectivity of the acetalation is influenced by the protecting groups at positions 2-O and 3-O of the starting glycosides 1.