Alkyloxytris(dimethylamino)phosphonium salts. Part 21. Anomeric hydroxy-group activation of 2,3:4,6-di-O-isopropylidene-α-D-mannopyranose, thioglycosylation and glycosylation

Abstract

The action of carbon tetrachloride and tris(dimethylamino)phosphine at low temperature on 2,3:4,6-di-O-isopropylidene-α-D-mannopyranose affords the α anomeric form of the corresponding alkoxytris(dimethylamino)phosphonium chloride. The condensation of aromatic thiols with this salt leads to β-thiomannosides by an SN2 process and the condensation of alcohols, preceded by the action of silver salts in order to avoid the formation of the glycosyl chlorides, yields a mixture of α- and β-mannosides.