Catalytic Stereoselective Synthesis of Glycosides

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In the presence of a catalytic amount of tin (II) trifluoromethanesulfonate or ytterbium (III) trifluoromethanesulfonate, various 2-amino-beta-D-glucopyranosides or galactopyranosides are stereoselectively synthesized in high yields from 1, 3, 4, 6-tetra-O-acetyl-2- (2, 2, 2-trichloroethoxy-carbonylamino) -2-deoxy-beta-D-glucopyranose and galactopyranose or 1, 3, 4, 6-tetra-O-acetyl-2-allyloxycarbonylamino-2-deoxy-beta-D-glucopyranose on treatment with alkyl trimethylsilyl ethers or free alcohols.Further, 2-amino-alpha-D-glucopyranosides or galactopyranosides are respectively prepared in high yields with almost perfect stereoselections from the same glycosyl donors using a catalyst generated from tin (IV) chloride and a silver salt via an anomerization step.In the coexistence of hexamethyldisiloxane and anhydrous calcium sulfate, a catalytic amount of an activator such as tin (II) trifluoromethanesulfonate, ytterbium trifluoromethanesulfonate, lanthanum trifluoromethanesulfonate or tin (II) chloride smoothly promotes the glycosylation reactions between 1-hydroxy sugars and free alcohols, electron-rich aromatic compounds or silylated uncleophiles to produce various O-, C- or N-beta-glycosides stereoselectively in high yields whereas alpha-ribosides are obtained predominantly by the further addition of lithium perchlorate. In the case of carbon nucleophiles such as electron-rich aromatic compounds or silyl enol ethers derived from carbonyl compounds, perfect beta-selectivity is shown either in the presence or absence of lithium perchlorate.