Synthesis and glycosylation of pyrimidin-2-yl 1-thio-α-d-manno- and -α-l-rhamnopyranoside

Pyrimidin-2-yl 2,3,4,6-tetra-O-benzyl-1-thio-α-d-mannopyrano side (9), pyrimidin-2-yl 2,3,4-tri-O-benzyl-α-l-rhamnopyranoside (10), pyrimidin-2-yl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-α-d-mannopyranoside (7), and pyrimidin-2-yl 2-O-acetyl-3,4-di-O-benzyl-1-thio-α-l-rhamnopyranoside (8) were prepared almost quantitatively from the corresponding protected 1,2-O-methoxyethylidene-β-d-manno-or-β-l-rhamnopyranose with 2-mercaptopyrimidine in the presence of mercuric bromide. Coupling reactions of the thioglycosides promoted by silver triflate with suitable glycosyl acceptors afforded 1,2-trans linked disaccharides.