Synthesis of 3-O Substituted D-Mannoses

1,2,4,6-Tetra-O-acetyl-3-O-benzyl-α-D-mannopyranose (7) was obtained in good yield from 3,4,6-tri-O-benzyl-1,2-O-(1-methoxyethylidene)-β-D-mannopyranose (1) by acetolysis. Hydrogenolysis of 7 afforded 1,2,4,6-tetra-O-acetyl-α-D-mannopyranose which is a versatile intermediate for the preparation of other 3-O-substituted D-mannoses, such as 3-O-methyl-D-mannose and 3-O-α-D-mannopyranosyl-D-mannose. 3,4-Di-O-methyl-D-mannose was readily prepared from 1,2,6-tri-O-acetyl-3,4-di-O-benzyl-α-D-mannopyranose, which was also obtained from 1 by controlled acetolysis.