Synthesis of 3,4,6-Tri-O-methyl-D-glucose, -D-galactose, and -D-mannose

Reaction of 1,3,4,6-tetra-O-acetyl- D -glucose, - D -mannose, and - D -galactose with dihydropyran and p-toluenesulfonic acid in dichloromethane gave the corresponding 2-tetrahydropyranyl ethers. Deacetylation, methylation, and hydrolysis gave 3,4,6-tri-O-methyl- D -glucose, 3,4,6-tri-O-methyl- D -mannose, and 3,4,6-tri-O-methyl- D -galactose in 60, 28, and 25% overall yields, respectively. A small amount of 3,5,6-tri-O-methyl- D -galactose was also obtained.