Synthesis of 2- O-benzyl- and 2,3- and 2,6-di- O-benzyl- D-galactose

Abstract

The following ethers, of potential value for the synthesis of α- D-galactopyranosides, were prepared: 2- O-benzyl- D-galactose, 2,6-di- O-benzyl- D-galactose, and 2,3-di- O-benzyl- D-galactose. Isopropylidenation of methyl α- D-galactopyranoside in the presence of phosphorus pentaoxide gave its 3,4-, and 4,6- O-isopropylidene derivatives. Treatment of the 3,4-acetal with trityl chloride in pyridine produced the 6-trityl ether, which was benzylated with benzyl chloride and sodium hydride in N,N-dimethylformamide to yield the 2-benzyl ether. Acid hydrolysis of this product gave 2- O-benzyl- D-galactose. Benzylation of methyl 3,4- O-isopropylidene-α- D-galactopyranoside, followed by hydrolysis, gave 2,6-di- O-benzyl- D-galactose. Similarly, 2,3-di- O-benzyl- D-galactose was obtained by acid hydrolysis of methyl 2,3-di- O-benzyl-4,6- O-isopropylidene-α- D-galactopyranoside and of methyl 2,3-di- O-benzyl-4,6- O-benzylidene-β- D-galactopyranoside.