Nucleophilic displacement reactions in carbohydrates. Part VI. The solvolysis of methyl 2,3-di-O-benzyl-6-O-methylsulphonyl-β-D-galactopyranoside: participation by a benzyloxy-group

Abstract

Product analysis indicates that the 3-benzyloxy-group participates in the solvolysis of methyl 2,3-di-O-benzyl-6-O-methylsulphonyl-β-D-galactopyranoside in either buffered aqueous methanol or NN-dimethylformamide. The product of solvolysis is methyl 3,6-anhydro-2-O-benzyl-β-D-galactopyranoside. This anhydro-sugar is also formed on brief treatment of methyl 2-O-benzyl-3,4-O-isopropylidene-6-O-p-tolylsulphonyl-β-D-galactopyranoside with dilute acid, presumably with neighbouring-group participation by the 3-hydroxy-group following removal of the isopropylidene group. Methyl 4,6-O-isopropylidene-β-D-galactopyranoside is formed, together with the 3,4-acetal, on acetonation of methyl β-D-galactopyranoside in the presence of anhydrous copper sulphate.