The mechanism of, and the solvent effects in, the glycosidation of D-glucosyl chlorides having a non-participating group at C-2, using silver perchlorate as catalyst

Abstract

The mechanism of, and the solvent effects in, the Koenigs—Knorr reaction of D-glucosyl chlorides having a non-participating group at C-2, using silver perchlorate as principal catalyst, were investigated. When a large excess of methanol was used, methyl D-glucopyranosides with inversion of the configuration at C-1 were predominantly obtained, except in one case. When 1 molar equivalent of nucleophile, such as methanol, methyl trityl ether, or 2-propanol, was used, the ratio of α- and β- D-glucopyranosides obtained varied with the solvent used. It is proposed that the reactions proceed via a common intermediate such as a D-glucosyl-perchlorate. The following conclusions are made for the preparation of α- D-glucopyranosides: anhydrous ether is a preferable solvent, silver perchlorate and sym-collidine are superior to a mixture of silver perchlorate and silver carbonate in the presence of Drierite, β- D-glucosyl chloride is preferred to the α- D anomer, and the solvent and reagents should be as dry as possible.