Carbohydrate orthoesters. Part II. Acid-catalysed ethanolysis of 1-O-(1,1-diethoxyethyl)-2,3,4,6-tetra-O-methyl-α-D-glucopyranose

Abstract

Ethanolysis of 1-O-(1,1-diethoxyethyl)-2,3,4,6-tetra-O-methyl-α-D-glucopyranose catalysed by 2,6-dichlorobenzoic acid yielded ethyl 2,3,4,6-tetra-O-methyl-D-glucopyranosides (36·6%; β:α ratio 29·5 : 1) and 2,3,4,6-tetra-O-methyl-α-D-glucopyranose (63·3%) by parallel first-order reactions. With added salt (0·06N-lithium toluene-p-sulphonate) the glucosidic products predominated (65·2%), but the selectivity for β-glucoside formation was much less (β:α ratio 2·1 : 1). Mechanism for the reaction are discussed.