Benzamidine-catalysed mutarotation of 2,3,4,6-tetra-O-methyl-D-glucose

Abstract

A comparison of the catalytic powers of benzamidine, n-butylamine, and 1,4,5,6-tetrahydro-2-phenylpyrimidine has shown that the first base is a powerful catalyst for tetra-O-methyl-D-glucose mutarotation in benzene. However, the observed high reactivity is not due to a bifunctional action of the catalyst, as benzamidine in, the same solvent is also very effective in promoting dehydrohalogenation reactions, the anti-stereochemistry of which cannot involve a simultaneous intervention of the acidic and basic functions. Therefore, the catalytic activity is attributed to the basic group only, and the results are explained in terms of a mechanism involving a glucosyloxide–benzamidinium ion pair. The difference in behaviour between the benzamidine and other tautomeric catalysts (e.g. 2-pyridone) is discussed.