Nucleosides. Part V. General Lewis acid catalysis of glycoside anomerisation and O→N-glycosyl rearrangement

Abstract

A reinvestigation of the glucopyranosides of 5-nitro-2-pyridone has shown that treatment of the acetylated β-O-glucoside with mercuric bromide yields not only the α-O-glucoside but also the β-N-glucoside. Anomerisation and rearrangement are also brought about by other Lewis acids (stannic chloride, zinc bromide, cadmium chloride, antimony pentachloride, and titanium tetrachloride), but the two products are formed at different rates under varying conditions. This fact, together with the failure to detect any α-N-isomer, suggests that two separate mechanisms may be involved in the reaction.