The formation of relatively stable protonated anion-radicals in the cathodic hydrogenation of quinonemethides

Abstract

Examination of the cathodic hydrogenation of two examples of quinonemethides reveals an unusual pathway in which the anion radicals of the quinonemethides fuchsone and its dimethyl analogue are protonated reversibly at oxygen by substituted phenols in DMSO to give relatively stable triarylmethyl radicals which are not reduced at the first reduction potential of the quinonemethides; this behaviour contrasts with that usually found, i.e. anion-radicals are usually formed at more cathodic potentials than reduction potentials of radicals derived from them by protonation.