Chemical and electrochemical synthesis of quinoneimine n-oxides from indolinone-3-arylimino nitroxide radicals

2,2-Diphenyl-3-arylimino-indoline-1-oxyls are efficiently converted to the corresponding isomeric 5- and 7-quinoneimine N-oxides either by chemical (cerium ammonium nitrate) or electrochemical oxidation in aqueous acetonitrile. The electrochemical studies indicate that mono-electronic oxidation of the starting compounds leads to the corresponding oxoammonium ions. These are stable in anhydrous acetonitrile, as indicated by cyclic voltammetry, but in non-anhydrous conditions undergo rapid nucleophilic attack by water molecule followed by further oxidation to the final products. The relative economic and practical advantages of the electrochemical unvs the chemical process are discussed. The ESR parameters for the new nitroxide radicals involved in the present investigation are also reported. © 1988.