Duality of the permanganate ion in the oxidation of imines. Oxidation of imines to amides

Abstract

The oxidation of imines with potassium permanganate in acetonitrile–water has been studied. The reaction gives the corresponding amide as the major product, in contrast to the oxidation of imines with potassium permanganate in methylene dichloride–water under phase-transfer conditions. A series of imines has been oxidized to the corresponding amides in reasonable yields. Several investigations have been performed in an attempt to obtain insight into the mechanism for the imine to amide oxidation. Electron spin resonance studies indicate that radicals are formed in the reaction mixture. PhCHNBu^t shows a first-order deuterium effect relative to PhCDNBu^t in the reaction with potassium permanganate. The use of [¹⁸O]water leads to an incorporation of the labelled oxygen in the amide. The mechanism for the permanganate oxidation of imines to amides is discussed; two reaction paths are considered, one in which water adds to the imine followed by an oxidation of the amino alcohol to the amide by the permanganate ion, while the other—a minor reaction path under the present reaction conditions—is an oxidation of the imine to the nitrone.