Anodic oxidation of carboxamides. Part 3. The mechanism of anodic cyclization of N-methylcarbanilides

Abstract

Anodic oxidation in methanol of N-methylcarbanilides with an alkoxy-group para to the nitrogen atom (I) gives the intramolecular cyclization products, N-methylbenzoxazolium perchlorates: no cyclization product is obtained in the electrolysis of the anilides in acetonitrile. The process of cyclization was investigated by cyclic voltammetry, controlled potential electrolysis, and open circuit relaxation experiments using an optically transparent glassy carbon electrode. In spectroelectrochemical experiments on 4′-methoxy-N-methylbenzanilides (Ib–d) in methanol, accumulation of a metastable intermediate has been demonstrated. A possible reaction sequence for the formation of the benzoxazolium salts is discussed.