Electrochemical oxidation of aromatic ethers. Part 5. Further studies of the coupling reactions of alkoxylated aralkyl- and aryl-amides

Abstract

An electrochemical conversion of 5,6-dimethoxy-1-(3,4-dimethoxybenzyl)indoline into 6-hydroxy-5-methoxy-1-(3,4-dimethoxybenzyl)indole is described and some examples of the electro-oxidative intra- and inter-molecular coupling reactions of indoles, oxindoles and aralkyl- and aryl-amides are examined. Mechanisms are advanced to account for the products of electrolysis and the probable cause of electrode filming. The latter phenomenon often encountered in such oxidations is discussed and the structural element responsible (a benzylic methylene group adjacent to a nitrogen or oxygen atom) is identified. For certain substrates an alternative mechanisms of aryl–aryl coupling, not involving two radical cations, is proposed.