One electron oxidations of benzyl and 2-phenylethyl phenyl ethers. The fate of the intermediate radical cations

Abstract

The one electron oxidations of benzyl phenyl ether ( 1 ), 2-phenylethyl phenyl ether ( 2 ) and 2-(4-methoxyphenyl)ethyl phenyl ether ( 3 ) promoted (a) by cerium(IV) ammonium nitrate (CAN) in AcOH, (b) electrochemically in AcOH-MeCN/AcOK and (c) photochemically in MeCN, in the presence of 9,10-dicyanoanthracene (DCA), have been investigated. With 1 benzaldehyde forms, under all the reaction conditions, accompanied by products of acetoxylation at the phenoxy ring (conditions a and b) or by phenyl benzoate (condition c). The CAN-promoted and the electrochemical oxidation of 2 exclusively lead to substitution at the phenoxy ring, whereas only-side-chain attack at the benzylic carbon occurs in all of the reactions of 3 , with formation of 4-methoxybenzaldehyde and products of side-chain oxidation. Phenyl 4-methoxybenzoate is also formed (conditions b and c). However, when the electrochemical oxidation is carried out in the absence of AcOK, only a product of intramolecular ring closure forms. These results allow one to draw some interesting conclusion on the competition between the various reaction pathways available to the cation radicals which are the first formed reaction intermediates in these one electron processes.