Electrochemical oxidation of aromatic ethers. Part 4. Intramolecular coupling of diaryl esters
A series of methoxylated aryl benzoates have been converted by controlled potential anodic oxidation into intermolecularly coupled products. In the case of 4-methoxyphenyl benzoate and 4-methoxyphenyl 3-methoxybenzoate the products are ‘ortho’-coupled biphenyls and o- and p-quinones derived from them by further oxidation. In contrast to methoxylated N-benzyl-N-methylphenylacetamides, which form the corresponding dibenz[c,e]-azocin-7-ones on anodic oxidation, the analogous benzyl phenylacetates give ‘dimeric’ and ‘trimeric’ products. The mechanisms of the reactions are discussed in terms of the stereochemistry and the substitution patterns of the starting esters.