Anodic oxidation of phenolic compounds. Part 5. Anodic methoxylation of phenols. A simple synthesis of quinones, quinone acetals, and 4-methyl-α-methoxycyclohexa-2,5-dienones

Abstract

The products and yields obtained on anodic oxidation in methanol of a series of phenols (1a–h) have been investigated as a function of anode material, anode potential, methanol concentration, supporting electrolyte, temperature, and substituents. ortho- and para-Methoxylated and dimeric products were observed. However, experimental conditions were found which, in favourable cases, allow selective formation of para-methoxylated products (isolated as a para-dienone or para-benzoquinone), ortho-methoxylated products (isolated as an ortho-dienone or the Diels–Alder adduct of this dienone), or dimeric products. The methoxylated products are formed via nucleophilic attack of methanol on an anodically generated phenoxylium ion; the dimeric products are probably formed by dimerisation of anodically generated phenoxyl radicals.