Oxidation of alkoxyphenols. Part XIX. Base-induced coupling of halogenophenols

Abstract

6-Bromo-4-t-butyl-o-cresol reacts with alkali to give a trimeric spiro-acetal (IV), and 2-bromo-4,6-di-t-butylphenol gives a dimeric benzoxet (VIII). 2-Bromo-4-methoxy-5-t-butylphenol gives some of the corresponding spiro-acetal (XII) but is partly demethylated. These reactions can be explained by an electron transfer from the phenoxide anion to the keto-tautomer of the phenol, and loss of bromide from the resulting radical-anion. A chain reaction ensues involving debromination of an intermediate bisbromocyclohexadienone to a dipheno-2,2′-quinone [bi(cyclohexa-2,5-dien-1-ylidene)-2,2′-quinone]. Evidence is presented in support of these proposals.