Non-conventional paths in electrophilic aromatic reactions. Part VI. Chlorination of 3,5-dichloro-2,4,6-trimethylanisole and related compounds

Abstract

The electrophilic chlorination of some hexa-substituted benzenes has been investigated. Both 3,5-dichloro-2,4,6-trimethylanisole and the parent phenol lead to cyclohexadienone formation. The isomer composition of the product depends on the solvent as well as on the substrate. In trifluoroacetic acid the anisole derivative probably undergoes primary attack of the electrophile on the 4-position. The reaction kinetics show that the methyl-group transfer to the solvent occurs in a fast step subsequent to the slow formation of the intermediate benzenium ion. 2,4,6-Trichloro-3,5-dimethyl-1-R-benzenes (R Me or OMe) were found to be highly unreactive substrates. The implications of these results in connection with the mechanisms of the electrophilic side-chain chlorination of methylbenzenes and of certain demethylation reactions of anisoles are discussed.