Oxidative activation in aromatic substitutions. Reactions of N,N-dimethylanilines with secondary anilines promoted by thallium triacetate

The reactions of N,N-dimethyl-p-anisidine (1a), N,N-dimethylaniline (1b), a nd N,N-dimethyl-p-fluoroaniline (1c) toward secondary anilines 2(a-d)-H in the presence of thallium triacetate sesquihydrate have been studied as repr esentative of a novel oxidatively activated aromatic substitution affording 1,4-benzenediamine derivatives 3a-d. All of the substrates considered gave substitution with diphenylamine (2d-H). However, with anilines 2b,c-H, onl y 1a underwent substitution, and substrates 1b,c were practically unreactiv e. The observed differences in reactivity are well accounted for within a m echanistic framework wherein oxidative activation of both the substrate and the secondary aniline is regarded as alternatively (or simultaneously) pos sible, depending on the redox characteristics of the reactants. For instanc e, it can be stated, beyond any reasonable doubt, that reactions of 1a with 2b,c-H proceed via nucleophilic attack of the latter on 1a(+), and that th e reaction of 1a-c with 2d-H must involve the diphenylamino radical 2d.