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), and N,N-dimethyl-p-fluoroaniline (1c) toward secondary anilines 2(a-d)-H in the presence of thallium triacetate sesquihydrate have been studied as representative 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, only 1a underwent substitution, and substrates 1b,c were practically unreactive. The observed differences in reactivity are well accounted for within a mechanistic framework wherein oxidative activation of both the substrate and the secondary aniline is regarded as alternatively (or simultaneously) possible, depending on the redox characteristics of the reactants. For instance, 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 the reaction of 1a-c with 2d-H must involve the diphenylamino radical 2d.