Intermediacy of a Persistent Urazole Radical and an Electrophilic Diazenium Species in the Acid-Catalyzed Reaction of MeTAD with Anisole.

Abstract

The reaction of N-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with anisole in the presence of trifluoroacetic acid affords unexpected disubstituted urazole products instead of the expected monosubstituted urazole as typically observed in the reactions of MeTAD with other substituted benzenes. Our investigation into the mechanism of formation of these disubstituted products suggests that MeTAD is capable of further reaction with the initially formed monosubstituted urazole to afford a persistent urazole radical. The identity of this radical has been established by UV-vis spectroscopy, the nature of its self-dimerization reaction, and via independent generation. Electrochemical oxidation of this radical was carried out, and the resulting diazenium ion was demonstrated to be reactive with added substituted benzenes, including anisole. When oxidation was carried out chemically using thianthrenium perchlorate in the presence of anisole it was shown to produce the same disubstituted products (and in the same ratio) as observed in the acid-catalyzed reaction. A common diazenium species is proposed to be active in both cases. We also report the synthesis and characterization of three interesting tetrazane dimers resulting from unstable urazole radicals.