A radical route in the biomimetic oxidation of a tertiary amine

Whereas the biomimetic oxidative N-dealkylation of tertiary amines with t-BuOOH and an iron(III) tetraphenylporphyrin typically proceeds by an electron transfer (ET) route, a radical H-atom transfer (HAT) route has been found to operate with N-benzylaziridine (1), an amine that is fairly resistant towards one-electron oxidation for steric reasons. New mechanistic information is presented in favour of this radical route, and the exclusive formation of the dimeric product N,N-dibenzylpiperazine (2) is explained in the light of the Baldwin’s rules. Flash photolysis data provide a rate constant of 1.7 105 s1 for the ring opening of the aziridine radical (1.) to the imine radical (4.) in the early stages of the process leading to 2. Semiempirical calculations indicate the ring-opened radical 4. to be more stable than 1.