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 s−1 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.. Copyright © 2002 John Wiley & Sons, Ltd.