Gas-phase cyclisation reactions of 1-(2-arylaminophenyl)alkaniminyl radicals

Abstract

Flash vacuum pyrolysis (FVP) of the oxime ethers 9–11 at 650 °C (10^–2–10^–3 Torr) gives products such as the nitrile 17, carbazoles 19 and 20 and acridines 18 and 21 derived from the corresponding iminyl radicals 13–15. The mechanism proposed for the formation of the acridines involves a key hydrogen abstraction by the iminyl of the adjacent N–H atom. When this route is blocked by an N-methyl group, as in 12, alternative cyclisations ensue, yielding the dihydroquinazoline 26 (via another hydrogen abstraction process) and the benzimidazole 25 (via an iminyl–imidoyl interconversion).