GAS-PHASE CYCLIZATION REACTIONS OF 1-(2-ARYLAMINOPHENYL)ALKANIMINYL RADICALS

Flash vacuum pyrolysis (FVP) of the oxime ethers 9-11 at 650 degrees C (10(-2)-10(-3) Torr) gives products such as the nitrile 17, carbazole s 19 and 20 and acridines 18 and 21 derived from the corresponding imi nyl radicals 13-15. The mechanism proposed for the formation of the ac ridines involves a key hydrogen abstraction by the iminyl of the adjac ent N-H atom. When this route is blocked by an N-methyl group, as in 1 2, alternative cyclisations ensue, yielding the dihydroquinazoline 26 (via another hydrogen abstraction process) and the benzimidazole 25 (v ia an iminyl-imidoyl interconversion).