Thermal ring enlargement of aromatic cyclopentadienylidene iminyl radicals. Intramolecular radical addition to the N atom of nitriles results in high yields of aza-aromatics

Abstract It has been demonstrated that ketiminyl radicals, formed at high temperatures (1000 °C, 0.3 s) in oxygen-free nitrogen from phenylhydrazones of benz-anellated cyclopentadienones (fluorenone ( 9a ), methanophenanthrenone ( 9b )), yield into phenanthridine ( 8a ) and benzo[lmn]-phenanthridine ( 8b ) in yields > 60%. The results point to a predominant addition of intermediately generated phenyl type radicals 5 to the N atom of the nitrile groups followed by bimolecular H-abstraction of the cyclic imidoyl radicals to 8 (scheme 3).