Synthesis of polycyclic azonia-aromatic compounds by photo-induced intramolecular quaternization: Azonia derivatives of benzo[c]phenanthrene, [5]helicene and [6]helicene

A series of new polycyclic azonia-aromatic compounds incorporating a benzo[c]quinolizinium ring have been synthesized by photo-induced intramolecular quaternization. Acetonitrile solutions of 2-[2-(2-chlorophenyl)vinyl]quinoline 8 and 2-[2-(1-chloro-2-naphthyl)vinyl]pyridine 9 have been irradiated with a high-pressure mercury lamp through a Pyrex filter to afford the azonia derivatives of benzo[c]phenanthrene, viz dibenzo[cf]quinolizinium salt 15 and naphtho[2,1-c]quinolizinium salt 18, respectively. On photoreaction of 2-[2-(1-chloro-2-naphthyl)vinyl]quinoline 10 and 2-[2-(2-chlorophenyl)vinyl]benzo[h]quinoline 11 two successive cyclizations occur: the first converting substrates 10 and 11 into 10b-azonia[5]helicene salt 19 by photo-induced intramolecular quaternization and the second converting the salt 19 into 4c-azoniabenzo[ghi]perylene salt 20 by oxidative photocyclodehydrogenation. The photo-induced intramolecular quaternization of 2-[2-(2-chlorophenyl)vinyl]-1,10-phenanthroline 12 gives 10-aza-10c-azonia[5]helicene salt 21. The 12c-azonia[6]helicene salts 30 and 31, in which a carbon atom of the inner helix skeleton of [6]helicene is replaced by a quaternary nitrogen atom, have been synthesized by photo-induced quaternization of the corresponding olefins 13 and 14, respectively.