Pyrolysis of quinoline-3,4-dicarboxylic anhydrides bearing 2-phenyl, 2-benzyl and 2-o-tolyl substituents: Formation of products of carbene insertion and addition

Article abstract of DOI:10.1016/S0040-4020(01)90386-2

Flash vacuum pyrolysis of 2-phenylquinoline-3,4-dicarboxylic anhydride at 800°/0.06 mm gave indeno[1,2-b]indole (30-40%), which readily added nucleophiles Y^- at C-10 to give 5,10-dihydro derivatives (Y=H, Me, Ph, NEt₂, OMe, CH(COOMe)₂ and CMe₂NO₂). Similar pyrolysis of the 2-benzylquinoline anhydride gave a 1:2 mixture of the (expected) linear 5H-benzo[b]carbazole and the (unexpected) angular 7H-benzo[c]carbazole. The isomeric 2-o-tolylquinoline anhydride on similar pyrolysis gave mainly 11H-benzo[a]carbazole (85%), isomeric benzocarbazoles (4%) and 11H-indeno[1,2-b]quinoline (2.6%). Most of these products are probably derived from exocyclic carbenes formed by aryne-carbene equilibration, but the last compound may be formed by direct aryne-methyl interaction.