Thermolysis of polyazapentadienes. Part 6. Gas-phase cyclisation of 1,5-diaryl-1,5-diazapentadienes: mechanistic aspects and some synthetic applications

Abstract

The mode of formation of quinolines by gas-phase pyrolysis of 1,5-diaryl-1,5-diazapentadienes is contrasted with the thermal behaviour of 1,2,5-triazapentadienes. The mechanism involves concerted ring closure followed by a rapid 1,5-hydrogen shift to give a 3,4-dihydroquinoline intermediate, e.g.(19) or (21). Subsequent aromatisation takes place by a stepwise, free-radical process. Methylquinolines (9), (10), (12), and (13) were obtained on a preparative scale by this method.