Thermolysis of polyazapentadienes. Part 8. The formation of pyrroles from 1,1-dialkyl-5-aryl-1,5-diazapentadienes
Abstract
Flash vacuum pyrolysis of the 1,5-diazapentadienes (4)–(10) gave moderate yields of pyrroles together with quinolines, formed by electrocyclic ring closure with elimination. The pyrroles were formed by hydrogen transfer from an N-alkyl group, followed by cyclisation and final aromatisation of the resulting dihydropyrrole intermediate [e.g. (19)] by free-radical cleavage. The mechanism of the hydrogen transfer and cyclisation is not known with certainty, but may involve diradicals or 1,5-Bipolar intermediates.