Azulene–naphthalene-type rearrangements in Benz[a]azulene and Cyclohepta[b]indole

Flash vacuum pyrolysis (FVP) of benz[a] azulene yields phenanthrene and 2-ethynylbiphenyl. FVP of cyclohepta[b] indole similarly yields phenanthridine and 2-cyanobiphenyl. The reversibility of the reactions is demonstrated by FVP of 2-ethynylbiphenyl and 2-isocyanobiphenyl. All the observed reactions are in accord with the norcaradiene-vinylidene mechanism of the azulene-naphthalene rearrangement, whereas other proposed mechanisms are ruled out