Rearrangements of aromatic carbonyl arylhydrazones of benzene, naphthalene, and azulene

Abstract

Aromatic carbonyl arylhydrazones have been shown to undergo two kinds of rearrangement in polyphosphoric acid both involving nitrogen–nitrogen bond cleavage. The first proceeds via insertion of the imine portion in the position ortho to the second nitrogen atom to give o-phenylenediamine intermediates: their evolution depends on the nature of the starting substrate. This reaction has been employed for synthesizing the quinoxalines (5) and the phenanthridines (11), and was demonstrated to be intramolecular. The second reaction path is a [5,5]sigmatropic rearrangement exclusive to electron-rich aromatic carbonyl hydrazones.