IsoquinoliniumN-Arylimides and Some Cycloadditions to Heterocumulenes

The red isoquinolinium N-arylimides 19−23 are azomethine imines of which the C=N bond is part of an aromatic ring. The N-(4-nitrophenyl)imide 22 and the N-(2-pyridyl)imide 23 were obtained crystalline; in solution the latter equilibrates with the hexahydrotetrazine 24 as its dimer. The N-phenylimide 19 is not stable; an isolated solid appears to be a tetramer. Generated by deprotonation of 11−13, the N-arylimides 19−21 undergo in situ cycloadditions to carbon disulfide, phenyl isocyanate, phenyl isothiocyanate, and diphenylketene. The storable CS2 adduct 29 offers a neutral source of theN-phenylimide 19, since a cycloreversion equilibrium is established in solution.