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 carbondisulfide, phenyl isocyanate, phenyl isothiocyanate, and diphenylketene. The storable CS2 adduct 29 offers a neutral
3-cycloadditions of isoquinolinium N-phenylimide (2a) and N-(2-pyridyl)imide (2b) to twelve α,β-unsaturated carboxylic esters and nitriles proceeded at room temp. with high yields; the reactions furnished tetrahydropyrazolo[5,1-a]isoquinoline derivatives and could be visually followed by the loss of the red color. In this class of azomethine imines, the imide nitrogen of 2 is the nucleophilic center which