1,3-cycloadditions of pyridinium N-arylimides

Abstract

The title compounds (5a: Ar = C6H5, 5b: Ar = 2-pyridyl) are 1,3-dipoles of the azomethine imine type; their 1,3-cycloadditions are accompanied by the loss of the pyridinium resonance energy. As a consequence, the interaction with electron-deficient ethylenes gives rise to cycloaddition/cycloreversion equilibria, in contrast to the cycloadditions of isoquinolinium N-arylimides; enamines do not react with 5. The cycloadducts of 5a to dimethyl maleate, fumaronitrile, and acrylonitrile are Nβ-dienyl-phenylhydrazines, which undergo a hydrazo rearrangement affording aminals derived from a tetracyclic system. Like enamines, the dienehydrazine system of the cycloadducts reacts with dimethyl acetylenedicarboxylate by [2 + 2] cycloaddition and electrocyclic ring opening furnishing tetrahydropyrrolo[3,2-a]azocine derivatives. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 79–88, 1999