1,3-dipolar cycloadditions, part 110 - 1,3-cycloadditions of pyridinium N-arylimides

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/cycloreversio n equilibria, in contrast to the cycloadditions of isoquinolinium N-arylimi des; enamines do not react with 5. The cycloadducts of 5a to dimethyl malea te, fumaronitrile, and acrylonitrile are N-beta-dienyl-phenylhydrazines, wh ich undergo a hydrazo rearrangement affording animals derived from a tetrac yclic system. Like enamines, the dienehydrazine system of the cycloadducts reacts with dimethyl acetylenedicarboxylate by [2 + 2] cycloaddition and el ectrocyclic ring opening furnishing tetrahydropyrrolo[3,2-a]azocine derivat ives. (C) 1999 John Wiley & Sons, Inc.