Reaction of functionalized azomethine ylides with acetylenic dipolarophiles: the facile synthesis of functionalized 2H- and 1H-pyrroles

The reaction of functionalized azomethine ylides as C-unsubstituted nitrile ylide equivalents with acetylenic dipolarophiles is mentioned. Therein, the initially formed cycloadducts, 2,5-dihydropyrroles, by the reaction of the azomethine ylides with substituted acetylenes, undergo a fission reaction to afford 2H-pyrroles and the parent heterocyclic system. Some 2H-pyrroles isomerized to 1H-pyrroles under both thermal and acidic conditions.