Synthesis of Pyrroles and Pyridines by Cyclization of N-Propargylic β-Enaminones

Significance

Reported is a synthesis of pyrroles and pyridines by intramolecular cyclization of N-propargylic β-enaminones. A minimal change of conditions - replacement of base catalysis by copper - causes regioselective cyclization preference to pyrroles or pyridines, respectively, in fair to excellent preparative yields. The ring-closure pathways are proposed to involve base-catalyzed 5-exo-dig cyclization for pyrrole formation and transition-metal-catalyzed 6-endo-dig cyclization for pyridine formation.