Counterion Effects in a Gold-Catalyzed Synthesis of Pyrroles from Alkynyl Aziridines

Aryl-substituted N-tosyl alkynyl aziridines undergo a gold-catalyzed ring expansion to afford 2,5-substituted pyrrole products. Under certain conditions, a ring-expansion and rearrangement leads to 2,4-substituted pyrroles. The reaction pathway is determined by the counterion to the gold catalyst.