Copper‐Catalyzed Domino Homologation and Cycloisomerization Reactions for 3‐Pyrroline Synthesis

Abstract Copper bromide was found to be an efficient catalyst for a domino reaction sequence leading to 3‐pyrrolines. The Cu(I)‐catalyzed Crabbé reaction of propargyl sulfonamide and selective cycloisomerization of the allene intermediate were carried out using microwave irradiation conditions affording a wide range of 2‐substituted‐ and 2,5‐disubstituted‐3‐pyrrolines. Mechanistic studies of the reaction intermediates revealed two possible reaction pathways; both invoke the importance of vinyl copper intermediates.