Cascade Synthesis of Benzimidazole-Linked Pyrroles via Copper Catalyzed Oxidative Cyclization and Ketonization

A three-component
cascade reaction of 2-aminobenzimidazole, aldehyde, and terminal alkyne
has been explored for an efficient synthesis of benzimidazole-linked
tetrasubstituted pyrroles. The reaction sequence involves the formation
of propargylamine, insertion of a terminal alkyne, and a ring opening
reaction followed by an intramolecular carbonylative cyclization under
aerobic conditions. It represents a novel strategy to the construction
of CN, CC, CO bonds and a new five-membered
2-ketopyrrole ring. In this process, the reaction conditions are crucial
and an attempt to elucidate the novel reaction pathway is well supported
by X-ray crystallography.