Gold(III)-Catalyzed Intramolecular Cyclization of α-Pyrroles to Pyrrolopyridinones and Pyrroloazepinones: A DFT Study

Density functional theory calculations were carried out to study the mechanisms of gold-catalyzed intramolecular cyclization reactions of terminal alkyne and phenyl-substituted alkyne tethered pyrroles leading to pyrrolopyridinones and pyrroloazepinones, respectively. The calculation results indicate that the reaction mechanisms mainly involve metal-coordination of a substrate molecule (alkyne tethered pyrrole) through the alkyne moiety, nucleophilic attack of the pyrrole’s α-carbon on the metal-coordinated alkyne, and 1,2-migration of either the carbonyl carbon or an alkenyl carbon (derived from the alkyne moiety) from the pyrrole’s α-carbon to the β-carbon, followed by a series of protodeaurylation to finally give cyclization products. Through the detailed mechanistic study, we have explained the regioselectivity and rationalized the major/minor products observed in the gold-catalyzed intramolecular cyclization reactions of alkyne-tethered pyrroles.