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.