Utility of Ligand Effect in Homogenous Gold Catalysis: Enabling Regiodivergent π‑Bond-Activated Cyclization

Comprehensive utilization
of both electronic and steric properties of ligands in homogeneous
gold catalysis is achieved in the regio­divergent intra­molecular
hydroarylation of alkynes. A flexible electron-deficient phosphite
ligand, combined with the readily transformable directing group methoxyl
amide, is attached to a cationic Au­(I) center in three-coordinate
mode, affording sterically hindered ortho-position
cyclization. Meanwhile, para-position cyclization
is exclusively achieved with the assistance of a rigid electron-abundant
phosphine ligand-based Au­(I) catalyst, in which ligands manifest the
compensating effect for cyclization through steric hindrance and electronic
properties. By combining gold with silver catalysts, tetrahydro­pyrrolo­quinolinones
possessing a congested tricyclic structure are obtained via a proven
Au/Ag relay catalytic process.