Theoretical Insight into the Mechanism and Origin of Divergent Reactivity in the Synthesis of Benzo-Heterocycles from -Alkynylbenzamides Catalyzed by Gold and Platinum Complexes.

This work presents a DFT study on the mechanism and origin of catalyst-controlled divergent reactivity in the synthesis of benzo-heterocycles from -alkynylbenzamides by Au(I)/Pt(IV) catalysis. The results indicate that the transformations proceed via a nucleophilic cyclization process. In the Au(I) catalysis, the preferred -attack mode mainly originates from the symmetry match in the dominant bond-forming interaction between the lone-pair orbital of carbonyl-O and the in-plane alkyne π* orbital, and the electronic property of the ligand controls the -5--/-6-- selectivity. The preference for the -attack mode in Pt(IV) catalysis is attributed to the stronger coordinate capability of carbonyl-O than amino-N in the substrate to PtCl, and the regioselective -6-- or -5-- cyclization depends on the stronger electrostatic interaction between the amino-N and alkynyl-C atoms. The theoretical results provide a fundamental understanding of why and how gold and platinum complexes catalyze the cyclization of -alkynylbenzamides with different chemo- and regioselectivities.