DFT Study on the Mechanism of Tandem Oxidative Acetoxylation/Ortho C–H Activation/Carbocyclization Catalyzed by Pd(OAc)2

A density functional theory (DFT) study has been conducted to unveil the mechanisms of tandem oxidative acetoxylation/ortho C–H activation/carbocyclization catalyzed by Pd­(OAc)2. The potential competitive reaction pathways between oxidative acetoxylation and ortho C–H activation, C–H activation with outer-sphere and inner-sphere acetate ligands, and the role of DMSO in the reaction have been discussed in detail. The calculated results indicate that the oxidative acetoxylation proceeds before ortho C–H activation in this tandem reaction in a neutral system without DMSO as a ligand coordinated to Pd. A six-membered transition state is proposed in the oxidative acetoxylation step, and a six-membered transition state is proposed in the palladium carboxylate catalyzed sp2 C–H activation step. The coordination of outer-sphere acetate ion to Pd decreases the energy barrier of the step of ortho sp2 C–H activation. In addition, this theoretical work demonstrates that the cosolvent DMSO as a ligand coordinated with Pd decreases the energy barrier of C–H activation. Also, the reaction tandem sequence changes to ortho C–H activation/oxidative acetoxylation/carbocyclization induced by DMSO as a ligand coordinated with Pd.