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.本研究采用密度泛函理论（DFT），对乙酸钯（Pd(OAc)₂）催化的串联氧化乙酰氧基化/邻位C–H活化/碳环化反应的机理展开了系统探究。文中详细讨论了氧化乙酰氧基化与邻位C–H活化之间的潜在竞争反应路径、涉及外球与内球乙酸根配体的C–H活化过程，以及二甲基亚砜（DMSO）在反应中的作用。计算结果表明，在无DMSO作为钯配位配体的中性反应体系中，该串联反应的氧化乙酰氧基化步骤优先于邻位C–H活化发生。氧化乙酰氧基化步骤与钯羧酸酯催化的sp²杂化C–H活化步骤均涉及六元环过渡态。外球乙酸根离子与钯的配位可降低邻位sp² C–H活化步骤的反应能垒。此外，本理论研究证实，作为共溶剂且与钯配位的二甲基亚砜（DMSO）可降低C–H活化步骤的能垒，同时使反应串联序列转变为邻位C–H活化/氧化乙酰氧基化/碳环化反应。