Insights into the Oxidative Palladium‐Catalyzed Regioselective Synthesis of 3‐Arylindoles from N−Ts‐Anilines and Styrenes: A Computational Study

Abstract

AbstractPalladium (Pd)‐catalyzed intermolecular oxidative annulation represents as an attractive approach to regioselective synthesis of 2/3‐arylindoles, but the unexpected regioselectivity remains to be one of the most challenging questions in this field. Herein, we present a systematically theoretical study on the Pd‐catalyzed regioselective synthesis of 3‐arylindoles from N−Ts‐anilines and styrenes with the presence of oxidant, special ligand, and benzoquinone (BQ) additive. A refined mechanism, in which the single six‐membered ring CMD‐type transition state was involved in the C−H activation of styrenes, is obviously more energetically favorable than the proposed pathway associated with the [6‐6] palladacyclic transition state in the experimental report (Youn et al., Angew. Chem. Int. Ed. 2017, 56, 1–6). The preferred reaction pathway consists of N−H deprotonation, CMD‐type C−H bond activation of styrenes, carbopalladation, BQ‐assisted β‐C−H activation, α‐C−H bond activation, and reductive elimination. With BQ additive, the carbopalladation is the key step for controlling the regioselectivity, and the favorable Pd−O coordinating bond interaction between Pd and BQ as well as the less distortion degree of styrene in the C3‐regioselective transition state determine the observed regioselectivity. The obtained computational insights should be valuable for understanding and rational design of the transition metal‐catalyzed oxidative annulation reactions with special regioselectivity.