Activation of Alkenes via Chalcogen Bond: Chalcogen•••π Bond Catalyzed the Diels-Alder Reaction of 2-Vinylindoles

Chalcogen bond catalysis is a promising catalytic strategy, characterized by its environmental friendliness, relatively inexpensive cost, and similar reactivity to transition metal catalysis. Experimental results suggest that the S•••π and Se•••π bonds can efficiently drive the vinyl-indole-based Diels-Alder reaction (Angew. Chem. Int. Ed. 2021, 60, 9395-9400). In this work, chalcogen bond catalysis in the Diels-Alder reaction between 2-vinylindoles has been investigated based on density functional theory. For this reaction, the Te•••π bond catalysis is as an alternative catalytic strategy. The Diels-Alder reaction catalyzed by chalcogen bond is stepwise and involves two steps: the carbon–carbon bond formation process and the cyclization process. The cyclization process is the rate-determining step. From the perspective of energy decomposition analysis, the electrostatic interaction is the main factor to cause Se•••π bond catalysis, the polarization interaction is the main factor to cause Te•••π bond catalysis. Additionally, this catalytic reaction involves the endo pathway and exo pathway. The Gibbs free energy barrier values of the endo pathway are lower than those of the exo pathway, which facilitates the formation of the endo product. This study will provide a valuable perspective on the application of chalcogen bond in the activation of alkenes.