Catalysis Based on C−I⋅⋅⋅π Halogen Bonds: Electrophilic Activation of 2‐Alkenylindoles by Cationic Halogen‐Bond Donors for [4+2] Cycloadditions

Homo‐ and cross‐[4+2] cycloadditions of 2‐alkenylindoles, catalyzed by cationic halogen‐bond donors, were developed. Under mild reaction conditions, 3‐indolyl‐substituted tetrahydrocarbazole derivatives were obtained in good to excellent yields. Experimental and quantum calculation studies revealed that the electrophilic activation of 2‐alkenylindoles was achieved by C−I⋅⋅⋅π halogen bonds. C−I meets π: Homo‐ and cross‐[4+2] cycloadditions of 2‐alkenylindoles are reported. The halogen‐bond donor catalyst interacts with the alkenylindoles through a C−I⋅⋅⋅π interaction to provide diverse 3‐indolyl‐substituted tetrahydrocarbazoles.