Pd/NBE Cocatalyzed Modular Synthesis of 3-Alkenyl-2,3'-bisindoles and Applications in Access to Racemosin B.

A palladium/norbornene (NBE) cooperative catalysis for the modular, one-pot synthesis of 3-alkenyl-2,3'-bisindoles from 3-iodoindoles and olefins is reported. This protocol enables the concurrent formation of the C2-C3' bisindole linkage and a C3-alkenyl group, affording the desired products in high yields with a broad substrate scope. Density functional theory (DFT) calculations reveal that the addition of p-toluenesulfonic anhydride (Ts2O) accelerates the C-H activation step via an in situ anion exchange. The method's utility is showcased by the synthesis of racemosin B and analogs, featuring two consecutive one-pot reactions.