Pd/C-Catalyzed Cyclizative Cross-Coupling of Two ortho-Alkynylanilines under Aerobic Conditions: Synthesis of 2,3’-Bisindoles

A palladium-catalyzed cyclizative cross-coupling of two o-alkynylanilines to 2,3’-bisindoles under aerobic oxidative conditions was developed. Mechanistic studies suggested that the two catalytic cycles, namely the formation of 3-alkynylindoles 8 and their subsequent cyclization to bisindoles 5, are temporally separated. The aminopalladation of 3-alkynylindoles 8 occurred only after all the N,N-dialkyl-o-alkynylanilines were consumed. The solid support (activated charcoal) played a crucial role in the second intramolecular aminopalladation process.