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.
Keywords: aerobic oxidative conditions; bisindoles; cyclizative cross-coupling; o-alkynylaniline; palladium.
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