Copper(II)-Catalyzed Domino Synthesis of Indolo[3,2- c]quinolinones via Selective Carbonyl Migration

A Cu(II)-catalyzed domino process involving the carbene N-H insertion, intramolecular aldol-type trapping and unprecedented ring-expansion of oxindole core through C3-selective 1,2-carbonyl migration is described for the synthesis of indolo[3,2-c]quinolinones. This tetracyclic core, having an all-carbon quaternary center, was efficiently synthesized in high yields from amines and 3-diazo-oxindoles. Mechanistic studies revealed that this reaction proceeds via a stepwise pathway and the involvement of the synergistic catalysis between Lewis acidic copper and hidden Brønsted acidity of in-situ-formed TfOH traces.