One-Step Synthesis of Indoloquinoline Alkaloids via the Pd-Catalyzed Larock/Ligand-Accelerated C-H Activation Cascade Reaction.

Pd-catalyzed cascade annulation of 2-iodoanilines with N,3-diphenylpropiolamides was achieved, which afforded a series of indolo[2,3-c]quinolinones with good yields and functional group compatibility. Previously, the retro-synthetic routine for the indolo[2,3-c]quinolinone skeleton has often involved intramolecular disconnection of the C(sp2)-C(sp2) bond at variable positions, which necessitates the construction of an indole or quinoline reactant with multiple pre-set functionalities. Meanwhile, using the C-H activation strategy to construct indoloquinoline is limited to cases in which the reactant must be an indole bearing a nonremovable directing group. Therefore, to circumvent these limitations, we herein report a Larock/ligand-accelerated C-H activation cascade strategy to construct indolo[2,3-c]quinolinone in a one-pot fashion. This transformation for the construction of 2-amidoindole relies on the Pd-catalyzed Larock reaction, which then forms a C-N bond to afford indoloquinoline via ligand-enabled Pd-catalyzed C-H activation.