Solvent-controlled 4CzBnBN-catalyzed intramolecular photocyclization and dehydrogenative photocyclization of indole carboxamides for the switchable synthesis of indoloquinolones and dihydroindoloquinolones

Abstract

Indoloquinolones and dihydroindoloquinolones are in-demand motifs in medicinal chemistry, yet methods for the controlled synthesis of both molecules are scarce. We detail the solvent-controlled switchable photocyclization and dehydrogenative photocyclization of heterocyclic anilides for the rapid and divergent synthesis of indoloquinolinones and dihydroindoloquinolinones. By using 4CzBnBN and DCM/MeOH as the catalytic system, a photocyclization reaction is achieved with excellent diastereoselectivity and good yields, resulting in the cis-selective synthesis of dihydroindoloquinolinones exclusively. Upon changing the solvent to DCE/DMSO, the reaction pathways switch to dehydrogenative photocyclization that provided indoloquinolinones. The success of this reaction hinges on the photophysical properties of the photocatalyst and its combination with specific solvents. Mechanistic studies including Stern–Volmer quenching studies, isotope labeling experiments, Volhard titration methods and DFT calculations have revealed that an energy transfer process is involved in the photocyclization reaction, while both energy transfer and electron transfer processes occur during the dehydrogenative photocyclization reaction. Our research not only provides a novel strategy for the synthesis of medicinally intriguing molecules of indoloquinolinones and dihydroindoloquinolinones but also offers insights into the modulation of catalytic performance of cyanocarbazole-based catalysts.