Tetrameric Electron Donor-Acceptor Complex-Mediated Cascade Cyclization for the Synthesis of Tetrahydropyridoindole

Herein, we describe a photochemical strategy for synthesizing tetrahydropyridoindoles via a cascade decarboxylative cyclization between indolyl NHPI esters and alkenes. This protocol showcased a broad substrate scope, accommodating primary, secondary, and tertiary alkyl radicals generated from decarboxylation of NHPI esters. Diverse functional groups, such as esters, amides, alkenes, cyano, trifluoromethyl, aldehyde, and sulfonyl moieties, were well tolerated. Key to the success was the identification of a tetrameric EDA complex, formed from KI, PPh₃, the substrate, and di(pyridin-4-yl)amine.