A Visible-Light-Induced α-Aminoalkyl-Radical-Mediated Halogen-Atom Transfer Process: Modular Synthesis of Phenanthridinone Alkaloids

A halogen-atom transfer (XAT) strategy utilizing α-aminoalkyl radicals allows the generation of aryl radicals at room temperature, which is applied for intramolecular cyclization reactions en route to biologically relevant alkaloids. Starting from simple halogen-substituted benzamides under visible light irradiation in the presence of an organophotocatalyst (4CzIPN) and nBu₃N allows the modular construction of the phenanthridinone core, which gives facile access to drug analogs and alkaloids, e.g., from the Amaryllidaceae family. The reaction pathway most likely involves a quantum mechanical tunneling enabled transfer event to achieve aromatization-halogen-atom transfer.