Stereoselective Synthesis of Biology-Oriented Pentacyclic Pyrrolo[2,1-a]isoquinoline Scaffolds by Photoredox-Induced Radical Annulations

We report a visible-light photoredox-induced stereoselective radical 1,3-dipolar cycloaddition between tetrahydroisoquinolines and coumarin derivatives, providing a platform for the efficient synthesis of pseudo-natural-inspired fused pentacyclic scaffolds. Using this protocol, a diverse range of valuable fused pentacyclic pyrrolo[2,1-a]isoquinolines were efficiently obtained in moderate to good yields and excellent diastereoselectivities. Mechanistic investigations including radical control experiments and light on/off studies indicated that the reaction underwent a visible-light induced radical process. The insights gained from our studies are expected to advance general efforts toward the green synthesis of biology-oriented pseudo-natural products and heterocyclic skeletons.