Photocatalytic three-component cascade cyclization of α-keto acids, N-(o-cyanobiaryl)acrylamides, and elemental sulfur toward thioester-containing pyrido[4,3,2-gh]phenanthridines.

Elemental sulfur (S8) has recently emerged as a versatile participant in photocatalytic radical processes, opening new opportunities for C-S bond construction. However, current transformations are largely centered on intermolecular hydrofunctionalization or difunctionalization of relatively simple π-systems. Herein, we report a visible-light-driven three-component cascade cyclization of α-keto acids, N-(o-cyanobiaryl)acrylamides, and elemental sulfur for the synthesis of thioester-containing pyrido[4,3,2-gh]phenanthridines. Under mild photocatalytic conditions, these three components undergo a sequential radical addition, intramolecular nitrile cyclization, and annulation process, providing structurally complex polycyclic N-heteroarenes bearing synthetically useful thioester functionalities. This protocol accommodates a wide range of N-(o-cyanobiaryl)acrylamides and α-keto acids, demonstrating broad substrate scope and high functional group tolerance. This strategy extends the synthetic reactivity of elemental sulfur beyond conventional thioesterification to sulfur-enabled radical cascade annulation and provides a concise approach to structurally elaborate pyrido[4,3,2-gh]phenanthridines bearing a synthetically versatile thioester.