Photocatalytic Silylation/Germylation and Cascade Cyclization of N -( o -Cyanobiaryl)acrylamides: Access to Silylated and Germylated Phenanthridines

We report a highly efficient protocol for the synthesis of silylated/germylated phenanthridine derivatives through the photocatalytic radical cascade cyclization of N-aryl acrylamides. A simple N-aminopyridinium salt was used as a hydrogen atom transfer reagent to generate a silyl/germyl radical under photoredox catalytic conditions. This method demonstrates a broad substrate scope and is suitable for the late-stage functionalization of natural products and pharmaceuticals with a shorter reaction time. Moreover, photophysical studies of selected phenanthridine derivatives highlight the promising luminescence properties with excellent fluorescence emission efficacy (quantum yields).