Radical Addition/Insertion/Cyclization Cascade Reaction To Assemble Phenanthridines from N-Arylacrylamide Using Cyano as a Bridge under Photoredox Catalysis.

A radical addition/nitrile insertion/homolytic aromatic substitution (HAS) cascade reaction to prepare 6-quaternary alkylated phenanthridines was developed. The addition of the active methylene radicals which were generated from 2-bromoacetonitrile, ethyl 2-bromoacetate, 2-bromo-N,N-dimethylacetamide, or 2-bromo-1-phenylethan-1-one to carbon-carbon double bonds of N-arylacrylamides followed by the cyano-participating sequential cyclization produced a series of phenanthridines in moderate to good yields under photoredox catalysis.