Transition‐Metal‐Free Synthesis of N‐Substituted Phenanthridinones and Spiro‐isoindolinones: C(sp2)−N and C(sp2)−O Coupling through Radical Pathway

Abstract Iodine‐mediated intramolecular coupling of C−H and N−H bonds through radical pathways has been achieved for the synthesis of substituted phenanthridinones from 2‐phenylbenzamides using iodine, succininmide and di‐ tert ‐butylperoxide (DTBP) oxidant in dichloroethane at 130 °C. The developed protocol provides substituted phenanthridinones, particularly N‐alkyl substituted, which are difficult to access either by base‐mediated or transition‐metal‐catalyzed methodologies due to acidic nature of the C−H bond adjacent to nitrogen atom in the amides. Serendipitously, switching the oxidant from DTBP to phenyliodine(III) diacetate (PIDA) afforded spiro‐isoindolinones, involving intramolecular C−N, intermolecular C−O coupling and dearomatization of the phenyl ring in one pot.