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

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 degrees 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.