Aryldiazonium-Salt-Triggered Radical Alkylation/Cyclization Reaction of N-Arylacrylamides via Hydrogen Atom Transfer

Phenanthridines are a key N-heterocyclic scaffold that is widely found in numerous important functional compounds. Herein, we disclose an aryldiazonium salt-mediated radical alkylation/cyclization reaction of N-arylacrylamides with diverse C(sp³)-H partners including acetonitrile, acetone, alcohols, chlorides, cyclic alkanes, and toluene derivatives. Numerous alkylated phenanthridines are prepared with up to 77% yield without oxidants or transition-metal catalysts, showing good group tolerance. Preliminary mechanistic studies reveal that the generation of alkyl radicals proceeds through hydrogen atom transfer (HAT) between C(sp³)-H bonds and aryl radicals, which are generated in situ from aryldiazonium salts.