Synthesis of O-Heterocycle Spiro-Fused Cyclopentaquinolinones and Cyclopentaindenes through Visible Light-Induced Radical Cyclization Reactions

Presented herein is an effective and sustainable synthesisof O-heterocycle spiro-fused cyclopentaquinolinoneand cyclopentaindenederivatives through light-driven cascade reactions of N-(o-ethynylaryl)acrylamides or 2-(2-(phenylethynyl)benzyl)acrylatewith various O-heterocycles. Experimental mechanisticstudies revealed that these reactions are initiated by visible light-inducedradical formation from O-heterocycle and its regioselectiveaddition onto the acrylamide or acrylate moiety followed by 6-exo-dig and 5-endo-trig cascade radical annulation, which is terminated bysingle electron oxidation and proton elimination. Compared with previouslyreported synthetic methods for similar purposes, this newly developedprotocol has advantages such as a broad substrate scope, extremelymild reaction conditions, excellent atom-economy, high efficiency,and good compatibility with diverse functional groups. With all ofthese merits, this method is expected to find wide applications inthe related research arena.