Ethanol's Dual Role as a Mediator and Green Solvent in Photocatalytic Hydrogen Atom Transfer-Enabled Formal Ring-Closing Metathesis toward 2-Quinolinones.

Ethanol, a widely available, low-cost, and environmentally friendly biomass-derived platform molecule, holds untapped potential beyond its conventional use as a solvent. Herein, we report a visible-light-induced hydrogen atom transfer approach that harnesses ethanol's dual function as a mediator and green solvent to accomplish the formal ring-closing metathesis of o-cyano and o-alkynyl acrylamides. This transition metal- and oxidant-free protocol provides efficient access to biologically important 2-quinolinones. Mechanistic studies support a pathway in which ethanol mediates key C=C bond cleavage via an in-situ-generated α-hydroxyethyl radical, and a plausible reaction mechanism for this transformation is proposed.