Visible-light-mediated direct difluoromethylation of alkynoates: synthesis of 3-difluoromethylated coumarins

A photoredox-catalyzed direct difluoromethylation of alkynoates has been developed. A well-designed photoredox system induces a single-step, regioselective installation of CF2H onto alkynes. Difluoromethyl sulfone was used as an easy to handle CF2H radical source to afford the desired 3-difluoromethylated coumarins in moderate to good yields via a radical-triggered tandem difluoro-methylation/5-exo cyclization/ester migration process.