A diastereoselective synthesis of cyclopentanones via photocatalytic reductive alkyltrifluoromethylation of ynones

Traditional alkyne carbotrifluoromethylation protocols lead to the production of trifluoromethylated alkenes, while new reaction modes remain to be explored. Herein, a visible light induced reductive alkyltrifluoromethylation of ynones with the Langlois reagent is developed, providing a regio- and diastereoselective access to highly functionalized trifluoromethylated cyclopentanones at room temperature. Mechanistic studies suggest a radical pathway involving the regioselective trifluoromethylation of C-C triple bonds, 1,5-HAT, 5-endo-trig closure, single electron transfer reduction, and protonation.