Visible-light induced trifluoromethylation/cyclization cascade to access CF₃-containing pyrazolones by EDA complex

The incorporation of trifluoromethyl groups into heterocycles often significantly enhances their bioactivity, thereby driving demand for efficient synthetic methods. Herein, a novel visible-light-driven, metal-free strategy is developed for the synthesis of trifluoromethylated pyrazolones via a radical addition/cyclization cascade. Under 390-400 nm irradiation, the reaction proceeds through an electron donor-acceptor (EDA) complex between Togni's reagent II and DABCO to generate CF₃ radicals, without the need for an external photocatalyst. A wide range of N-methacryloylhydrazones are converted into the corresponding products with good to excellent yields. This method is operationally simple and scalable, and exhibits high functional group tolerance, thus providing a sustainable route to functionalized heterocycles.