Dual Role of Trifluoromethyl Thianthrenium Triflate in Self-Catalyzed Phototandem Trifluoromethyl/Cyclization of <i>N</i>-Methacryloyl Aldehyde Hydrazones in EtOH

A self-catalyzed phototandem trifluoromethylation/cyclization of <i>N</i>-methacryloyl aldehyde hydrazones with trifluoromethyl thianthrenium triflate (TT-CF₃⁺OTf^-) in ethanol has been developed. This method provides access to various trifluoromethylated pyrazolin-5-ones under mild, exogenous catalyst- and organic oxidant-free conditions. The readily prepared TT-CF₃⁺OTf^- serves a dual role as both the CF₃ radical source and an internal oxidant, greatly simplifying the reaction system. The thianthrene byproduct is efficiently recovered and reused, enhancing economic viability and reducing chemical waste, in line with green chemistry principles.