Trifluoromethyl (CF₃) group is an important backbone of various agrochemicals, pharmaceuticals, and modern medicine due to its selective binding ability, lipophilicity, metabolic and chemical stability, thus, new synthetic strategies are under development to find efficient CF₃insertion pathways. However, for the past few years, photosensitizers (PS) composed by precious Ru/Ir have been only described for generating CF₃ radical because of their facile visible-light-induced single-electron-transfer (SET) processes. In order to overcome these limitations, we have designed and synthesized a more earth-abundant, less expensive, and non-toxic organic photoredox catalyst with sufficient excited state (ES) potential that can potentially reduce CF₃⁺ without any sacrificial redox agents. We introduced a donor−π–acceptor−π–donor-conjugated structure containing a bibenzothiazole core, methoxy donors, and imine bridges in order to achieve high quantum yield (> 0.5) as well as high ES redox potentials. Such design demonstrates an enhance scope of trifluoromethylation of aryl alkenes using a metal-free PS under visible and near infrared light irradiations (λ_irr = 456, and 740 nm). Moreover, the titled organic PS can active under different solvent conditions such as Acetone/H₂O, DMF, and DMSO, leading to the different products, providing a new synthetic strategy to construct valuable bioactive compounds. Also, we observed that numerous important functional groups can be inserted to the alkene double bond alongside CF₃ group through nucleophilic addition mechanism under dry DCM condition. Stern-Volmer plot in addition to the scavenger experiment further revealed the evidence of the SET process from the organic PS to CF₃⁺togenerate CF₃ radical. This study offers new mechanistic insights into difunctionalized trifluoromethylation reactions using an economical and easily accessible metal-free photoredox catalyst.

Yujie Sun

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