Trifluoromethylative Bifunctionalization of Alkenes via a Bibenzothiazole-Derived Photocatalyst under Both Visible- and Near-Infrared-Light Irradiation

The incorporation of trifluoromethyl groups into organicmoleculessuch as agrochemicals and pharmaceuticals has attracted a significantamount of interest because they will impact the binding ability, lipophilicity,metabolic stability, and chemical stability of the resulting molecules.Over the past few years, photocatalytic trifluoromethylation of arylalkenes has been reported, which typically requires precious Ru/Ir-containingphotocatalytic systems. Herein, we report a metal-free organic photocatalystcomposed of a bibenzothiazole core and two imine-bridged methoxyphenylsubstituents (dBIP-OMe), which is able to drivetrifluoromethylative bifunctionalization of alkenes photocatalyticallywithout the use of any sacrificial reagents. Mechanistic studies revealtwo consecutive single-electron-transfer steps between the excited dBIP-OMe ( * ), the CF3 precursor (Umemoto's reagent), and the alkene substrate.Substrate scope studies demonstrated that our trifluoromethylativebifunctionalization strategy using dBIP-OMe isapplicable for both aryl and aliphatic alkenes. Furthermore, a varietyof nucleophiles, such as H2O, acetate, cyanide, azide,etc., can be readily incorporated into the carbocation intermediateonce the foremost trifluoromethylation step is accomplished, substantiallybroadening the application scope of this photocatalytic method. Finally,taking advantage of the two-photon absorption capability of dBIP-OMe in the near-infrared region, we demonstratedthat the hydroxytrifluoromethylation of styrene could be achievedusing an inexpensive 740 nm LED as the sole light source.

Automated summary

A metal-free organic photocatalyst, dBIP-OMe, was reported for the photocatalytic trifluoromethylation of alkenes without the use of sacrificial reagents. Mechanistic studies revealed two consecutive single-electron-transfer reactions between dBIP-OMe, CF3 precursor, and the alkene substrate. The trifluoromethylative bifunctionalization strategy using dBIP-OMe was applicable for both aryl and aliphatic alkenes, and various nucleophiles could be easily incorporated into the carbocation intermediate, broadening the application scope of this photocatalytic method.