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

The incorporation of trifluoromethyl groups into organic
molecules
such as agrochemicals and pharmaceuticals has attracted a significant
amount 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 aryl
alkenes has been reported, which typically requires precious Ru/Ir-containing
photocatalytic systems. Herein, we report a metal-free organic photocatalyst
composed of a bibenzothiazole core and two imine-bridged methoxyphenyl
substituents (dBIP–OMe), which is able to drive
trifluoromethylative bifunctionalization of alkenes photocatalytically
without the use of any sacrificial reagents. Mechanistic studies reveal
two 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 trifluoromethylative
bifunctionalization strategy using dBIP–OMe is
applicable for both aryl and aliphatic alkenes. Furthermore, a variety
of nucleophiles, such as H2O, acetate, cyanide, azide,
etc., can be readily incorporated into the carbocation intermediate
once the foremost trifluoromethylation step is accomplished, substantially
broadening 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 demonstrated
that the hydroxytrifluoromethylation of styrene could be achieved
using an inexpensive 740 nm LED as the sole light source.