Quinone-mediated Trifluoromethylation Of Arenes And Heteroarenes With CF₃SO₂Na Via A Metal-free Photocatalysis Under Visible Light

Since the high electronegativity of fluorine provided stability of C-F bond,the trifluoromethyl group possesses benign thermostability and lipophilicity which increase their applications in the fields of pharmaceuticals,agrochemicals and functional materials.Photocatalytic synthesis of trifluoromethyl compounds via a sustainable and green way is one of the research hotspots in organofluorine chemistry and catalytic chemistry.Quinone with powerful oxidizability and electron accepting ability is a kind of metal-free oxidant in photochemistry.In view of the above,we have established an effective way to construct trifluoromethyl compounds using CF3SO2Na as the trifluoromethyl radical source and quinones with a fully conjugated cyclic dione structure as photocatalysts under visible light irradiation.On the basis of the experimental evidence,we can draw the following conclusions:(1)Under visible light irradiation,the trifluoromethylation of arenes and heteroarenes have successfully realized by using quinone as the photo-oxidant.The photoexcited quinone(Q*)with higher redox potential could achieve the trifluoromethylated product in a higher yield correspondingly.This strong oxidizing system had a good functional group tolerance of arenes including electron withdrawing/donating groups and N/S-containing heteroarenes.(2)The capture of trifluoromethyl radical suggests that the trifluoromethylation by quinone proceeds via a free radical process.The yields of trifluoromethyl radical and trifluoromethyl compounds are linearly proportional to the number of incident photons.The excited quinones with different oxidative potentials(>0.71 eV)promoted the CF3-derivatived anion(CF3SO2-)to generate trifluoromethyl radical and made the rest part of CF3SO2-containing S transform into final inorganic product S2O42-.The trifluoromethyl radical attacked the electron-rich position of arene or heteroarene via an electrophilic substitution process,followed by the deprotonation to give the desired trifluoromethyl arene or heteroarene.(3)We introduced MnO2 as a effective catalyst for the oxidation of hydroquinones into quinones under oxygen atmosphere.The coupling of photoredox trifluoromethylation and catalytic regeneration of quinones successfully realized the continuous quinone-catalyzed trifluoromethylation system.(4)We preliminarily realized oxygenation of arenes to phenols via a hydroxyl radical process under visible light irradiation of benzoquinone.The main characteristics and innovation of this article is:Under visible light irradiation,the photoexcited quinone with different redox potential activated CF3SO2Na and generated trifluoromethyl radical.In the presence of trifluoromethyl radical,the electrophilic substitution reaction successfully occurred with the formation of trifluoromethyl arenes and N/S-containing heteroarenes.The combination of homogeneous trifluoromethylation reaction and the heterogeneous MnO2-catalyzed oxidation reaction effectively realized a new model of the coupling of quinone-mediated trifluoromethylation and traditional oxidation catalytic reaction.