Trifluoromethylation Of Arenes And Heteroarenes By Means Of Organophotoredox Catalysis

The introduction of fluorine atoms or trifluoromethyl in organic molecules will bring about significant changes in both physical and chemical properties of organic molecules. Trifluoromethyl-substituted arenes are widely used in the synthesis of pesticides, Pharmaceuticals, functional material and dye. The CF3moiety is typically built by copper or palladium compounds catalyzed cross-coupling reactions, with specific functional groups as activating group. Although great progress has achieved in recent years, there are still limitations, for example the residue copper or palladium is adverse for drug synthesis, the use of ligand, excessly expensive trifluoromethylated reagent and pre-activation of functional groups are required. Therefore, tremendous effort has been made by organic chemist to improve the efficiency in constructing the C-CF3bond.The direct trifluoromethylation of the C-H bond is promising, as it represents a more straightforward and economic method for the synthesis of trifluoromethylated compounds. The synthetic methods of building C-CF3by C-H activation reported in literatures can be divided into the following kinds:a) oxidation of C-H activation catalyzed by Pd or Cu. b) trifluoromethylation of arenes by means of the trifluoromethyl radical. We chose triflyl chloride as the CF3source and explored the trifluoromethylation of aromatic compounds catalyzed by organic dyes under the condition of visible light.We chose the coupling reaction of p-xylene and triflyl chloride as our model reaction in the optimization of solvents, catalysts, reaction time and so on. Under the conditions of50W Xenon lampλ>435nm)irradiation, using5mol%of Eosin Y as catalyst,4equiv CF3SO2Cl,3equiv K3PO4as base, acetonitrile and water as solvent, N2protection for72h, we gained the optimal results. Then we studied the the scope of substrate application. Twenty trifluoromethylation compounds were synthesized in15%-73%19F NMR yield. This reaction system isn’t sensitive to water.In all, we have developed a mild, environment friendly and efficient method in combing organic dyes which are environmentally friendly, economic and easy handling with photocatalysis to build trifluoromethylation arenes.