Visible Light Catalyzed Radical Cascade Cyclization Of Unsaturated Carbon-carbon Bonds To Construct Cyanomethylated/fluoroalkylated Nitrogen-containing Polycyclic Compounds

As a class of important compounds with heterocyclic skeletons,nitrogen-containing polycyclic compounds are widely present in organic drugs,natural products and organic functional materials.Therefore,the construction of this skeleton has attracted great attention from many chemists.Because visible light has the obvious advantages of environmental friendliness,easy availability,and sustainable development,visible light catalysis has been extensively studied in organic synthesis.Compared with traditional organic synthesis methods,the synthesis catalyzed by visible light have indeed shown superiorities of greenness and environment friendly.It will be a green and environmentally friendly strategy for the construction of nitrogen-containing polycyclic compounds catalyzed by visible light.In this thesis,not only the two new bonds were successfully constructed through the free radical cascade cyclization of olefinic amides catalyzed by visible light,but also benzoxazines and benzimidazoles were obtained.In the second chapter of this thesis,we studied the reaction of fac-Ir（ppy）₃ catalyzed radical cascade cyclization of olefinic amides with bromoacetonitrile under visible light irradiation to form cyanomethylated benzoxazines.Based on the template reaction,we optimized the solvents,photocatalysts,additives,lamp sources,and feed ratios,and obtained the optimal reaction condition.Under the optimal reaction condition,26cyanomethylated benzoxazines were prepared,indicating that the method has a good scope of substrates.Control experiments such as free radical capture experiments,fluorescence quenching experiments,and previous work show that bromoacetonitrile is reduced to the cyanomethylated radical by excited fac-Ir（ppy）₃ under visible light irradiation.Then,the cyanomethylated radical attacks the carbon-carbon double bond of the olefinic amide and generates new carbon radicals.The new carbon radicals are oxidized by the oxidized fac-Ir（ppy）₃ to carbocation,and finally cyclized and deprotonated to obtain cyanomethylated benzoxazines.This method first reported the synthesis of cyanomethylated benzoxazines under visible light irradiation,and provided a green,clean and environmentally friendly new method for the synthesis of cyanomethylated benzoxazines.In the third chapter of this thesis,we studied the reactions of fac-Ir（ppy）₃ catalyzed radical cascade cyclization of olefinic amides with bromoacetonitrile,ethyl bromodifluoroacetate or trifluoromethanesulfonyl chloride under visible light irradiation,and successfully synthesized cyanomethylated,difluoromethylated,trifluoromethylated benzimidazoles.The optimal reaction condition was obtained by screening the reaction solvents,photocatalysts,additives,etc.,and 27 new functionalized benzimidazole compounds were prepared under the optimal reaction condition,which indicates that the reaction has a wide range of substrates.Based on a series of control experiments,we proposed the following reaction mechanism:bromoacetonitrile,ethyl bromodifluoroacetate,or trifluoromethanesulfonyl chloride are reduced to corresponding radicals by excited fac-Ir（ppy）₃ under visible light irradiation,and finally functionalized benzimidazoles are obtained via radical cascade cyclization and aromatization.This is the first report on the construction of cyanomethylated,difluoromethylated,trifluoromethylated benzimidazole skeletons catalyzed by visible light.This method provides a novel,green,mild and effective strategy for the construction of cyanomethylated,difluoromethylated,trifluoromethylated benzimidazoles.