Mn(Ⅲ)-Catalyzed Oxidative Dehydrogenation And Alkylation Of Nitrogen Heterocycles

Free radical reactions realized by transition metal catalysts under mild conditions have attracted much attention and made great progress in recent two decades because of their unique activity and selectivity.Among them,the free radical reaction initiated by manganese catalysts has become one of the research hotspots in this field.The new carbon–carbon and carbon–heteroatom bonding reactions catalyzed by cheap manganese have been applied to the synthesis of functional molecules such as drug molecules,functional materials and complex natural products.Nitrogen-containing heterocycles such as indole and quinoxalone widely exist in bioactive natural products,applied drugs and functional materials.The synthesis and functionalization of these compounds have attracted the attention of many chemists.This thesis aims to design and explore new types of free radical carbon–carbon and carbon–heteroatom bonding reactions that can occur under mild conditions and promoted by cheap manganese catalysts,so as to provide a new method for the clean and efficient synthesis of indole and quinoxalone derivatives with important application prospects.The details are as follows:1.Construction of a new system for oxidative dehydrogenation of indoline and tetrahydroquinoline compounds catalyzed by manganese catalystUnder mild conditions,the oxidative dehydrogenation aromatization of indoline and tetrahydroquinoline compounds was realized with air as clean oxidant and Mn（OAc）₃·2H₂O as catalyst,and the target product was obtained in good to excellent yield.The results show that the choice of solvent is very important for the reaction.For indolines containing electron-withdrawing substituents,acetic acid solvent shows the best effect;For indolines containing electron-donating substituents and N-H indoline or tetrahydroquinolines,the mixed solvent of trifluoroethanol and methanol is needed.The reaction mechanism was studied by experiments of free radical capture,intermediate separation and isotope labeling,and a possible mechanism was put forward.2.Exploration on alkylation of quinoxalonesUsing N-methylquinoxalone as the substrate and Mn（OAc）₃·2H₂O as catalyst,the methylation of quinoxalones by peroxybutyl ether was realized;The silylation reaction of the synthesized bis（trimethylsilyl）peroxide with quinoxalone compounds was explored.Unfortunately,it was found that the manganese catalyst did not achieve the expected results,but through the preliminary screening of the catalyst,it was found that the copper-based catalyst was effective in the transformation.