Electrochemically Induced Coupling Reaction Of Aryl Diazonium Salts

Aryl diazonium salts can be directly synthesized from cheap aniline,which can be prepared in large quantities and simple operation.In recent years,with the development of organic synthetic chemistry,aryl diazonium salts have been widely used.Due to their unique properties,aryl diazonium salts have become electrophilic reagents with significant research value in coupling reactions.The research on coupling reactions based on aryl diazonium salts has become very important.In the past few centuries,a series of famous reactions based on aryl diazonium salts have been discovered and developed,such as Sandmeyer reaction,SuzukiMiyaura coupling reaction,Hiyama coupling reaction and Meerwein arylation reaction.These research work laid a solid theoretical foundation for the study of aryl diazonium salt coupling reaction.At present,most known methods cannot avoid the use of transition metal catalysts and external redox reagents.Although the efficiency is high,the use of catalysts and redox reagents still poses environmental pollution problems.Therefore,it is necessary to develop some novel synthesis strategies that are more in line with the theme of green development.Organic electrosynthesis is recognized as an environmentally friendly synthesis method,which has attracted more and more attention from researchers in recent years.Organic electrosynthesis uses the transfer of traceless electrons to drive the oxidation and reduction process in the chemical reaction process,without the need to add additional redox reagents,which is also the biggest advantage different from the traditional redox reaction.In this paper,the coupling reactions of carbon-carbon bonds and carbon-hetero bonds involved in aryl diazonium were briefly reviewed,and then the synthesis of α-aryl ketones and polycyclic aromatic hydrocarbons based on organic electrochemical strategies of aryl diazonium salts was introduced in detail.The second chapter of this thesis introduces a green and efficient organic electrochemical strategy for the synthesis of α-aryl ketones.We selected 4-ethyl formate diazobenzene tetrafluoroborate and isopropenyl acetate as model substrates to screen the solvent,electrolyte,electrode and other conditions,and determined the optimal reaction conditions.The target products can be obtained for substrates containing various functional groups.A total of 20 arylation products were prepared,and the highest yield was as high as 95 %.Subsequently,we reviewed a large number of literature and proposed the possible mechanism of the reaction,which was verified by adding free trapping agent(TEMPO).In addition,this reaction can synthesize α-aryl ketones from aniline by in-situ diazotization / ’ one-pot ’ method,and can be scaled up in grams.In the third chapter of this paper,a simple,mild and transition metal-free organic synthesis strategy was introduced.The synthesis of polycyclic aromatic hydrocarbons was achieved by[ 4 + 2 ] benzocyclization.We determined the optimal reaction conditions by screening the reaction conditions of the model substrates,and then explored the substrate range under the reaction conditions,and 23 polycyclic aromatic hydrocarbons were prepared in moderate to good separation yields,with a maximum yield of 86 %.This reaction not only has good compatibility with various functional groups,but also has a wide range of substrates for some heteroaromatics(such as pyridine heterocycles,furan heterocycles).The mechanism of this reaction was explored by free radical scavenger(BHT / TEMPO).In addition,another biggest advantage of this reaction is that poly(heterocyclic)aromatic hydrocarbons can be electrochemically synthesized from aniline by in-situ diazotization / ’ one-pot ’ method and gram-scale amplification can be easily achieved by flow electrochemistry.