Studies On Electrochemical Halogenation Reaction Of Coumarins And α,β-Unsaturated Esters

Organic electrochemical synthesis is a frontier subject combining organic synthesis and electrochemical technology,and is one of the most popular research fields at present.It completes the redox reaction by means of electron transfer under electrochemical conditions,thus avoiding the use of additional chemical redox reagents and reducing environmental pollution.It is an efficient and green synthesis method.In addition,the organic electrochemical synthesis is easy to operate and has mild conditions.The reaction can usually be carried out at room temperature,and the atomic utilization rate is high,which meets the development requirements of green chemistry.Based on these advantages,more and more chemical workers have devoted themselves to the research field of organic electrochemical synthesis.In terms of production and application,organic electrochemical synthesis has been widely used to synthesize various organic intermediates such as fine chemicals,dyes,drugs,organic reagents,amino acids,etc.Organic halides are one of the most widely used precursors or intermediates.They are often applied to the conversion of organic functional groups.The polarization of carbon-halogen bonds and the good leaving ability of halogen atoms enable these compounds to effectively carry out nucleophilic substitution and elimination reactions.In addition,in the presence of suitable reducing agents,organic halides could act as radical precursors or can be converted to organometallic compounds.Along with their great synthetic utility,organic halides are also widely used in many valuable commercial products,such as solvents,plasticizers,fire retardants and organic light-emitting devises.In biology,the addition of halogen atoms can significantly change the biological characteristics of molecules,so that these compounds can be used in medicine,agriculture and other fields.This thesis studied the halogenation reaction of coumarin derivatives and α,β-unsaturated esters under electrochemical conditions,which mainly consists of the following three parts:In the first part,recent research and development of halogenation reaction are reviewed.The research progress of halogenation reaction is reviewed from three aspects,including transition metal catalysis,photocatalysis and electrochemistry.In the second part,coumarin derivatives are used as raw materials.Sodium chloride and sodium bromide are used as halogen sources.The chlorination and bromination reactions are studied under electrochemical conditions.Under the optimal reaction conditions,both reactions are carried out in a two-phase system of chloroform and water,and halogenated products can be obtained with moderate to good yields.Substrate expansion experiments have shown that coumarins with strong electron donating groups can react with higher yields to obtain halogenated products.The yields of the gram scale experiments are good,confirming the potential production application value of these two reactions.The mechanism of the reactions is speculated through free radical inhibition experiments.This kind of reaction does not need to add transition metal catalysts and additional oxidants.The reaction conditions are mild,and the operation is simple,which meets the requirements of green chemistry.In the third part,α,β-Unsaturated esters are used as raw materials.Sodium chloride and sodium bromide are used as halogen sources.The dibromination and dichlorination reactions are studied under electrochemical conditions.Under the optimal reaction conditions,both reactions are carried out in a two-phase system of chloroform and water,and the dihalide products are obtained with good yields.Specifically,the dibromination reaction does not require the addition of additional electrolytes.Substrate expansion experiments show that the dibromination reaction has good functional group tolerance,and all substrates can converted into target products with excellent yields.However,the chlorination reaction has poor regioselectivity and many by-products.Gram scale experiment has confirmed that the dibromination method has significant advantages in terms of production practicality.The mechanism of the reactions was speculated through free radical inhibition experiments.This type of reaction does not require the addition of transition metal catalysts and additional oxidants.It has the advantages of mild reaction conditions and easy operation.