Mechanism Study On The Catalytic Conversion Of Diazo Compounds

The synthesis and application of diazonium compounds have been studied since the end of the 19th century.Owing to their reactivity,aliphatic diazonium compounds and aryl diazonium salts are applied broadly in organic synthesis transformation.Aliphatic diazonium compounds have been widely used as precursors of metalcatalyzed carbene transfer reactions over the past years.With the continuous progress of visible light catalysis technology,visible light-promoted conversion of aliphatic diazonium compounds has received extensive attention due to its green and efficient characteristics.Unlike aliphatic diazo compounds,aryl diazonium salts can not only undergo a substitution reaction to remove the N2 group,but also can retain the N2 group to construct hydrazone,azo and polynitrogen-containing heterocyclic compounds that are difficult to be synthesized by other compounds.Although some progress has been made in experiment field,there are some mechanisms and the origin of chemoselectivity during the transformation of diazonium compounds which are not fully understood at this moment.In this thesis,density functional theory(DFT)is used to investigate the detailed mechanism of three transformation reactions involving aliphatic diazonium compounds and aryl diazonium salts.This thesis is mainly divided into five chapters:the first chapter provides a brief background to the background of the the basic knowledge of quantum chemistry,as well as the analytical methods used in the thesis and diazo compounds.From the second to fourth chapter,the photocatalytic multi-component coupling reaction of αaryldiazoesters,the gold-catalyzed Schmidt-type reaction of aryldiazonium salts and the gold-catalyzed trifunctionalization of aryldiazonium salts and alkynes were discussed,respectively.The following parts are the brief descriptions of the contents:In the second chapter,the mechanism and chemoselectivity of the visible lightcatalyzed multi-component coupling reaction of α-aryldiazoesters,amines,carbon dioxide and cyclic ethers are investigated by DFT.The mechanism obtained from DFT calculations reveals that the reaction starts from an electron-deficient carbene species,which could be provided from a diazoester under photocatalysis.The final products are?ependent on the stability of the oxonium intermediate,which is afforded by nucleophilic attack of the corresponding ether onto a carbene species.Energy decomposition analysis based on absolutely localized molecular orbitals shows that polarization and charge transfer is crucial for the stability of different oxonium ions,and this is related to the nucleophilicity of corresponding ethers.Therefore,the strong nucleophilic THF tends to obtain a four-component coupling product.In the third chapter,the mechanism and regioselectivity of the gold-catalyzed Schmidt-type reaction between 1,3-enyne acetate and aryldiazonium salts were investigated by DFT.Mechanistic studies show that the reaction firstly undergoes cationic Au(I)catalyzed Nazarov cyclization of 1,3-enyne acetates to generate cyclopentadienyl acetate.The 1,2-σ migration process determines the regioselectivity of this reaction.The Newman projections analysis show that the 1,2-σ migration of the secondary carbon would release strain and make it easier to obtain the desired cyclopentadienyl acetate intermediate.Two possible pathways for the Schmidt-type reaction of aryldiazonium salts with cyclopentadienyl acetate could happen:acyl transfer promoting rearrangement or nitrogen-insertive expansion.The calculation results show that the reaction through a more dominant acyl migration pathway to achieve the Schmidt-type rearrangement,thereby giving rise to the 2-pyridinone-based cyclic products.In the fourth chapter,the mechanism of the gold-catalyzed trifunctionalization of alkynes,water and aryldiazonium salts was investigated by DFT.Mechanistic studies indicate that aryldiazonium salts oxidize Au(Ⅰ)species to form Au(Ⅲ)species.Activated by the π-acetic Au(Ⅲ)cation,intramolecular cyclization of alkynes to form five-membered epoxy onium ethylene Au(Ⅲ)species.The five-membered epoxy onium vinyl Au(Ⅲ)species are hydrolyzed under alkaline conditions to obtain neutral 2-hydroxyfuran vinyl Au(Ⅲ)species.Subsequently,the azo compound is obtained by nucleophilic addition of another aryldiazonium salt.Finally,the trifunctional alkyne roduct is obtained by intramolecular ring-opening and reductive elimination of Au(Ⅲ).In this work,aryldiazonium salts act as both oxidants and electrophiles,the obtained insights provide a theoretical basis for the bifunctional action of aryldiazonium salts.The fifth chapter of this paper summarizes the reaction mechanism of two types of diazonium compounds and reveals more applications of diazonium compounds.