[3+3]Cycloaddition Reactions Involving α,β-Unsaturated Acylazoliums

N-heterocyclic carbene(NHC),as a green,safe and stable small molecular catalyst,plays an important role in organic synthesis.Because of its excellent performance and the absence of metal,it is favored in practical applications.NHC can be catalytically activated into various intermediates to participate in organic reactions.The α,β-unsaturated acylazolium intermediates as biselectrophiles,which can undergo cycloaddition reaction with bisnucleophiles to construct a variety of new heterocyclic skeletons.At present,the range of application of nucleophiles(mainly strong nucleophiles such as enylamine and enol)which have cycloaddition reaction with this intermediate is relatively limited,so the search for new nucleophiles has become one of the important development directions in this field.And this will contribute to the development of NHC in the field of organic catalysis and its wider application in more fields.This thesis focused on the [3 + 3] cycloaddition reaction of α,β-unsaturated acylazolium intermediates with various types of strong nucleophiles.This thesis is mainly divided into four parts:In the first part,the development process of NHC and the activation type of NHC catalysis are introduced.Then,a brief overview of the catalytic activation of NHC into α,β-unsaturated acylazolium intermediates and the involvement of asymmetric cycloaddition reactions is given.In the second part,we studied 5-amino-isooxazole as a novel bisnucleophile,which was involved in the cycloaddition reaction of the α,β-unsaturated acylazolium intermediates.A series of isooxazolpyridone derivatives with good yields and high enantioselectivities were efficiently synthesized using chiral NHC pre-catalysts under mild conditions.This reaction achieves the construction of the β-position C-C bond of unsaturated aldehydes and is the first example of direct catalytic asymmetric synthesis of dihydroisoxazolo[5,4-b]pyridin-6-ones.In the third part,we studied the cycloaddition reaction between α-bromo-unsaturated aldehydes and 5-aminopyrazole catalyzed by NHC pre-catalysts,and efficiently synthesized pyrazolpyrimidine derivatives,and realized the construction of β-position C-N bond of unsaturated aldehydes.The reaction conditions are mild and the substrate has wide applicability.It not only provides a simple and convenient method to construct pyrazolpyrimidone skeleton,but also the synthesized compounds have potential application prospect.In the forth part,the [3 + 3] cycloaddition reaction between α-bromo-unsaturated aldehydes and 2-mercaptobenzimidazole was studied,and β-position C-S bond of unsaturated aldehydes was constructed.Aryl substituted α-bromo-unsaturated aldehydes are well tolerated and can synthesize dihydrobenzo[4,5]imidazo[2,1-b][1,3]thiazin-4-ones with good yields.The generated benzimidazolthiazone derivatives can also provide effective strategies for the synthesis of natural products.