N-heterocyclic Carbene-catalyzed Asymmetric Assemblies Of Dihydrocoumarin And Pyranone

N-Heterocyclic Carbenes(NHCs)are the most common and important organocatalysts in reaction.They have played an important role in organocatalytic reactions,acting as nucleophilic reagents,Bronsted base and Lewis base.The reactions catalyzed by NHCs are usually under mild conditions.Furthermore,they could promote some asymmetric syntheses efficiently.In recent years,they have become one of the research hotspots in the fields of organocatalysis.In this thesis,we mainly focus on the construction of dihydrocoumarin under the catalysis of NHCs.The research work includes the following four parts.In the first part,the structures,properties and classification of N-heterocyclic carbenes were introduced.Then,we discussed the development of organic reactions catalyzed by NHCs.On these bases,our research plan and the innovation of this study were presented.Part two introduced an NHC-catalyzed [4+2] cyclization of saturated carboxylic acid with o-quinone methides through in situ activation,which could gave dihydrocoumarins enantioselectively.This approach features high enantioselectivity,ready availability of the inexpensive starting materials,facile assembly,and potential biological significance of the final products.The third part described the enantioselective synthesis of dihydrocoumarins through NHC-catalyzed in situ reaction of o-quinone methides with α,β-unsaturated carboxylic acids bearing ?-H.The advantages of this protocol include ready availability and high stability of raw materials,good yields,high diastereoselectivity and excellent enantioselectivity.An NHC-catalyzed annulations of 2-(benzo[d]oxazol-2-yl)-1-phenylethanone with α,β-unsaturated carboxylic acids through an in situ activation strategy to construct pyranone bearing a benzo[d]oxazole moiety were presented in the fourth part.The advantages of this protocol include ready availability and high stability of raw materials.All of the products were characterized by 1H NMR,13 C NMR,high resolution mass spectrum and IR.Some structures of the synthesized products were confirmed by X-ray diffraction further.