Study On Asymmetric Cycloaddition Reactions Of α,β-Unsaturated Esters Catalyzed By N-Heterocyclic Carbenes

N-Heterocyclic carbenes(NHCs) serve as excellent ligands in organometallic catalysis have been widely studied. Over the last decade, N-heterocyclic carbenes(NHCs) can also act as organocatalysts opening up a new avenue for the synthesis of target molecules. For instance, the traditional a1-d1umpolung(benzoin condensation6 and Stetter reaction7) and a3-d3 umpolung(homoenolate cycloaddition8) approaches have been well-documented. In particular,(oxidative) NHC organo-catalysis has been extended to α-carbon, β-carbon and γ-carbon activition. This thesis manly focuses on the the investigstion of NHCs as organocatalysis in cycloaddition reactions, achieving new synthetic strategies.In this thesis, the research work is divided into three chapters. Firstly, a brief introduction on the NHCs history and the development of NHC-catalytic reactions including homoenolate intermediates, enolate species and vinyl enolate intermediate is presented in chapter 1.Chapter 2 describes chiral NHC-catalytic [3+3] cycloaddition reactions of???-unsaturated esters to imines, affording six-membered lactams in good yields and high enantioselectivities.Chapter 3 presents chiral NHC-catalyzed formal [4+2] cycloaddition reactions of???-unsaturated esters to istain derivatives, affording six-membered lactone in moderate yields and enantioselectivities.All the obtained products were characterized by1 H NMR,13 C NMR and high HRMS. The enantioselective exess was determined by HPLC analysis on chiralpak or column.