N-heterocyclic Carbene (NHC) Catalyzed Asymmetric Cycloaddition Of γ-Halo Enal

In recent years,organocatalysis by N-heterocyclic carbene(NHC)has been extensively studied.By NHC catalysis,γ-halo enal can be transferred to vinyl enolate intermediate or acyl azolium intermediate,which can undergo the corresponding [4+x] or [3+x] cycloaddition reactions.This thesis mainly focues on the investigation of NHC-catalytic asymmetric [4+2] and [3+3] cycloaddition of γ-halo enal,providing 3’-spirocyclic oxindoles and N-hydropyridinones.In this thesis,the research work is divided into three chapters.Firstly,a brief introduction on the development of cycloaddition reactions of four intermediates formed by NHC organocatalysis.Chapter 2 describes NHC-catalyzed [4+2] cycloaddition reactions for the synthesis of 3’-spirocyclic oxindoles via C-F bond cleavage protocol.Vinyl enolate intermediate was formed and underwent [4+2] cycloaddition reaction with N-Trt isatin.DFT calculation was carried out and showed that the energy barrier of C-F bond cleavage was as low as 10.8 Kcal/mol activated by NHC.Chapter 3 presents chiral N-heterocyclic cabene catalytic [3+3] cycloaddition reaction of γ-halo enal providing N-hydropyridinone derivatives.The formed acyl azolium intermediate underwent [3+3] cycloaddition with imine in high yields and excellent enantioselectivities.