Asymmetric [4+2] Cyclization And Cyclopropanation Reactions Catalyzed By Metal-centered Chiral Complexe

Chiral ring skeleton is widely found in the core structure of many natural products and drug molecules.Asymmetric cyclization has always been an important method to construct multicomponent ring systems in organic chemistry.It helps to efficiently synthesize ring skeleton molecules with specific stereoscopic configurations.Therefore,its research is of great significance for the development of new organic synthesis methods.In this thesis,the asymmetric cycloaddition reactions were studied by using rhodium octahedral chiral metal complex as asymmetric chiral catalyst.Chapter 1 is the introduction part which summarizes the general development of chiral-at-metal complexes as asymmetric chiral catalysts,their advantages as chiral Lewis acid catalysts,their reaction mechanisms,and their applications in different types of asymmetric catalytic reactions.In Chapter 2,an efficient asymmetric [4+2] cyclization of α,β-unsaturated 2-acyl imidazoles with ortho-hydroxyphenyl-substituted para-quinone methide derivatives catalyzed by a chiral-at-metal rhodium complex has been developed.Enantioenriched chroman derivatives bearing three contiguous tertiary stereocenters were obtained in generally high yields(up to 97%)and good stereoselectivities(up to >20?:?1 dr,>99%ee).This reaction represents the first catalytic asymmetric [4+2] cyclization of ortho-hydroxyphenyl-substituted p-QMs using chiral Lewis acids as catalysts,which will enrich the field of the catalytic asymmetric reactions of p-QM derivatives.More importantly,it also provides a useful method for constructing chiral chroman skeletons.In Chapter 3,an efficient asymmetric cyclopropanation of sulfoxonium ylides with α,β-unsaturated 2-acyl imidazoles catalyzed by a chiral-at-metal rhodium complex has been developed.The enantioenriched cyclopropane derivatives bearing three contiguous tertiary stereocenters were obtained in generally high yields(up to98%)with excellent stereoselectivities(up to >20?:?1 dr,>99% ee).Remarkably,as low as 0.1 mol% of the chiral Rh(III)complex can realize a scale-up reaction with excellent yield and enantioselectivity.The experimental results show that the reaction products have high yield and good stereoselectivity.It can be seen that this kind of catalyst shows a good application prospect in the study of asymmetric cyclization reaction.Therefore,we hope to use this kind of catalyst to try more new cyclization reaction.The fourth chapter of this thesis is a literature review,which introduces the current research status of asymmetric cyclization reactions based on p-QMs in recent years.It is only used as a supplement for the research materials in the second chapter of this thesis.