Pd(Ⅱ)-Catalyzed Alkenes Enantioselective C-H Olefination Reactions

Conjugated diene fragments are widespread in drug molecules,natural products and organic functional materials.Compared with olefin,conjugated diene,as an important organic synthesis intermediate,has unique chemical properties and reactivities.Therefore,how to effectively construct the functionalized conjugated dienes is one of the research hot topics in organic synthesis.Transition metal catalyzed oxidative cross-coupling of olefin is one of the ideal and atom-economical approaches to prepare conjugated dienes.In this dissertation,we have synthesized axially chiral styrene derivatives with highly optical activity and chiral amine compounds containing 1,3-conjugated diene fragments by Pd(Ⅱ)-catalyzed asymmetric oxidative coupling of alkenes.The research contens are as follows:Part Ⅰ:Palladium-Catalyzed Synthesis of Atropisomeric Styrene Derivatives via C-H Bond Activation of AlkenesWe have developed a Pd(Ⅱ)-catalyzed asymmetric oxidative coupling reaction of styrene derivatives with electron-deficient alkenes to prepare axially chiral styrene derivatives with highly optical activity.The rotation of single bond between the alkenyl and aryl groups was prevented by increasing the steric hindrance of the substituents on olefins.In this reaction,the commercially available PyBox was used as ligand under mild and simple reaction conditions.A gram-scaled reaction was also performed smoothly to give the desired product in good yield.The kinetics studies suggest that the alkene C-H bond cleavage is the possible rate-determining step.Part Ⅱ:Palladium-Catalyzed Stereospecific and Enantioselective C-H Bond Olefination Reaction of Alkenes via Kinetic ResolutionWe have developed a Pd(Ⅱ)-catalyzed oxidative cross-coupling reaction of homoallylamines with electron-deficient alkenes.In this reaction,the alkenyl C-H bond of homoallylamine compounds was activated by palladium catalyst and then reacted with the electron-deficient olefins to construct the highly stereoselective conjugated diene fragments.First,the racemic target products can be prepared in high yields and with good stereoselectivities under mild reaction conditions by using glycine derivative as ligand.When a serine derivative was used as chiral ligand to combine with palladium catalyst,the chiral amine compounds containing 1,3-conjugated diene fragments can be prepared through kinetic resolution.The kinetics studies suggest that the alkenyl C-H bond cleavage is the possible rate-determining step.Part Ⅲ:Palladium-Catalyzed Stereospecific and Enantioselective C-H Bond Olefination Reaction of Alkenes via DesymmetrizationWe have developed a Pd(Ⅱ)-catalyzed asymmetric cross-coupling reaction of homoallylamine derivatives with electron-deficient alkenes.In the presence of leucine derivative as chiral ligand to combine with palladium catalyst,the desired chiral amine compounds containing 1,3-conjugated diene fragments were obtained via a desymmetric strategy.Currently,the enantioselectivity of the desired coupling product is excellent albeilt with a low yield.Therefore,the study on improving the product’s yield is still on the way at our laborotory.