Nickel Catalyzed Construction Of ?/?-Aryl/alkenyl C–Glycosides And Migratory Benzylic Alkenylation

This thesis includes two parts:Ni-catalyzed stereodivergent synthesis of aryl/alkenyl C-glycosides and Ni H-catalyzed remote alkenylation of olefins and asymmetric alkenylation.The specific description is illustrated as follows:In the first section,nickel-catalyzed stereoselective synthesis of aryl/alkenyl C-glycoside compounds has been studied.Builidng on the cross-elecrophile coupling strategy,three different reaction conditions have been developed that enabled ligand–controlled stereodivergent synthesis of C-aryl/alkenyl glycoside.The first reaction system employed Ni(Cl O₄)₂·6H₂O as the catalyst,pyridine or DMAP as the ligand,Zn as the reducing agent,and Mg Cl₂as the additive.The reaction afforded?-aryl/alkenyl C-glycoside in high stereoselectivity under mild conditions.The second reaction system employed Ni(Cl O₄)₂·6H₂O as a catalyst,dtb Bpy as a ligand,Zn as a reducing agent,and Mg Cl₂ as additive,affording aryl/alkenyl C-glycoside in high yields and moderate?-steroselectivities.The third system employed Ni(acac)₂as catalyst,t Bu-Terpy as ligand,and Zn as reducing agent furnishing aryl/alkenyl C-glycosides in high?-selectivities under mild reaction conditions.The Ni-catalyzed reductive C–glycoside synthesis exhibited excellent functional group tolerance and broad substrate scope.Finally,a radical–chain mechanism was proposed basd on the reaction of an isolated Ar–Ni ^II intermediate,a radical-clock experiment.In the second section,nickel-catalyzed remote alkenylation of olefins and their asymmetric reactions have been studied.Firstly,Ni H-catalyzed remote alkenylation of olefins was illustrated.The high regioselectivity was achieved using a pre-prepared Ni Br₂·dmdpy complex as a catalyst,HBpin as hydrogen source,Li OMe as base,and DMA as solvent through a one-step reaction.This reaction displayed broad substrate scope and high functional group tolerance.Mechanistic studies implied that the difference in chemoselectivity of olefins was mainly due to the activity of olefins,wherein Ni–H species did not dissociate from the parent olefins during the"chain walking"process.On the basis of this copuling framework,we have also developed a nickel-catalyzed asymmetric alkenylation of styrenes.By using a pre-formed Ni complex as chiral catalyst,HSi(OEt)₃ as hydride source,Cs F as additive,the coupling of styrene compounds and alkenyl bromides delivered the alkenylated products in high yields,and excellent regioselectivities and enantioselectivitiesunder mild conditions.Finally,we have discovered that Me₂S–BH₃ severed as an alternative hydride sourcefor the nickel-catalyzed remote arylation and alkenylation of olefins,which featured high atom economy,less loading,and provided the poducts in excellent regioselectivities.