Transition Metal-Catalyzed Allylic C-H Alkylation Reactions

Transition-metal catalyzed allylic substitution reaction via allylic C-H bond cleavage is undoubtedly an effective bond-forming process,has been a vital synthetic method for the formation of new carbon-carbon and carbon-heteroatom bonds.?-Allyl metal complex generated by allylic C-H bond activation allows versatile transformations,furnishing chiral compounds with high levels of regioselectivity and enantioselectivity.Compared with traditional transformations starting from prefunctionalized substrates,this strategy using abundantly accessible olefin as substrates provides more step-economical transformations.This thesis mainly describes palladium and platinum catalyzed enantioselective and regioselective allylic alkylation reactions using ?-alkenes as allylating reagents.A highly efficient and general allylic C-H alkylation reaction of terminal alkenes proceeding under mild conditions has been established by palladium-phosphoramidite catalysis.Meanwhile,the chiral phosphoramidite ligand is able to significantly enhance the catalytic activity of palladium complex and to accelerate the allylic C-H alkylation process,providing a successful approach for the creation of asymmetric allylic C-H functionalization of inactivated terminal alkenes with pyrazol-5-ones.Mechanistic studies suggest that allylic C-H activation is conducted through a concerted proton and two-electron transfer process.Besides,a palladium/chiral phosphoramidite complex-catalyzed asymmetric allylic C-H alkylation of 1,4-dienes with cyclic ?-keto esters has been established to afford chiral ?,?-disubstituted ?-keto esters in good to excellent yields,with high levels of regioselectivity and enantioselectivity.Preliminary application of this method enables a concise formal synthesis of(-)-tanikolide.Then,branched selectivity in asymmetric allylic C-H alkylation is enabled by using acylimidazoles as nucleophiles in the presence of a chiral phosphoramidite-palladium catalyst.A wide range of terminal alkenes,including 1,4-dienes and allylarenes,are nicely tolerated and provide chiral acylimidazoles in moderate to high yields and with high levels of region-,and enantio-,and E/Z-selectivities.Mechanistic studies using density-functional theory calculations reveal a nucleophile-coordination-enabled inner-sphere attack mode for the enantioselective carbon-carbon bond-forming event.Furthermore,a Pt-catalyzed allylic C-H alkylation of a wide range of ?-alkenes by using phosphoramidite as ligand and malononitriles as alkylating agents was disclosed.Notably,the combination of chiral urea-catalyzed Michael addition and Pt-catalyzed allylic C-H alkylation can serve as an efficient protocol to access chiral tetrahydropyran with high levels of diastereo-and enantioselectivity.Mechanistic studies suggest that Pt-catalyzed allylic C-H activation occurs through a concerted proton and two-electron transfer process,in analogy to the palladium catalysis in terms of geometry of the transition state.