Studies On Base-Metal-Catalyzed Asymmetric Hydroboration Of Alkenes And Sequential Nazarov Cyclizations

Chiral compounds are widely used in pharmaceutials,fine chemicals,materials science and many other fields.Among them,chiral organoboron compounds and chiral cyclopentenone compounds play important roles in organic synthesis.Transition metal catalyzed asymmetric reaction is one of the most efficient methods for the synthesis of chiral compounds.However,most of the central metals of the currently high-efficiency catalysts are noble metals,such as ruthenium,rhodium,palladium and iridium.These noble metals are not only rare in storage and expensive,but also highly toxic to humans.Base metals,such as iron,cobalt and nickel,have been considered as the most ideal alternatives for noble metals in the field of catalysis due to their advantages of abundant sources and good biocompatibility.In recent years,although some advances have been made in base metal-catalyzed asymmetric synthesis,the types of chiral ligands suitable for base metals and efficient catalytic reactions are still relatively limited.This dissertation mainly focuses on the design and synt:hesis of novel chiral ligands to achieve the base-metal-catalyzed highly enantioselective hydroboration of challenging olefins and the development of novel base-metal-catalyzed asymmetric sequential Nazarov reactions.As shown in the following parts:Part I:Studies on dual-stereocontrol asymmetric cobalt-catalyzed hydroboration of sterically hindered styrenes.A more flexible novel oxazolidine aminoisopropylpyridine(OAP)ligand was designed and synthesized from modification of oxazolidine iminopyridine(OIP)ligand.Using OAP ligands,we achieved a highly enantioselective cobalt-catalyzed hydroboration of ortho-substituted sterically hindered styrenes.Meanwhile,a dual-stereocontrol reaction was realized when combined with the OIP cobalt catalysis.In addition,based on the control experiments and the deuterium experiments,we also proposed the possible mechanism and the intermediate models.Part ?:Studies on nickel-catalyzed enantioselective sequential Nazarov cyclization/decarboxylation.Using OIP ligands,we developed a nickel-catalyzed asymmetric sequential Nazarov cyclization/decarboxylation,providing decarboxylated chiral cyclopentenone compounds with excellent yield and enantioselectivity.Mechanistic studies indicated that the reaction undergoes a nickel-catalyzed Nazarov cyclization,followed by nickel-promoted decarboxylationPart ?:Studies on nickel/copper dual catalysis for sequential Nazarov cyclization/decarboxylative aldol reaction.Using aldehydes as electrophile,we continued to develop a nickel/copper dual-catalyzed sequential Nazarov cyclization/decarboxylative aldol reaction,giving the cyclopentenone products with good yields and diastereoselectivities.Preliminary attempts for the enantioselective transformation were tested by using chiral ligands.Part ?;Studies on enantioselective cobalt-catalyzed sequential Nazarov cyclization/fluorination.We synthesized a novel thiazoline iminopyridine(TIP)ligand by replacing the oxazoline ring of the OIP ligand with a more electron-rich thiazoline ring.Using NFSI as a fluorinated reagent,we reported a TIP cobalt complex catalyzed asymmetric sequential Nazarov cyclization/fluorination,constructing a-fluorinated cyclopentenone compound containing chiral carbon-fluorine quaternary stereocenter in one-step.Part ?:Experimental section.The general procedures for the preparation of starting materials,experiments and characterization of compounds in this dissertation were described.