The Application Of Bis(oxazoline) Ligands In Asymmetric Halogenations

Chiral bis(oxazoline)ligands are characterized by their structural diversity,ready availability,excellent chiral induction,and their ability to catalyzed asymmetric reactions by complexation with transition metals.As one of the most important ligands in synthetic research,chiral bis(oxazoline)ligands have been widely used in asymmetric catalytic reactions with high efficiency,such as 1,3-dipolar addition reactions,cyclopropanation reactions,aldol reactions,Diels-Alder reactions,Friedel-Crafts reactions,Michael reactions,Henry reactions,halogenation reactions,and so on.Considering the efficient chiral control of carbonyl functionalized compounds by the chiral bis(oxazoline)ligands-metal complex,detailed studies on the applications of bis(oxazoline)ligands in asymmetric halogenations for two classes of substates containing carbonyl structure were provided in this thesis.Firstly,the enantioselective brominative dearomatization of 2-hydroxy-1-naphthalene ester catalyzed by chiral bis(oxazoline)-copper complexes was developed,and the chiral naphthalenones bearing a bromine-containing quaternary stereogenic center were obtained with good to excellent enantioselectivities(up to 95% ee)in excellent yields(up to 97% yield)within short reaction times.This reaction not only provided a strategy for the synthesis of chiral naphthalenones derivatives which could be used feasibly for further transformations,but also extended the application of chiral bis(oxazoline)ligands in the asymmetric dearomatization halogenation reaction.Secondly,the asymmetric chlorination of pyrazolone derivatives catalyzed by chiral bis(oxazoline)ligand-copper complexes proceeded in high yields and could gave a series of pyrazolone derivatives with chiral chlorine-containing quaternary carbon centers in high enantioselectivity(up to 96% yield,up to 98% ee).The high enantioselectivity of the catalytic system was ascribed to the excellent chiral induction ability of chiral bis(oxazoline)ligands-copper complex to pyrazole ketone derivatives.This reaction enriched the application of chiral bis(oxazoline)ligand-metal complexes in catalytic asymmetric reactions.In summary,we have expanded the application of chiral bis(oxazoline)-copper complexes in the asymmetric halogenations of 2-hydroxy-1-naphthalene ester and 4-substituted pyrazolone,and the synthetic strategies of naphthalenones and pyrazolone derivatives containing a quaternary chiral center were provided,which may have potential application value in the synthesis of bioactive molecules and natural products.Based on the experimental results and the previous work,the catalytic mode and was analyzed and discussed.These results have an important reference value for the asymmetric catalytic reactions involving the chiral bis(oxazoline)ligands-transition metal complex.