Construction Of Axially And Plannar Chiral Compounds By Transition Metal Catalyzed Ring Opening Reactions

Chirality is a phenomenon of natural molecules,which includes:helical chirality,axial chirality,central chirality and planar chirality.Ring opening reaction,as a more extensive and effective method to construct chiral compounds,is often accompanied by the breaking process of C-X(X=C,Si,S,N,O,I)bonds.Because of the thermodynamic stability of C-X bond,the ring-opening reactivity is considerably accelerated by using small molecular rings with high bond strain.For another,the process is realized by increasing the ring torsional strain and adding auxiliary groups.This dissertation mainly focuses on the asymmetric ring-opening reactions of fivememebered cycles catalyzed by transition metals.The work can be divided into the following three parts:The first part expatiated a palladium-catalyzed carbon-carbon bond cleavage reaction to build planar chiral diaryl ketones.(1)An acid-mediated chirality inversion of tertiary alcohols(α-hydroxyl group to β-hydroxyl group)was developed.Optically active tertiary alcohols and aryl bromides undergo β-carbon elimination reaction under the presence of palladium and TADDOL skeleton ligands to synthesize planar chiral derivatives.Generally,the reactions showed excellent reactivity and even with 98-99%enantioselectivity.(2)There is also a kinetic resolution process in the ring-opening reaction,and the racemic tertiary alcohol molecule substituted by 2-naphthyl can obtain the highest S value.(3)The preparation of optically active phosphine ligands demonstrates the practicality of this method.The second part describes copper-catalyzed enantioselective ring-opening of biaryliodonium salts with 4-aryl-1H-1,2,3-triazoles.Under the catalysis of copper salts and oxazoline ligands,4-aryl-1H-1,2,3-triazoles with biaryliodonium salts was under a C-N coupling reaction to synthesize a series of axis chiral compounds.This reaction yields 79-99%enantioselectivity as well as excellent regioselectivity with good substrates tolerance.The potential of this series of products for asymmetric catalysis was demonstrated by the preparation of axially chiral phosphine ligands containing triazole structures,where hydrogen abstraction between triazole and aryllithium was observed and the process was controlled by stereic hindrance.The third part reports the design and synthesis of fluorenone helicene and silane helicene.At present,the synthesis of dibromo-substituted biaryliodonium salts and the optimal conditions for the construction of 2,2’-diiodio-6,6’-dibromo biphenyl have been achieved with 91%yield and 96%ee value.Though the ring-opening reaction has good yield and enantioselectivity,the synthesis and application of helical molecules remains to be studied.In conclusion,we realize the synthesis of planar and axial chiral compounds by transition metal-catalytic ring opening reaction.