| Pyridine and its derivatives,as an important class of heterocyclic compounds,with high stability and good coordination ability with most metals,have attracted wide attention in the fields of organic chemistry,material chemistry and supramolecular chemistry.Chiral ligands are the key structural components for tuning the activity and stereoselectivity of metal catalysts in enantioselective transformations.Pyridine is undoubtedly the most widely used structural units of ligands in homogeneous catalysis.However,development of the asymmetric versions of these catalytic reactions have been significantly limited because the lack of highly efficient of the chiral pyridine skeleton as the ligands for asymmetric catalysis.The major problems for this gap include the difficulty to introduce chiral elements for a planar structure,local substituents’steric hindrance induced paradox between activity and stereoselectivity,the poor flexibility in structural modification and the challenges for modular synthesis.Therefore,exploring an effective and universal chiral pyridine ligand skeleton is still a bottleneck problem in the field of asymmetric catalysis.This thesis aims to design and synthesize a brand-new rigid fused ring backbone which is easy to modify,and provide a new method for the preparation of chiral ligands.We have synthesized a series of chiral pyridine-derived N,B-bidentate ligands,their activity and enantioselectivity of the new ligands were evaluated by the enantioselective Ir-catalyzed directed arene C-H borylation reaction,which is still lack of effective asymmetric synthesis.The main research results are summarized as follows:The first chapter of this thesis summarizes the research background and application potential of chiral pyridine ligands detailedly,especially the preparation methods and homogeneous catalysis applications of chiral pyridine ligands.In the second chapter,the synthetic route of chiral chloropyridine with tricyclic fused backbond is studied.Using commercially available 2-cyclopenten-1-one as starting material,a chiral chloropyridine half-molecule with a[5,3]bicyclic backbond was prepared through 7-step reactions.Starting from simple and easily available 2-cyclopenten-l-one,bromination reaction at α position of the carbonyl group,generating the compound of bromination;The cyclopropanation reaction can be used after bromination to prepare racemic fused ring ketone;Optical resolution of the cycloketone can be obtained by using cheap and easily available Ellman’s N-tert-butyl sulfoximine chiral auxiliary,leading to the optically pure fused cyclic ketone;Then convert the chiral ketone obtained by hydrolysis to corresponding ketoxime readily,and the enamide compound was obtained by reducing the ketoxime in the presence of iron powder;Finally,using Vilsmeier-Haack reaction(DMF,POCl3,80℃)can successfully generate the chloropyridine derivative;The chiral chloropyridine derivative can be prepared via three steps from the chiral ketone.In addition,conditions optimization of each step in the synthetic route were carried out,so that each step could be conducted in decagram or gram scales(up to 12 g),and the yield was stable between 80%and 90%.The third chapter discusses the preparation of chiral pyridine-derived N,B-bidentate ligand and its application in asymmetric homogeneous reaction.The ligands PL-1,PL-2,PL-3,PL-4,PL-5,PL-6 and PL-7 were successfully prepared,and their application in enantioselective Ir-catalyzed directed arene C-H borylation reaction was evaluated with 87%yield and 66%enantionmeric excesses.It demonstrated that this kind of novel backbone chiral pyridine ligands have full potential application value in the field of asymmetric organic synthesis.The fourth chapter summarizes and prospects the research work of this paper.The fulfillment of this research provides universal innovative ideas and new framework chiral ligands for the development of asymmetric catalysis,and provides new methods toward the preparation of chiral molecules. |
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