DESIGN AND SYNTHESIS OF EFFICIENT CHIRAL CATALYSTS BASED ON CONFORMATIONAL CONTROL OF SHIELDING SUBSTITUENT

开发一种有效的催化不对称反应手性控制方法是21世纪合成有机化学领域的中心课题之一。在本研究中，我们面临的挑战是设计和合成基于Ligang骨架构象控制和屏蔽取代基的高效手性催化剂。一种是反式螯合三齿手性配体，它具有二苯并呋喃骨架，在4位和6位分别有两个恶唑啉取代基。另一种是常见的双恶唑啉型手性配体，具有苯基屏蔽取代基和邻羟基取代基。这些配合物被发现有效地用于强配位亲核试剂的催化不对称反应。硝酮环加成反应：在室温下，R，R-DBFOX/Ph配体的镍(II)水合体催化了3-巴豆酰基-2-恶唑烷酮及其衍生物的硝酮环加成反应，显示了Ext…更高的非对映选择性和对映体选择性。使用单齿偶极分子的硝酮环加成反应：在R，R-DBFOX/Ph配体的锌(II)络合物存在下，以溴丙烯醛为单齿偶极分子的硝酮环加成反应效率更高。研究表明，该反应是通过硝酮/催化剂/受体活化络合物的内部传递机制进行的。重氮环加成反应：在R，R-DBFOX/Ph配体的锌(II)络合物存在下，三甲基硅基重氮甲烷与3-巴豆酰基-2-恶唑烷酮及其衍生物的重氮环加成反应具有良好的对映选择性。另一方面，3-巴豆酰基-4，4-二甲基-2-恶唑烷酮的类似反应不能被锌(II)和镍(II)络合物所激活，而被镁络合物所激活。得到了具有相反模式的高对映体选择性。胺共轭加成：R，R-box/o-HOBN配体的铜(II)络合物被发现在O-苄基羟胺与3-异丙基-1-巴豆酰基-2-咪唑烷酮的胺共轭加成反应中非常有用。这种反应也被认为是通过内部传递机制进行的。较少

Development of a useful method of chirality control in catalyzed asymmetric reactions is one of the central subjects in the field of synthetic organic chemistry in 21st century. In the present research, we have challenged to design and synthesize efficient chiral catalysts based on conformational control of ligang skeleton as well as shielding substituents. One is a trans-chelating tridentate chiral ligand which has a dibenzofuran skeleton with two oxazoline substituents at 4- and 6-positions. The other one is a usual bisoxaloline type of chiral ligand having benzyl shielding substituents with o-hydroxyl moiety. These complexes are found to be effectively utilized in the catalyzed asymmetric reactions of strongly coordinating nucleophiles.1. Nitrone Cycloadditions : The nickel(II) aqua complex of R,R-DBFOX/Ph ligand successfully catalyzes the nitrone cycloaddition reactions to 3-crotonoyl-2-oxazolidinone and derivatives in the catalytic loading of 2 mol% at room temperature to show ext … More remely high diastereo- and enantioselectivities.2. Nitrone Cycloadditions Using Monodentate Dipolarophiles : The nitrone cycloaddition reactions using bromoacrolein as a monodentate dipolarophile proceed much more efficiently in the presence of the zinc(II) complexes of R,R-DBFOX/Ph ligand. It has been evidenced that this reaction proceeds through the internal delivery mechanism of the nitrone/catalyst/acceptor activated complex.3. Diazo Cycloadditions : Excellent enantioselectivity has been attained in the diazo cycloaddition reactions between trimethylsilyldiazomethane and 3-crotonoyl-2-oxazolidinone and derivatives in the presence of the zinc(II) complexes of R,R-DBFOX/Ph ligand (10 mol%). On the other hand, similar reactions of 3-crotonoyl-4,4-dimethyl-2-oxazolidinone can be activated not by the zinc(II) and nickel(II) complexes at all but the magnesium complex. The high enantioselectivities with the opposite mode have resulted.4. Amine Conjugate Additions : The copper(II) complex of R,R-BOX/o-HOBn ligand is found to be very useful in the amine conjugate addition reactions of O-benzylhydroxylamine to 3-isopropyl-1-crotonoyl-2-imidazolidinone. This reaction is also believed to proceed through the internal delivery mechanism. Less