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

开发一种有效的手性控制催化不对称反应的方法是21世纪合成有机化学领域的中心课题之一。在目前的研究中，我们面临着设计和合成基于李钢骨架构象控制和屏蔽取代基的高效手性催化剂的挑战。一种是反式螯合的三齿手性配体，具有二苯并呋喃骨架，在4位和6位有两个恶唑啉取代基。另一种是通常的双草碱型手性配体，具有邻羟基部分的苄基屏蔽取代基。这些配合物在强配位亲核催化的不对称反应中被有效利用。硝基环加成：R，R- dbfox /Ph配体的镍（II）水络合物在室温下以2mol %的催化负荷成功催化硝基环加成成3-克罗丁酰-2-恶唑烷酮及其衍生物，表现出极高的非映对和对映选择性。使用单齿亲极试剂进行硝基环加成反应：使用溴丙烯醛作为单齿亲极试剂，在R，R- dbfox /Ph配体的锌（II）配合物存在下，硝基环加成反应进行得更有效。已有证据表明，该反应是通过硝酮/催化剂/受体活化络合物的内部递送机制进行的。重氮环加成反应：在R，R- dbfox /Ph配体（10 mol%）的锌（II）配合物存在下，三甲基硅基重氮甲烷与3-crotonoyl-2-恶唑烷酮及其衍生物之间的重氮环加成反应具有优异的对映选择性。另一方面，3-巴豆酰-4,4-二甲基-2-恶唑烷酮的类似反应完全不能被锌（II）和镍（II）配合物激活，而只能被镁配合物激活。具有相反模式的高对映选择性。氨基共轭加成：R，R- box /o-HOBn配体的铜（II）配合物在o-苄基羟胺与3-异丙基-1-克罗托酰-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。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