The enantioselective addition of trimethylsilyl cyanide to a variety of aldehydes proceeded by the aid of a catalyst prepared in situ from titanium tetraisopropoxide [Ti(O-i-Pr)4] and chiral Schiff bases and gave the corresponding cyanohydrins in high optical yield (up to 96% e.e.). A remarkable rate enhancement was brought about by the addition of the Schiffbase to the titanium alkoxide mediated
Direct and Post-Synthesis Incorporation of Chiral Metallosalen Catalysts into Metal-Organic Frameworks for Asymmetric Organic Transformations
作者:Weiqin Xi、Yan Liu、Qingchun Xia、Zijian Li、Yong Cui
DOI:10.1002/chem.201501486
日期:2015.9.1
Two chiral porous metal–organic frameworks (MOFs) were constructed from [VO(salen)]‐derived dicarboxylate and dipyridine bridging ligands. After oxidation of VIV to VV, they were found to be highly effective, recyclable, and reusable heterogeneous catalysts for the asymmetric cyanosilylation of aldehydes with up to 95 % ee. Solvent‐assisted linker exchange (SALE) treatment of the pillared‐layer MOF
the synergistic catalytic effects and associated catalytic mechanisms. In this study, two pairs of chiral lanthanide–transition metal clusters (R)/(S)-Co3Ln2 (Ln = Tb or Dy) were synthesized using Schiff-base ligands [(R)- or (S)-H3L] with multiple Lewis base sites (O sites). The as-prepared (R)/(S)-Co3Ln2 chiral metal clusters exhibited good catalytic functionality in the asymmetric synthesis of chiral
具有明确晶体结构的金属簇对于研究协同催化效应和相关催化机制非常有用。在这项研究中,使用席夫碱配体 [( R )- 或 ( S )-H合成了两对手性镧系元素-过渡金属簇( R )/( S )-Co 3 Ln 2 (Ln = Tb 或 Dy) 3 L]具有多个路易斯碱基位点(O位点)。所制备的( R )/( S )-Co 3 Ln 2手性金属簇在手性氰醇的不对称合成中表现出良好的催化功能,具有高达 99% 的高转化率和高达 78% 的中高对映体过量值。催化过程遵循( R )/( S )-Co 3 Ln 2的双功能金属簇的机理。,含有路易斯酸位点和路易斯碱位点,分别同时活化醛和三甲基甲硅烷基氰化物。因此,实现了协同催化。不同醛的对映选择性和所得产物的立体化学构型归因于通过簇上的外部手性配体形成空间手性口袋。此外,使用( R )/( S )-Co 3 Ln 2手性金属簇进行的多相不对称氰基化反应在
Enantioselective trimethylsilylcyanation of some aldehydes promoted by modified sharpless catalyst
作者:Masahiko Hayashi、Tohru Matsuda、Nobuki Oguni
DOI:10.1039/c39900001364
日期:——
A highly enantioselective method for trimethylsilylcyanation of a variety of aldehydes was developed using a modifiedSharpless reagent.
Chiral Covalent Organic Frameworks with High Chemical Stability for Heterogeneous Asymmetric Catalysis
作者:Xing Han、Qingchun Xia、Jinjing Huang、Yan Liu、Chunxia Tan、Yong Cui
DOI:10.1021/jacs.7b04008
日期:2017.6.28
Covalent organic frameworks (COFs) featuring chirality, stability, and function are of both fundamental and practical interest, but are yet challenging to achieve. Here we reported the metal-directed synthesis of two chiral COFs (CCOFs) by imine-condensations of enantiopure 1,2-diaminocyclohexane with C3-symmetric trisalicylaldehydes having one or zero 3-tert-butyl group. Powder X-ray diffraction and
具有手性、稳定性和功能的共价有机框架 (COF) 具有基本和实际意义,但实现起来仍具有挑战性。在这里,我们报道了通过对映纯 1,2-二氨基环己烷与具有一个或零个 3-叔丁基的 C3 对称三水杨醛的亚胺缩合,金属定向合成两种手性 COF(CCOF)。粉末 X 射线衍射和建模研究以及孔径分布分析表明,基于 Zn(salen) 的 CCOF 具有 AA 堆叠的二维六边形网格网络。与非烷基化类似物相比,在孔壁上掺入叔丁基的 COF 对酸性 (1 M HCl) 和碱性 (9 M NaOH) 条件的化学稳定性显着增强。CCOF 中的 Zn(salen) 模块允许通过合成后金属交换将多元金属安装到框架中。交换后的 CCOF 保持高结晶度和孔隙率,可作为高效且可回收的多相催化剂,用于醛的不对称氰化、Diels-Alder 反应、烯烃环氧化、环氧化物开环和相关的连续反应,ee 高达 97%。