Asymmetric epoxidation of terminal alkenes with hydrogen peroxide catalyzed by pentafluorophenyl PtII complexes

Easily accessible chiral PtII complexes 1 allow highly enantioselective and completely regioselective asymmetric epoxidation of terminal alkenes with hydrogen peroxide     

双金属催化剂体系催化过氧化氢分解反应

研究了双金属催化剂体系催化过氧化氢分解反应,测量了不同催化剂体系的活化能.结果表明,双金属催化剂对过氧化氢分解反应具有良好的催化性能,且双金属催化剂存在协同催化作用;而酸性环境对过氧化氢催化分解有明显的抑制作用.     

Asymmetric [3 + 2] annulations catalyzed by a planar-chiral derivative of DMAP

A planar-chiral DMAP derivative catalyzes an intriguing [3 + 2] annulation reaction of silylated indenes to produce diquinanes that bear three contiguous stereocenters (one quaternary and two tertiary).     

Flow-injection analysis of hydrogen peroxide based on carbon nanospheres catalyzed hydrogen carbonate-hydrogen peroxide chemiluminescent reaction

A flow-injection chemiluminescence (CL) system with high sensitivity, selectivity, rapidity, and reproducibility is proposed for the determination of hydrogen peroxide (H(2)O(2)) in water samples. The system is based on the reaction of hydrogen peroxide and hydrogen carbonate solution. Carbon nanospheres (CNSs) prepared from aqueous glucose solution are used to enhance the weak CL. The CL intensity was found to be directly proportional to the concentration of H(2)O(2) present in the sample solutions. The effects upon the CL of several physicochemical parameters, including the concentration of the reagents, the mixing order of the reagents, flow rate, pH, particle size of CNSs and other relevant variables, were studied and optimized. The proposed method exhibited advantages in a larger linear range of 5.0 × 10(-8) to 3.0 × 10(-6) mol L(-1) and a lower limit of detection of 1.0 × 10(-9) mol L(-1) (S/N = 3). This method has been successfully applied to the evaluation of H(2)O(2) in tap water and snow water with recoveries from 80 to 110%. The relative standard deviation (RSD) was less than 8% for intra- and inter-assay precision. Based on the kinetic curve, the CL spectrum, fluorescence spectrum, UV-visible spectrum, and electron spin resonance (ESR) spectrum of NaHCO(3)-H(2)O(2)-CNSs system, a possible CL mechanism was proposed. Superoxide ion radical (˙O(2)(-)) and hydroxide radical (˙OH) were generated during the reaction of NaHCO(3) and H(2)O(2). They were the key intermediates for the production of hole-injected and electron-injected CNSs in the CL process.     

Oxidation of caffeine with hydrogen peroxide catalyzed by metalloporphyrins

The biomimetic oxidation of caffeine with hydrogen peroxide using metalloporphyrins as catalysts, which are known to be good biomimetic models of cytochrome P450 enzymes, is investigated. The two manganese porphyrins tested, chloro[5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(III), [Mn(TDCPP)Cl], and chloro [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]manganese(III), [Mn(TPFPP)Cl], afford high conversions of caffeine for all substrate/catalyst molar ratios. Selectivity was found to be dependent on the catalyst employed, and a new spiro racemic compound is described and fully characterized in the solid state from X-ray diffraction studies.     

Epoxidation of propylene with hydrogen peroxide catalyzed by heteropolyphosphatotungstate

The epoxidation of propylene with hydrogen peroxide catalyzed by a reaction-controlled phase transfer catalyst (RCPT) composed of quaternary ammonium heteropolyoxotungstates in acetonitrile medium is studied. The influence of several factors on the reaction is studied, such as the reaction temperature, the effect of H₂O amount, the reaction time, the effect of the catalyst amount, solvent effect and the recycle of the catalyst. Under mild conditions, H₂O₂ conversion is 98.6%, and propylene oxide (PO) selectivity based on H₂O₂ is 97.2%. During the epoxidation, the catalyst is dissolved in the solution. However, after H₂O₂ is used up, the catalyst can be recovered as a precipitate and can be recycled. We find that the recycled catalyst has similar catalytic activity as the fresh one.     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-palygorskite

Palygorskite-supported Sn complexes were prepared by a simple procedure. Cyclic ketones and acyclic ketones were oxidized by hydrogen peroxide in a reaction catalyzed by palygorskite-supported Sn complexes, affording corresponding lactones or esters with selectivity for the product of 90-100%. The catalysts can be recycled for several times without significant decline in catalytic activity.     

Asymmetric Mannich reaction catalyzed by N-arylsulfonyl-l-proline amides

Proline-derived N-sulfonylcarboxamides efficiently catalyze the asymmetric Mannich reaction of cyclic ketones with N-(p-methoxyphenyl)-protected iminoglyoxylate. Both classical organic solvents and ionic liquids were used as the reaction media. With cyclohexanone, the reaction proceeded with high enantioselectivity (99% ee). Enamine intermediates were investigated by DFT calculations.     

手性环状二胺催化的不对称Diels-Alder反应

研究了一种结构新颖、合成路线简单的手性二胺催化的Diels-Alder反应,考察了各种Br nsted酸助催化剂、温度、溶剂和手性二胺分子中不同的取代基对反应的影响.研究结果表明:该类催化剂在催化Diels-Alder反应中表现出较高的催化活性和中等的立体选择性.     

Asymmetric Diels-Alder reaction catalyzed by chiral bases

Anthrone has been found to react with N-methyl maleimide in the presence of catalytic amounts of various chiral β-amino alcohols. The optically active cycloadduct 3a has been obtained in excellent yield. Several features of the reaction have been studied.     

Asymmetric benzoin reaction catalyzed by benzoylformate decarboxylase

Aromatic aldehydes are converted into benzoins by benzoylformate decarboxylase catalyzed C–C bond formation. The reaction affords (R)-benzoins with high enantiomeric excess and in good chemical yields. A broad range of aromatic aldehydes can be used as substrates in aqueous buffer or buffer/DMSO-solutions.     

Epoxidation of olefins with hydrogen peroxide catalyzed by a reusable lacunary-type phosphotungstate catalyst

Olefins and allylic alcohols have been epoxidized with commercially available hydrogen peroxide (30% H2O2) using a phase transfer catalyst,composed of cetyltrimethylammonium cations and a lacunary-type phosphotungstate anion [PW11O39]7-or the complete Keggin-type heteropolyanion [PW12O40]3-,under two-phase conditions using ethyl acetate as the solvent. It was found that the lacunary-type catalyst showed higher activity and better recyclability than the complete Keggin-type catalyst under the same reaction c...     

Enantioselective Staudinger synthesis of beta-lactams catalyzed by a planar-chiral nucleophile

The development of efficient methods for the stereoselective generation of beta-lactams is an important goal, due to their biological activity and their utility as synthetic intermediates. The Staudinger reaction, an overall [2 + 2] cycloaddition of a ketene with an imine, provides a nicely convergent route to this family of compounds. Nearly all studies to date of asymmetric variants of the Staudinger reaction have focused on the use of chiral auxiliaries to control the stereochemistry of the beta-lactam. In this report, we establish that a planar-chiral derivative of 4-(pyrrolidino)pyridine serves as a very effective enantioselective catalyst for the Staudinger beta-lactam synthesis, coupling a range of symmetrical and unsymmetrical ketenes with an array of imines with very good stereoselection and yield.     

Efficient epoxidation reaction of terminal olefins with hydrogen peroxide catalyzed by an iron (II) complex

A highly active iron (II) complex that catalyzed epoxidation of terminal olefins with hydrogen peroxide was described. The catalytic system displayed excellent catalytic ability for the selective oxidation of terminal olefins to epoxides with high selectivity (up to 97.8%) in CH₃CN at 25?°C. The catalytic activity of three similarly structural iron (II) complexes was comparatively studied. The effect of various auxiliary ligands on epoxidation was investigated in detail.     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-aniline complex

Sn-aniline complex was prepared by a simple procedure.Cyclic and acyclic ketones were oxidized into lactones or esters with very high selectivity and yield with 30% hydrogen peroxide in the presence of Sn-aniline complex.     

Asymmetric henry reaction catalyzed by chiral schiff base

Four chiral Schiff bases were synthesized conveniently from chiral amino alcohol and 2-hydroxynaphthalene-1-carbaldehyde. These ligands were used to catalyze the addition of nitroalkanes to aldehydes under ambient conditions in good yields with up to 91% ee.     

Asymmetric ene reaction catalyzed by chiral organoaluminum reagent

The asymmetric ene reaction of prochiral aldehydes with alkenes has been effected by chiral organoaluminum reagent providing optically active homoallylic alcohols in both enantiomeric forms with high enantiomeric purity.     

奎宁-杂多酸杂化催化剂催化H2O2为氧源的苯羟基化反应

将奎宁与Keggin结构磷钼钒杂多酸结合制备出一种新颖的多相苯羟基化杂化催化剂, 采用傅里叶变换红外光谱、紫外-可见光谱、X射线衍射、扫描电镜、热重、N₂吸附-脱附和CHN元素分析等表征手段对催化剂进行了分析. 结果表明, 该催化剂是一种具有较高比表面积和孔体积的半无定形有机杂多酸盐. 在H₂O₂为氧源的苯羟基化反应中, 杂化催化剂引导了液-固两相催化体系, 表现出较高催化活性和重复使用稳定性. 催化剂中奎宁与杂多阴离子间的氢键和电子相互作用赋予了其高熔点和难溶性, 而高比表面积和因奎宁而改善的杂多阴离子的氧化还原性是其获得优异催化性能的主要原因. 这为多相苯羟基化反应提供了一种新的且制备便捷的基于多金属氧酸盐的高效催化剂.     

Asymmetric nitroaldol reaction catalyzed by a C2-symmetric bisoxazolidine ligand

A C2-symmetric bisoxazolidine was found to effectively catalyze the asymmetric Henry reaction of aliphatic and aromatic aldehydes. Beta-hydroxy nitroalkanes were produced in up to 99% yield and 95% ee. The bisoxazolidine-catalyzed nitroaldol formation requires relatively short reaction times, proceeds under mild conditions and is applicable to a wide range of substrates including sterically hindered aldehydes.     

Asymmetric aldol-Tishchenko reaction catalyzed by Yb-complexes with basic amino acid-derived ligands

Simple amino acid-derived esters have been identified as promising chiral sources for the ytterbium-catalyzed aldol-Tishchenko reaction of aromatic aldehydes with aliphatic ketones. The 1,3-anti-diols with three stereogenic centers were isolated in excellent yields, complete anti-diastereocontrol and enantioselectivities of up to 50% ee.