Formation of chiral charge-transfer complex with axially chiral 1,1′-bi-2-naphthol and viologen derivatives

By using three types of viologen derivatives, we synthesized chiral charge-transfer (CT) complexes with an axially chiral 1,1′-bi-2-naphthol molecule and successfully controlled the crystal structure and inclusion ability of the third component by changing the viologens.     

Efficient resolution of racemic 1,1'-bi-2-naphthol with chiral selectors identified from a small library

Efficient resolution of racemic 1,1'-bi-2-naphthol, a well-studied analyte in chiral separation, was achieved using selectors developed from a small library. Separation factors (up to 7.2) obtained are significantly higher than the ones reported previously for this analyte. The library consists of 121 members and it does not contain the pi deficient 3,5-dinitrobenzoyl (Dnb) group. These highly efficient stationary phases may lead to the practical large-scale chromatographic resolution of enantiomers of 1,1'-bi-2-naphthol, which are widely used as chiral auxiliaries and ligands in asymmetric synthesis.     

Solvent effect in the chromatographic enantioseparation of 1,1′-bi-2-naphthol on a polysaccharide-based chiral stationary phase

Enantioseparation of 1,1′-bi-2-naphthol (BINOL) was performed on a polysaccharide-based chiral stationary phase, Chiralcel OD-H, under normal-phase mode. The effects of polar modifier in the mobile phase on the retention, enantioseparation and elution order were investigated in detail. Solvent-induced reversal of elution order for BINOL was observed. When linear alcohols were adopted, R-BINOL was always eluted first. S-BINOL was eluted first when 2-propanol was used as a polar modifier. Enantioseparation could not be obtained when sec-butyl alcohol or tert-butyl alcohol was used as a polar modifier. When isoamyl alcohol or cyclohexanol was used as a polar modifier, favorable enantioseparation was obtained as with 1-pentanol or 1-hexanol; also, R-BINOL was the first-eluted enantiomer. It is worth emphasizing that significantly better enantioseparation was obtained when higher alcohols were used as polar modifier of the mobile phase. A nonlinear characteristic for the ln α against 1/T plots was universally observed in this study though the ln k against 1/T plots exhibited a linear feature. Associated with the obtained thermodynamic parameters, some interesting inferences about chiral recognition mechanism were proposed.     

Access to chiral tertiary amines via the iridium-catalyzed asymmetric hydrogenation of enamines

The asymmetric hydrogenation of N,N-dialkyl and N-alkyl-N-aryl enamines to chiral tertiary amines was studied. All the N,P-ligated iridium complexes investigated were active catalysts for the reaction, but only those with bicycle-supported oxazoline-phosphine ligands gave reasonable stereoinduction. The best catalyst produced a range of chiral tertiary amines in up to 87% ee.     

A charge-transfer host system composed of a chiral 1,1′-bi-2-naphthol cluster and benzylviologen

Chiral charge-transfer (CT) complexes composed of a chiral 1,1′-bi-2-naphthol cluster as the electron donor and 1,1′-dibenzyl-4,4′-bipyridinium dichloride as the electron acceptor serve as a host system for molecular recognition. CT complexes that include guest alcohols show different diffuse reflectance spectra (DRS) depending on the included guest.     

Synthesis of macrocyclic 1,1′-biarenol derivatives by the tandem Claisen rearrangement and their binding properties

Crown ether-type macrocycles consisting of an enantiopure biarenol derivative and an oligoethylene glycol were synthesized by the Lewis acid-mediated tandem Claisen rearrangement. This is the first example of the successful application of the tandem Claisen rearrangement to the synthesis of enantiopure macrocyclic biarenol derivatives. The enantiopure macrocyclic biarenols were found to form 1:1 complexes with amino acid salts and to discriminate their chirality.     

醇存在下R,S-1,1′-2-联萘酚对映体的环糊精手性识别研究

以R,S-1,1′-2-联萘酚对映体为手性客体分子, 采用荧光探针法详细研究了各种醇对β-环糊精/(R或S)-1,1′-2-联萘酚对映体的手性包络和手性荧光猝灭等性质的影响, 结果表明, 醇的存在可显著影响R,S-1,1′-2-联萘酚对映体与β-环糊精形成包络物的包络形式和包络常数. 通过与该对映体的β-环糊精手性固定相高效液相色谱拆分法比较研究结果表明, 醇等第三客体分子可显著影响环糊精对对映体化合物的手性选择性和分离度.     

Effect of water on BINOL/Ti(OPr)4 solution mixtures: The nature of a catalytic precursor of enantioselective sulfoxidation

The solution mixtures of (R)-BINOL, Ti(OⁱPr)₄ and H₂O in 1:0.5:10 proportion in CCl₄, corresponding to the conditions employed for catalyzing the enantioselective oxidation of sulfides to sulfoxides, contain a single titanium BINOLate species. NMR, CD and MS characterization allowed us to identify this species as (BINOLate)₆Ti₄(μ₃-OH)₄ with tetrahedric symmetry consistent with a known crystallographic structure. By varying sample preparation conditions, some aspects of the catalytic behavior could be rationalized. Using racemic BINOL, several heterochiral species were observed in accord with reported non-linear effects in catalysis.     

Stereoselective synthesis of chiral tertiary alcohol building blocks via neighbouring group participation from tri-substituted olefins

A regio- and stereoselective preparation of chiral quaternary 1,2/1,3-diols from acyclic tri-substituted alkenes is disclosed. Optically active tertiary alcohols are the constituents of several bioactive natural products, pharmaceuticals and a general method for their preparation is desirable. A sulfinyl moiety has been utilized as an intramolecular nucleophile.     

Ultrasound assisted one-pot synthesis of 1,2-diaryl azaindoles via Pd/C-Cu catalysis: Identification of potential cytotoxic agents

Ultrasound assisted one-pot and direct access to 1,2-diaryl substituted azaindole derivatives has been achieved via the sequential N-arylation followed by coupling-cyclization under Pd/C-Cu catalysis. The methodology involved initial CN bond forming reaction (step 1) between an appropriate o-bromo substituted amino pyridine and iodoarene followed by CC and CN bond formation (step 2) between the resulting N-aryl substituted intermediate and a terminal alkyne in the same pot. A variety of azaindoles was prepared by using this method. These compounds were assessed for their cytotoxic properties against two different metastatic breast cancer cell lines. Compounds 4i, 4k and 4o showed promising growth inhibition of these cell lines and SIRT1 inhibition in vitro.     

One-pot synthesis of CuO/TiO2 nanocomposites for improved photocatalytic hydrogenation of 4-nitrophenol to 4-aminophenol under direct sunlight

The excellent photocatalytic hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with NaBH₄ in the aqueous medium is still a big challenge. Herein, we report a facile one-pot evaporation-induced self-assembly (EISA) method to synthesize a series of CuO/TiO₂ nanocomposites. The as-synthesized CuO/TiO₂ photocatalysts exhibit remarkable catalytic activity under direct sunlight in selective hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) due to the synergistic interaction of guest copper nanoparticles with host titanium dioxide (TiO₂) species. Especially, 5 wt% CuO/TiO₂ nanocomposite revealed superior reaction rate constant (k) value (0.306 min⁻¹) when compared to 3 wt% CuO/TiO₂ (0.192 min⁻¹) and 7 wt% CuO/TiO₂ (0.240 min⁻¹). Moreover, several characterization techniques (XRD, TEM, N₂ adsorption–desorption isotherm, DRS, and XPS) were executed to deeply investigate the effect of copper content on the bulk and interfacial properties of the catalysts. The characterization results proved that the superior photocatalytic hydrogenation over 5 wt% CuO/TiO₂ catalyst can be ascribed to moderate CuO loading as well as even dispersion of CuO species on the surface of active TiO₂ host, which can largely improve the light absorption ability within visible light region. Besides, the 5 wt% CuO/TiO₂ catalyst exhibits remarkable recyclability and durability, retaining its superior activity (above 95%) up to several repeating cycles, proving its practical applicability for hydrogenation reactions at domestic and industrial levels.     

Effects of type of contact between Co/SiO2 and Pd/b on the direct synthesis of isoparaffins from synthesis gas

The effect of addition of Pd/b on the Co/SiO₂ catalyst was studied for F-T reaction. Pd/b could enhance the formation of C₄-C₉ isoparaffins while the Co/SiO₂ catalyst alone gave the products with wide carbon numbers distribution. The reason is the olefins and long-chain normal paraffins from F-T reaction on Co/SiO₂ catalyst form light hydrocarbons containing isoparaffins through the hydrocracking and hydroisomerization on Pd/b. For Co/SiO₂+Pd/b catalyst, the selectivity to isoparaffins depends on the contact conditions. The granular hybrid catalyst is much more selective for isomerization than the powder hybrid catalyst, while the selectivity to CH₄, n-paraffins and olefins is lower than that on the powder hybrid catalyst. This revised version was published online in August 2006 with corrections to the Cover Date.     

Operationally convenient, efficient asymmetric synthesis of enantiomerically pure 4-aminoglutamic acids via methylene dimerization of chiral glycine equivalents with dichloromethane

This paper presents a practical and efficient asymmetric synthesis of enantiomerically pure 4-aminoglutamic acids using a quite unusual methylene dimerization of chiral nucleophilic glycine equivalents with dichloromethane under phase-transfer catalysis (PTC) conditions. From a synthetic standpoint, the reported procedure is highly operationally convenient and scalable as it does not require any chromatographic purification of the intermediate products.     

The green synthesis of 2,3-dihydroquinazolin-4(1H)-ones via direct cyclocondensation reaction under catalyst-free conditions

ABSTRACT

A simple and environmentally benign method is described for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones by direct cyclocondensation of 2-aminobenzamide with aromatic aldehydes using water as the reaction medium. The parameters such as temperature, substrate molar ratio and reaction time were examined to establish the optimal synthetic process. The present procedure has advantages of low cost, mild reaction conditions, simple workup process, simply purification, excellent yields and no use of catalyst and hazardous organic solvents.     

啶酰菌胺的合成研究

本文报道一种啶酰菌胺的新方法,即用Pd(OH)2/C催化的对氯苯硼酸与2-硝基溴苯的Suzuki反应、其产物2-(4-氯苯基)硝基苯经水合肼-三氯化铁体系还原后与2-氯烟酰氯或2-氯烟酸缩合得目标产物。在Suzuki反应中,考察了反应温度、无机碱、季铵盐和溶剂对反应的影响后。再考虑到生产效率与生产成本的因素,发现以K3PO4·7H2O为无机碱,四丁基溴化铵(TBAB)为助剂,在DMF中,120℃下反应13h,Pd(OH)2/C能很好地催化对氯苯硼酸与2-硝基溴苯的Suzuki反应,并在这一的条件下考察Pd(OH)2/C循环利用的情况。     

可控碳改性Pd/TiO2用于直接合成双氧水:非均相界面对催化性能的影响（英文）

双氧水(H2O2)是一种重要的绿色氧化剂,广泛应用于纺织、医疗、废水处理、军事等重要领域.目前, H2O2的工业生产以蒽醌法为主,该法设备投资大、运行成本高,同时工艺涉及大量的有机溶液,活性中间体蒽醌也会发生缓慢降解,产生有毒副产物.与蒽醌法相比,通过负载型贵金属催化剂催化H2与O2反应直接合成H2O2,过程绿色环保且生产工艺简单,引起了各界广泛关注.然而,从热力学上分析, H2和O2更容易反应生成H2O, H2O2只是该反应的中间产物,会继续发生加氢和直接分解反应生成H2O,导致H2和O2的低效利用,开发高H2O2选择性且高反应效率的催化剂已成为氢氧直接合成H2O2研究的重点与难点.目前大部分研究策略旨在通过调控或影响反应中心结构、价态来抑制H2O2的副反应,进而提升H2O2的选择性和反应效率;尽管已取得了良好的进展,但仍需发展新的调控策略来满足工业应用的要求.本课题组前期研究表明,促使H2O2从催化剂上脱附可以有效地提升H2O2的选择性和产率.相比于针对反应中心的调控,不稳定的H2O2从催化剂上快速脱附同样起到抑制H2O2参与副反应的作用.为此,本文提出一种炭量可控的非均一界面改性方法,以常规的Pd/TiO2作为研究对象,借助各种结构表征,发现炭物种在TiO2表面呈非均一分散状态,而且改性对于催化剂的几何结构影响较小;另外,催化剂表面的疏水性会随着碳含量的增加而增加,导致其与H2O2间的吸附能相应变小.反应结果显示,表面非均一的炭化改性技术可以显著提升Pd/TiO2催化剂的H2O2选择性和产率.通过构效关系分析,可知这种改性技术可以保持Pd颗粒与TiO2间相互作用的同时,还可以促进H2O2的快速脱附,进而提升改性Pd/TiO2催化剂的H2O2直接合成效率.该改性方法简单、易控,可拓展应用到其他类型催化剂的H2O2直接合成性能调控与改进.     

Preparation of Pd/C catalysts via deposition of palladium hydroxide onto Sibunit carbon and their application to partial hydrogenation of rapeseed oil

Pd/Sibunit catalysts were prepared by deposition of palladium hydroxide onto the support surface in an alkaline medium. It was found that the palladium distribution throughout the catalyst grain, and the dispersion of Pd particles depend on (i) the order of the addition of H₂PdCl₄ and Na₂CO₃ to carbon suspension, (ii) Na₂CO₃ to H₂PdCl₄ ratio, and (iii) aging time of the mixture H₂PdCl₄ + Na₂CO₃ before its addition to the carbon. The catalysts were tested in the hydrogenation of cyclohexene and rapeseed oil under static conditions. The yield of trans-isomers as products of partial hydrogenation of rapeseed oil was found to decrease with decreasing the Pd particle size in the catalysts, as well as with increasing the Pd concentration on the periphery of the support grains.     

A new and facile synthesis of 6‐methyl‐2‐trifluoromethyl‐4‐(O,O‐ dialkyl) phosphoryl‐ quinoline

Palladium‐catalyzed coupling reaction of trifluoromethylacetimidoyl iodide with dialkyl vinylphosphonates afforded trifluoromethylated and phosphorylated α, β‐unsatured imines, which gave corresponding quinoline derivatives upon cyclization with Pd/C in nitrobenzene.     

Crossover Sorption of C2H2/CO2 and C2H6/C2H4 in Soft Porous Coordination Networks

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of “crossover sorption,” in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn₂(L1)(L2)₂]_n (PCP-1) and [Zn₂(L1)(L3)₂]_n (PCP-2) (L1= 1,4-bis(4-pyridyl)benzene, L2=5-methyl-1,3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C₂H₂/CO₂ and C₂H₆/C₂H₄, in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C₂H₂, CO₂, C₂H₆, and C₂H₄ gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host–guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host–guest and guest-guest interactions.     

Chromatographic Separation of the Enantiomers of a Series of C2-Asymmetric Bi-Naphthyl Compounds by Molecularly Imprinted Polymers

The aim of this study was to observe the chiral separation of a series of C₂-asymmetric bi-naphthyl compounds on molecularly imprinted polymers (MIPs) using 1,1′-bi-2-naphthol (BINOL) as template. MIP prepared using 4-vinylpyridine as the functional monomer showed better chiral recognition for the template than the MIPs prepared using acrylamide, 2-(diethylamino)ethylmethacrylate and 2-vinylpyridine, respectively. ¹H-NMR was used for comparison of the interactions between template and functional monomers. For chromatographic analysis the effects of mobile phase and temperature on the chiral separation were investigated. When 4-vinylpyridine was employed as the functional monomer, chiral separation of 1,1′-bi-2-naphthol and its analogues were studied. The MIP also demonstrated an ability to discriminate between enantiomers of structurally related compounds that had not been imprinted. The thermodynamic parameters of interactions between substrates and MIP in acetonitrile based mobile phase were investigated by the Van’t Hoff equation. In this study, the specific hydrogen-bonding interactions seemed to be the key factor to achieve chiral separation.