Aqueous Heck Arylation of Acrolein Derivatives: The Role of Cyclodextrin as Additive

Heck arylation of acrolein dialkyl acetal with (hetero)-aryl halides in water catalyzed by solid palladium catalysts and in presence of cyclodextrins is reported. Depending on the nature of the base, either cinnamaldehyde or 3-aryl propionic ester is obtained. It was shown that the presence of cyclodextrins in the reaction media increased the reaction rate as well as the stability of the palladium species.

     

Sulfobutyl Ether‐β‐Cyclodextrins: Promising Supramolecular Carriers for Aqueous Organometallic Catalysis

The potentialities of sulfobutyl ether‐β‐CDs derivatives as supramolecular carrier in a biphasic Tsuji–Trost reaction catalyzed by a water‐soluble palladium complex of trisulfonated triphenylphosphine have been investigated. The efficiency of these cyclodextrins (CDs) strongly depends on the average molar substitution degree of cyclodextrin and the highest rate enhancements were obtained with cyclodextrins containing about 7 sulfobutyl ether groups. This result was attributed to the absence of a strong interaction between this cyclodextrin and the trisulfonated triphenylphosphine used to dissolve the catalyst in the aqueous phase and to the presence of an extended hydrophobic cavity allowing a better molecular recognition between the substrate and the cyclodextrin. This constitutes the first example of a non‐interacting β‐cyclodextrin/phosphine couple with high catalytic activities.     

Two‐Phase Hydroformylation of Higher Olefins Using Randomly Methylated α‐Cyclodextrin as Mass Transfer Promoter: A Smart Solution for Preserving the Intrinsic Properties of the Rhodium/Trisulfonated Triphenylphosphine Catalytic System

The two‐phase hydroformylation of higher olefins with the rhodium/trisulfonated triphenylphosphine catalytic system in the presence of various chemically modified α‐cyclodextrins has been investigated. These cyclodextrins allowed us to increase greatly the reaction rate and the chemoselectivity of the reaction but, contrary to what has been observed previously with the chemically modified β‐cyclodextrins, the linear to branched aldehydes ratio was not affected by the presence of α‐cyclodextrin derivatives. Indeed, the latter was found to be similar to that obtained without any mass transfer promoter, suggesting that the catalytic species are stable in the presence of α‐cyclodextrin derivatives.     

聚苯乙烯二醋酸碘苯在芳丙酮1,2-芳基迁移重排反应中的应用

在聚苯乙烯二醋酸碘苯催化下,芳丙酮进行1,2-芳基迁移重排制得2-芳丙酸甲酯,后者水解得2-芳基丙酸。硫酸和原甲酸三甲酯的用量对合成2(6甲氧基2萘基)丙酸甲酯收率有影响,聚苯乙烯碘苯可回收利用。     

The gas-phase chemistry of cyclodextrin inclusion complexes

Complexes of cyclodextrins with amino acid analytes are produced in the gas phase and are ideal for the study of molecular recognition. In this Account, we discuss the evidence for the presence of gas-phase inclusion complexes and the nature of the interaction. The use of cyclodextrins as chiral selectors in gas-phase guest-exchange reactions is illustrated, and the nature of the enantioselectivity is discussed. The development of the enantioselective reaction into an analytical method for determining enantiomeric excess is also described.     

Thermodynamics of the encapsulation by cyclodextrins

Molecular encapsulation on a molecular basis can be performed by cyclodextrins. The inclusion of organic molecules into the interior changes the properties of these molecules, which may be used for a broad variety of applications. The affinity of guest molecules for the cavities of various cyclodextrins depends on the stereochemistry and on the interaction forces of the molecules involved. Calculations of the thermodynamic parameters show that the reaction entropy is highly important for the inclusion reaction. Completely different reaction mechanisms are observed for various types of cyclodextrins as some of these reactions show enthalpy–entropy compensation. Others are supported by the reaction entropy or are even entropically controlled. Protonation and deprotonation reactions contribute significantly to the inclusion reaction, as first of all the solubility of the compounds in water is strongly influenced by the acidity of the solution, and, moreover, all tautomeric forms of the compounds show different affinities to various cyclodextrins. Copyright © 2006 Society of Chemical Industry     

三甲基氯硅烷催化合成2-芳基苯并咪唑的研究

采用三甲基氯硅烷(TMSCl)作为路易斯催化剂催化芳醛和邻苯二胺合成了2-芳基苯并咪唑化合物.以苯甲醛和邻苯二胺的反应为模型反应,考察了催化剂与反应底物质量比、反应温度和反应溶剂对反应效果的影响,验证了三甲基氯硅烷对合成反应的催化作用.实验结果表明,三甲基氯硅烷能大大加快芳醛和邻苯二胺合成2-芳基苯并咪唑反应的进行,其...     

Convenient Ultrasound Promoted Synthesis of 2-Aryl Benzoxazoles in the Presence of KCN/Ionic Liquid as an Efficient Catalyst under Mild Conditions

A simple and efficient procedure has been developed for the synthesis of 2-aryl benzoxazoles using one-pot reaction of 2-aminophenol and aromatic or heteroaromatic aldehydes in the presence of KCN/1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) as a catalyst under ultrasound irradiation. 2-Aryl benzoxazoles were achieved in excellent yields and high purities in short reaction times. This protocol was shown to have some advantages such as readily reaction method, simplicity of the workup procedure, low cost, eco-friendly catalyst, and mild reaction conditions.     

Palladium‐Catalyzed Allylic Substitution of Allyl Vinyl Carbonate

Vinyl carbonate was found to be a very effective leaving group in palladium‐catalyzed allylic substitution. When the reaction of an equimolar amount of allyl methyl carbonate and allyl vinyl carbonate with dimethyl malonate was carried out in the presence of a palladium catalyst, allyl vinyl carbonate reacted with the nucleophile, and most of allyl methyl carbonate remained unchanged. In the reaction of a compound having allyl methyl carbonate and allyl vinyl carbonate in the molecule with tosyl amide, in the presence of a palladium catalyst, the nucleophile reacted with the allyl vinyl carbonate, and the allyl methyl carbonate remained unchanged.     

Eco-efficient Catalytic Hydrodechlorination of Carbon Tetrachloride in Aqueous Cyclodextrin Solutions

An eco-efficient process of catalytic hydrodechlorination of carbon tetrachloride into methane and chloride salts has been developed in aqueous basic medium at room temperature. The organic pollutants are trapped in water by cyclodextrins (CDs) via the formation of inclusion complexes and dechlorinated by a supported heterogeneous palladium catalyst. Catalytic investigations demonstrate that CDs act as efficient CCl₄ solubilizers and, much more interesting, as protective molecules against side reactions.     

用于偶联反应的载钯催化剂制备研究进展

偶联反应一般是指C-C偶联或C-N等的偶联,像Still反应、Suzuki反应和Buchwald反应等,它们中的反应催化剂一直以来是使用均相钯配体催化剂,对于负载型钯催化剂的使用较少。将载钯催化剂用于偶联反应是有机合成反应中均相反应多相化的典型例子,且在工业化生产中较均相催化剂更具有优势。从负载钯催化剂的制备、介孔碳的制备及反应驱动力三个方面介绍了偶联反应的近期进展,并对未来发展进行了展望。     

Mitsunobu反应合成单取代β-环糊精胺基衍生物

在超分子化学领域,胺基修饰环糊精是一类合成化学修饰环糊精的重要中间体。传统方法需要多步反应才能实现环糊精胺基衍生物的合成。以β-环糊精为起始原料,经两步Mitsunobu反应合成了标题化合物。和传统方法相比,该方法步骤短且收率较高,为环糊精衍生物的合成提供了一种新的选择。     

Synthesis of some new oxazoloquinolines and stilbyloxazoloquinolines

A new series of 2-aryl(alkyl)oxazoloquinolines (IV) were prepared by the reaction of 7-amino-8-hydroxyquinoline with aromatic (or aliphatic) aldehydes in the presence of piperidine as a catalyst. Interaction of 2-methyloxazolo[4,5-h]quinoIine with aromatic aldehydes in the presence of piperidine as a catalyst gave 2-stilbyloxazolo [4,5-h]quinolines. The structural configuration of the prepared compounds was determined by elemental and spectral analysis.     

An Amine‐, Copper‐ and Phosphine‐Free Sonogashira Coupling Reaction Catalyzed by Immobilization of Palladium in Organic–Inorganic Hybrid Materials

An immobilization of palladium in organic‐inorganic hybrid materials‐catalyzed Sonogashira coupling reaction has been described. Terminal alkynes reacted with aryl iodides and aryl bromides only in the presence of a 3‐(2‐aminoethylamino)propyl‐functionalized, silica gel‐immobilized palladium catalyst under amine‐, copper‐ and phosphine‐free reaction conditions. The reaction generates the corresponding cross‐coupling products in excellent yields. Furthermore, the silica‐supported palladium can be recovered and recycled by a simple filtration of the reaction solution and used for 30 consecutive trials without any decreases in activity.     

Hydrodechlorination of 3-chloropyridine and chlorobenzene in methanol solution over alkali-modified zirconia-supported palladium catalysts

The liquid-phase hydrodechlorination of 3-chloropyridine and chlorobenzene has been studied over alkali-modified zirconia-supported palladium catalysts. The modification of the ZrO₂ with alkali metal carbonates improves the catalytic activity of the final palladium catalyst. Therefore, the larger the ionic radii (Li⁺ < Na⁺ < K⁺), the greater the catalytic activity (TOF) of the palladium catalyst. For 3-chloropyridine, hydrodechlorination proceeds without catalyst deactivation. This is explained as the result of the interaction of reaction products (pyridine and HCl) forming pyridinium chloride, thus avoiding the detrimental effect of HCl on the palladium particles. Catalytic hydrodechlorination of chlorobenzene over Pd catalysts exhibits an initial catalytic activity (TOF) much lower than that of 3-chloropyridine and the Pd catalysts deactivate as the reaction proceeds. Finally, chlorobenzene hydrodehalogenation has also been carried out in the presence of an equimolecular amount of pyridine resulting in a decrease in the initial reaction rate on the one hand, but also in an increase in final conversion on the other.     

Synthesis of condensation polymers catalyzed by palladium-graphite

Palladium-graphite (Pd---Gr) was applied to polycondensations as a heterogeneous palladium catalyst. Catalytic activities of Pd---Gr for the Heck reaction and a carbonyl insertion reaction were investigated using the model reactions. Polycinnamamide was synthesized through the Heck reaction of N, N′-(3,4′-oxydiphenylene)bis(acrylamide) and bis(4-iodophenyl) ether catalyzed by Pd---Gr. The polymerization proceeded efficiently in the presence of tributylamine, but required a long reaction time compared with the case of homogeneous catalysts. The resulting polymer was almost white in color, which means that it was less contaminated by palladium metal. The removal and recycling of Pd---Gr were much easier than the case of homogeneous catalysts. Aramid was also synthesized through the carbonyl insertion reaction of m-diiodobenzene and bis(4-aminophenyl) ether catalyzed by Pd---Gr. The rate of carbon monoxide consumption for the polymerization catalyzed by Pd---Gr was almost equal to that catalyzed by the homogeneous palladium catalyst. In both cases, the structures of the resulting polymers were identical to those prepared by homogeneous palladium catalysts.     

The First Fluoride‐Free Hiyama Reaction of Vinylsiloxanes Promoted by Sodium Hydroxide in Water

The first cross‐coupling reaction between vinylalkoxysilanes and aryl bromides or chlorides promoted by aqueous sodium hydroxide under fluoride‐free conditions to provide styrenes is reported. The reaction is catalyzed by palladium(II) acetate or a 4‐hydroxyacetophenone oxime‐derived palladacycle either under thermal or microwave heating at 120 °C with low catalyst loading (0.01–1 mol % of palladium) in the presence of tetra‐n‐butylammonium bromide (TBAB) as additive in air. In the case of styryltriethoxysilane, the coupling with aryl or vinyl bromides takes place stereospecifically to give the corresponding stilbenes or dienes, respectively. These mild and simple reaction conditions prevent undesirable polymerization of the products.     

First Heterogeneous Ligand‐ and Salt‐Free Larock Indole Synthesis

A new ligand‐ and salt‐free procedure using heterogeneous palladium catalysts for the Larock indole and benzofuran synthesis is reported. After optimisation of the reaction conditions, good to high isolated yields have been achieved for a variety of structures. Recycling studies have shown that the palladium catalysts can be readily recovered and reused. Reactions and recovery of the palladium catalysts can be carried out in the presence of air, without any particular precaution.     

Examination of the Aromatic Amination Catalyzed by Palladium on Charcoal

The Buchwald–Hartwig amination of aryl halides with secondary amines and functionalized aromatic amines catalyzed by solid‐supported palladium is reported. The choices of ligand, base and solvent are crucial for the successful coupling. The amination of aromatic iodides, bromides and chlorides can be easily achieved with palladium on charcoal in the presence of a biphenylphosphane‐type ligand at 80–110 °C. In addition, the palladium on charcoal catalyst is easily separable after the reaction, and reusable several times with only small activity loss.     

Membrane reactor immobilized with palladium‐loaded polymer nanogel for continuous‐flow Suzuki coupling reaction

A catalytic membrane reactor, which was immobilized with palladium‐loaded nanogel particles (NPs), was developed for continuous‐flow Suzuki coupling reaction. Palladium‐loaded membranes were prepared by immobilization of NPs, adsorption of palladium ions, and reduction into palladium(0). The presence of palladium in the membrane was confirmed by the scanning electron microscopy; palladium aggregation was not observed. The catalytic activity of the membrane reactor in continuous‐flow Suzuki coupling reaction was approximately double that of a comparable reactor in which palladium ions were directly adsorbed onto an aminated membrane. This was attributed to the formation of small palladium particles. The reusability in the continuous‐flow system was higher than that in a batch system, and the palladium‐loaded membrane reactor had high long‐term stability. © 2014 American Institute of Chemical Engineers AIChE J, 61: 582–589, 2015