Ionic liquid-mediated Darzens condensation: An environmentally-friendly procedure for the room-temperature synthesis of α,β-epoxy ketones

This room-temperature Darzens condensation of α-chloroacetophenone with various aromatic aldehydes mediated by [bmim][BF₄] ionic liquid in the presence of sodium tert-butoxide resulted in the sole formation of good to excellent yields of trans-α,β-epoxy ketones in short time periods. In contrast, tert-butyl 2-chloroacetate underwent Darzens reactions with aldehydes giving mixtures of both cis and trans products with low selectivity. In all reactions, the ionic liquid was recovered and reused in the subsequent reactions without significant loss of activity.     

Asymmetric Diels-Alder reactions in ionic liquids

Recent interest in ionic liquids has developed various uses for them, including some applications by synthetic chemists. Ionic liquids have joined the potential list of non-traditional solvents for Diels-Alder reactions. We report here our own efforts to examine the rates and selectivities of carbon Diels-Alder reactions. Our investigations show that excellent diastereoselective and enantioselective carbon Diels-Alder reactions can be achieved in imidazolium ionic solvents at room temperature.     

Henry and Knoevenagel reactions catalyzed by methoxyl propylamine acetate ionic liquid

Henry reactions and Knoevenagel reactions, used to prepare substituted olefins, have been limited by complex catalyst separation. In this article, methoxyl propylamine acetate ionic liquid was used as an environmentally benign catalyst for these reactions under solvent-free condition for the first time. This ionic liquid was shown to effectively catalyze Henry reactions and Knoevenagel reaction of active nitromethane compounds with various aldehydes. Yields from the catalyzed reactions were over 99% under solvent free condition. The process is highly effective, environmentally benign, and very selective. Furthermore, methoxyl propylamine acetate ionic liquid was conveniently separated with the products and easily recycled to catalyze Knoevenagel reaction again with excellent yields. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 2, pp. 199–204. The article is published in the original.     

Aza‐Crown Ether Complex Cation Ionic Liquids: Preparation and Applications in Organic Reactions

Aza‐crown ether complex cation ionic liquids (aCECILs) were devised, fabricated, and characterized by using NMR spectroscopy, MS, thermogravimetric differential thermal analysis (TG‐DTA), elemental analysis and physical properties. These new and room‐temperature ILs were utilized as catalysts in various organic reactions, such as the cycloaddition reaction of CO₂ to epoxides, esterification of acetic acid and alcohols, the condensation reaction of aniline and propylene carbonate, and Friedel–Crafts alkylation of indole with aldehydes were investigated carefully. In these reactions, the ionic liquid exhibited cooperative catalytic activity between the anion and cation. In addition, the aza‐[18‐C‐6HK][HSO₄]₂ was the best acidic catalyst in the reactions of esterification and Friedel–Crafts alkylation under mild reaction conditions.     

Organotin perfluorooctanesulfonates as air-stable Lewis acid catalysts: synthesis, characterization, and catalysis

The reactions of 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane and dialkyltin dihalides with silver perfluorooctanesulfonate provided the corresponding sulfonates as hydrates. The number of water molecules (n) of hydration was dependent on the conditions. The distannoxane derivative was identified as n from 0.5 to 6, while in the hydrated mononuclear species and DMSO complexes n varied widely from 4 to 13. 119Sn NMR spectroscopy and conductivity measurements indicated the ionic dissociation of these compounds in solution. These compounds exhibited unusually high solubility in polar organic solvents. The ionic dissociation together with facile hydration probably causes the unusual solubility. The Lewis acidity of these compounds was found to be high among organotin derivatives on the basis of ESR spectra of superoxide/metal-ion complexes. In contrast to well-known organotin triflates, these compounds suffered no hydrolysis upon storage in open air. The high catalytic activity of the distannoxane 1 was exemplified for various carbon-carbon bond-forming reactions, such as Mukaiyama-aldol as well as -Michael reactions and allylation of aldehydes.     

Ionic liquid promoted synthesis of heterocycle-fused pyrimidine-2,4(1H,3H)-diones utilising CO2

An efficient ionic liquid system was developed for the preparation of various heterocycle-fused pyrimidine-2, 4(1H,3H)-diones in moderate to excellent yields (52–95%). It was found that [HDBN⁺][TFE^?], a simple and easily prepared ionic liquid, could act as both the solvent and reaction promoter, and that the reactions could be efficiently carried out at atmospheric pressures of CO₂.     

Ionic liquids in enzymatic catalysis and biochemical methods of analysis: Capabilities and prospects

The first Russian review systematizes and discusses the most important and promising published data on the use of ionic liquids in biocatalysis and, especially, biochemical methods of analysis. Studies on the use of ionic liquids as solvents for enzymes, new reaction media for enzymatic reactions, and components of the biosensitive layers of sensors are analyzed. The physical and chemical properties of ionic liquids used in biocatalysis are discussed. The advantages of ionic liquids over the usual solvents in homogeneous and heterogeneous reactions with the participation of enzymes from various classes are demonstrated, procedures for the coimmobilization of biocatalysts and ionic liquids with cellulose onto polymer supports and electrodes are described, and prospects for the use of enzyme-ionic liquid compositions in biochemical methods of analysis are considered.     

Ionic liquid-promoted regiospecific Friedlander annulation: novel synthesis of quinolines and fused polycyclic quinolines

Several room-temperature ionic liquids (ILs) based on 1-butylimidazolium salts with varying anions were synthesized and evaluated for the preparation of biologically active substituted quinolines and fused polycyclic quinolines using the Friedlander heteroannulation reaction. On screening, 1-butylimidazolium tetrafluoroborate [Hbim]BF4 was found to be the best ionic liquid for the heteroannulation reaction, and the reasons to this effect are well explained. The reactions proceed very well under relatively mild conditions without any added catalyst. The IL acts as a promoter for this regiospecific synthesis and can be recycled. By this green approach, various quinolines were prepared in excellent yields and purity and well-characterized.     

An evaluation of silver ionic transport in the mixed system (1−x)·CuI-x·Ag2MoO4 (0.15?x?0.6)

The origin and nature of correlation between silver ionic conduction and composition of various phases present in the case of the mixed system CuI-Ag₂MoO₄ were probed in terms of possible solid-state reactions. Detailed X-ray diffraction (XRD), differential scanning calorimetry, Fourier transform infrared, electrical transport studies involving ionic transport number data and electrical conductivity measurement were carried out in order to identify the reaction products. The feasible reaction products identified were found to determine the exact composition resulting from the completion of each solid-state reaction and hence the behavior of effective electric conduction.     

Influence of DNA on the rate of ligand substitution in platinum(II) terpyridine complexes

The kinetics of substitution of pyridine or 2-methylpyridine, by iodide or thiourea, in the complexes [Pt(4'-R'terpy)(2-Rpy)](BF4)2 (R' = o-tolyl or H; R = H or CH3) has been studied, at 25 degrees C, pH 7, and various ionic strength values, in the presence of and without calf thymus DNA. The reactions occur in one observable step, and plots of kobsd against nucleophile concentration give straight lines with zero intercepts. DNA inhibits all the reactions studied without altering the rate law; the second-order rate constants k2 decrease systematically on increasing DNA concentration and are larger at higher ionic strength values. Partitioning of the ionic reactants in solution on electrostatic grounds can account for this kinetic effect in the reaction with iodide. Iodide is kept off the double helix proximity while the dicationic complexes concentrate on it. The inhibiting effect observed for the uncharged reagent thiourea can be related to the specific binding mode of the complexes to DNA. The complexes studied are effective intercalators to double helix, and this type of interaction, which prevents attack of thiourea at platinum, decreases their actual concentration in solution. The inhibiting effect is larger for [Pt(terpy)(py)]2+ that is a better intercalator. Likewise, the decrease in the rate of substitution of 2-Rpy, at a given [DNA] on decreasing ionic strength, is due to the influence of ionic strength on the complex-DNA interactions.     

离子液体中无膦、无铜、钯催化的Sonogashira交联反应的研究

研究了离子液体中无膦、无铜、钯催化剂在Sonogashira交联反应中的催化性能. 系统考察了反应温度、溶剂、钯源、碱等因素的影响及底物的适用性. 研究结果表明, 该催化体系对各种电子效应的碘代烷和末端炔烃的Sonogashira交联反应是十分有效的, 反应在温和的条件下取得较好的收率. 此外, 该催化体系有很好的重复使用性, 循环四次后催化活性只有略微的降低.     

Ambiphilic dual activation role of a task-specific ionic liquid: 2-hydroxyethylammonium formate as a recyclable promoter and medium for the green synthesis of β-nitrostyrenes

A cost-effective task-specific ionic liquid, 2-hydroxyethylammonium formate, efficiently promotes the condensation of nitroalkanes with various aldehydes to produce β-nitrostyrenes in high to excellent yields at room temperature. This reaction does not involve any hazardous organic solvent and toxic catalyst. The ionic liquid is recovered and recycled for subsequent reactions. In addition, a novel mechanism has been proposed invoking ambiphilic dual activation influence of the ionic liquid.     

A facile preparation of tetralins from arene-1,4-diones using titanium(IV) chloride and triethylsilane

A facile method for the synthesis of tetralins has been described which uses various substituted phenylpentane-1,4-diones as starting material with a combination of TiCl₄/Et₃SiH. The synthesis involves three reactions under mild conditions. A mechanism has been proposed for the reductive cyclization through ionic hydrogenation, and titanium(IV) chloride catalyzed cyclization.     

Mukaiyama aldol reaction using ketene silyl acetals with carbonyl compounds in ionic liquids

Mukaiyama aldol reactions using ketene silyl acetals with various aldehydes proceed smoothly in ionic liquids to afford the corresponding aldol products in moderate yields.     

Enhancement of Chemical Reactions by Microwave Irradiation

Microwaves are low electromagnetic energy which induce molecular perturbation by stimulation of ionic diffusion and by enhancement of dipole rotation without causing rearrangement of molecular structures. Microwave energy irradiated on the samples in various liquid media is lost or absorbed to the samples by the following two mechanisms: ionic conduction and dipole rotation. These two effects take place simultaneously to account for the phenomenon of rapid heating associated with many practical applications of microwave irradiation. In contrast to conventional heating, the salient feat ure of “dipole rotation” constitutes one efficient form of “molecular agitation” or “molecular stirring” which can be explored for many aspects in chemical reactions. We will discuss some of the useful application of “molecular agitation” by means of microwave irradiation such as: 1. rapid hydrolysis of proteins and peptides, 2. selective hydrolysis of aspartyl peptide bond, 3. the racemization of amino acids, 4. rapid hydrolysis of sugars, 5. continuous-flow process of microwave reactions, and 6. the enhancement of coupling reactions in peptide synthesis.     

Sustainable Diels–Alder syntheses in imidazolium ionic liquids

An effective and simple protocol for the Diels–Alder reactions catalyzed and mediated by ionic liquid in conjunction with Lewis acid was studied. Diels–Alder adduct of the reaction of 1,4-benzoquinone with isoprene and 2,3-dimethyl-1,3-butadiene was obtained in good to excellent yields within the time span of 5.00–4.00 min under microwave irradiation. Due to the excellent activity of 2,3-dimethyl-1,3-butadiene as a diene, its efficiency was further analyzed by performing against four different dienophiles under various reaction conditions. The ionic liquid, 3-methyl-1-octyl-imidazolium tetrachloroaluminate mixed with Lewis acids, could be recycled and reused for consecutive cycles. The recovered ionic liquid in conjunction with Lewis acid displayed almost similar activity without any significant loss. This system is an essential upgrade and related to the reactions consuming common organic solvents at high temperatures and longer duration. Diels–Alder reactions under solventless conditions have also been investigated for the aforesaid reactions.     

An efficient one‐pot synthesis of bis‐indolylmethanes containing pyrazolyl catalyzed by Brønsted acidic ionic liquid under solvent‐free conditions

Brønsted acidic ionic liquid [PyNCH₂CO₂H][HSO₄] was found to be an effective catalyst for the condensation reactions of indoles with various 4‐formylpyrazoles to afford the corresponding bis‐indolylmethanes containing pyrazole under solvent‐free conditions. The satisfactory results were obtained with excellent yields, short reaction time, and simplicity in the experimental procedure. J. Heterocyclic Chem., (2011).     

Aza-Diels–Alder Reactions with Lanthanide Triflates: Syntheses of Quinoline and Phenanthridine Derivatives

The aza-Diels–Alder reactions of cyclopentadiene and cyclo-1,3-hexadiene with various substituted N-arylimines in the presence of Yb/Sc triflates as catalyst in MeCN at room temperature gave quinoline and phenanthridine derivatives in moderate to high yields. Some of the cycloaddition reactions were carried out in ionic liquid.     

Ionic Liquid Containing Copper(I): A New,Green, Homogeneous,and Reusable Catalyst for Click Cyclization

An ionic liquid containing copper(I) is introduced as a new, green, homogeneous, and reusable catalyst for click synthesis of 1,4-disubstituted-1H-1,2,3-triazoles from α-azido ketones and terminal alkynes in various solvents, especially in [bmim]BF₄. These cyclization reactions were efficiently performed in the presence of introduced ionic liquid catalyst with short reaction times and good yields. This catalytic ionic liquid exhibits excellent activity and can be simply recovered and reused for at least five runs without any loss in its activity.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Sonochemistry and sonoluminescence in ionic liquids, molten salts, and concentrated electrolyte solutions

Ionic liquids have favorable intrinsic properties that make them of interest as solvents for various chemical reactions. The same properties that make the liquids effective solvents also make them interesting liquids for studies involving sonochemistry, acoustic cavitation, and sonoluminescence. Recent interest in using ultrasound to accelerate chemical reactions conducted in ionic liquids necessitates an understanding of the effects of acoustic cavitation on these solvents. Here, we review our previous results on the effects of cavitation on some room-temperature ionic liquids, including the sonoluminescence spectra of molten salt eutectics and concentrated aqueous electrolyte solutions. In all cases, regardless of the essentially nonexistent vapor pressure of the solution atomic and small molecule emitters are observed in the spectra which arise from sonolysis of the ionic liquids.