Functionalized Imidazolium Salts Research Articles

Chan−Evans−Lam coupling for the synthesis of N–aryl derivatives catalyzed by copper(I) chloride and sterically varied imidazolium salts at mild reaction conditions

First-row transition–metal–catalyzed organic transformations have received colossal interest in the modern synthetic organic chemistry due to their step– and atom–economic approaches. As a consequence, direct arylation of azoles through C–H or N–H activations acquired a broad spectrum of applications for accessing valuable small organic molecules that are of pharmaceutical interest. In this connection, sterically varied coumarin–functionalized imidazolium salts bearing bromide (5–7) and hexafluorophosphate anions (8–10) have been prepared and used as NHC precursors. The salts have been characterized by both, spectroscopic and analytical techniques. A hexafluorophosphate salt 9 was also studied for its structure using the single-crystal XRD technique. The salts that indeed, generate carbene that trap Cu(I) to form Cu(I)–NHC complexes in situ for the Chan−Evans−Lam C–N coupling of 1H–azoles/anilines and phenyl/thiopheneboronic acids, resulting in the formation of N–aryl derivatives in moderate to excellent yields. The structure-activity relationship studies revealed that the steric bulk around the metal center would help increase the catalytic Chan−Evans−Lam C–N coupling potential of the catalysts.

Selective Oxidation of Glycerol via Acceptorless Dehydrogenation Driven by Ir(I)-NHC Catalysts.

Iridium(I) compounds featuring bridge-functionalized bis-NHC ligands (NHC = N-heterocyclic carbene), [Ir(cod)(bis-NHC)] and [Ir(CO)2(bis-NHC)], have been prepared from the appropriate carboxylate- or hydroxy-functionalized bis-imidazolium salts. The related complexes [Ir(cod)(NHC)2]+ and [IrCl(cod)(NHC)(cod)] have been synthesized from a 3-hydroxypropyl functionalized imidazolium salt. These complexes have been shown to be robust catalysts in the oxidative dehydrogenation of glycerol to lactate (LA) with dihydrogen release. High activity and selectivity to LA were achieved in an open system under low catalyst loadings using KOH as a base. The hydroxy-functionalized bis-NHC catalysts are much more active than both the carboxylate-functionalized ones and the unbridged bis-NHC iridium(I) catalyst with hydroxyalkyl-functionalized NHC ligands. In general, carbonyl complexes are more active than the related 1,5-cyclooctadiene ones. The catalyst [Ir(CO)2{(MeImCH2)2CHOH}]Br exhibits the highest productivity affording TONs to LA up to 15,000 at very low catalyst loadings.

Iron‐Based Imidazolium Salt as Dual Lewis Acid and Redox Catalyst for the Aerobic Synthesis of Quinazolines

AbstractA low transition temperature mixture formed with 1‐butyl‐3‐(methoxycarbonylmethyl)imidazolium chloride and iron(III) chloride has proven to be an efficient catalyst for the synthesis of quinazolines following a sequence of condensation‐cyclization‐oxidation reactions. The protocol is simple and effective for coupling 2‐acylanilines and benzylamines to form nitrogen containing heterocycles with moderate to excellent yields (up to 93 %), being possible to perform the reaction in preparative scale. The functionalized imidazolium salt is crucial for the activation of the reagents under solvent‐free conditions, and the presence of iron in the catalyst mediates the oxidation step with atmospheric oxygen. These features make the presented procedure better, from an environmental point of view, than other processes previously described. For this comparison, different “green” metrics have been used, such as atom economy, stoichiometric factor, reaction mass efficiency, E‐factor, and EcoScale.

Functionalized imidazolium salt: an efficient catalyst for Buchwald–Hartwig type C–N cross-coupling of (hetero)aryl chlorides/bromides with amines under solvent-, inert gas-, and base-free ambience

The intermingling of novel imidazolium salt (HL1-Br) and Cu(OAc)2 has been marked down as a highly efficient catalytic system for Buchwald–Hartwig-type C–N coupling of a variety of amines with (hetero) aryl bromides/chlorides.

Highly Efficient Reusable Carboxy Group Functionalized Imidazolium Salts for a Simple and Cost-effective Preparation of pyrano[2,3-d]pyrimidinone Derivatives

In the current study, environmentally benign and cost-effective procedures were suggested for the preparation of carboxy group functionalized imidazolium salts, including [Cmmim]BF4 - or [Cmmim]Br- as a new, reusable Brønsted acidic ionic liquid (BAIL) catalyst. Then, the catalytic performance of [Cmmim]BF4 - or [Cmmim]Br- were successfully inspected towards the three---components one---pot preparation of pyrano[2,3-d]pyrimidinone derivatives 4a-4q. The mentioned procedures show short reaction times, easy work-up procedure, green conditions, high yields of the products, high potent of recovering, and reusing capability. The current study is useful and adequate for the application and development of imidazolium salts on the basis of green chemistry principles. An aromatic aldehyde (1 mmol), barbituric acid (1 mmol), and malononitrile (1 mmol) were placed in a round---bottomed flask containing ethanol (5 mL). BAILs A and B (0.1 mmol, 10 mol%) were added to the mixture. The suspension was magnetically stirred at room temperature for an appropriate time (Table 2). After completion of the reaction, which was monitored by TLC (n---hexane:ethyl acetate = 3:1), the pure product was filtered off to separate the catalyst, washed with water, and recrystallized from ethanol to afford the pure compound. After separation of the product, the catalyst was recovered by evaporation of water, washed with Et2O, dried under vacuum for 2 h, and reused for the same reaction. The mentioned procedure shows short reaction times, easy work-up procedure, green conditions, high yields of the products, and high potent of recovering and reusing capability. In this study, we unveiled the synthesis of a new acetic acid functionalized ionic liquids [Cmmim]BF4 - BAIL A or [Cmmim]Br- BAIL B and their application for the preparation of pyrano[2,3-d]pyrimidinone derivatives via a three-component reaction among various aromatic aldehydes, barbituric acid, and malononitrile under mild and metal-free conditions. A wide range of pyrano[2,3-d]pyrimidinone derivatives bearing diverse functional groups was obtained in short reaction and excellent yields. Operational simplicity, recoverability, and reusability of catalysts, cheap and chemically stable reagents, high catalytic activity, easy work-up, and the eco-friendly procedure, make this method environmentally benign and cost-effective.

Efficient Thiophene Synthesis Mediated by 1,3‐Bis(carboxymethyl)imidazolium Chloride: C‐C and C‐S Bond Formation

Thiophene derivatives have been prepared by means of a functionalized imidazolium salt [1,3‐bis(carboxymethyl)imidazolium chloride] acting as a catalyst. The heterogeneous catalyst has allowed to carry out the reactions with no solvent or inert atmosphere. Different aryl methyl ketones have reacted with elemental sulfur to selective produce 2,4‐substituted thiophenes. Furthermore, the reaction of sulfur with cyclic ketones has enabled the preparation of polycyclic compounds. This protocol is simple and effective for preparing thiophene derivatives, even in a preparative scale. The thiophene synthesis described presents remarkable sustainability with an E‐factor of 7.4, the solvent‐free conditions being crucial for this feature. The catalyst is straightforwardly prepared, and it is easily separated from the reaction mixture, making its reuse possible.

Imidazolium Salts of Ruthenium Anionic Cyclopentadienone Complexes: Ion Pair for Bifunctional Catalysis in Ionic Liquids

The reactivity of the dinuclear complex dicarbonyl[η4‐3,4‐bis(4‐methoxyphenyl)‐2,5‐diphenylcyclopenta‐2,4‐dienone] (2) with imidazolium salts has been studied using a library of variously functionalized imidazolium salts, and leading to a class of ruthenium anionic complexes of the type [dicarbonyl{η4‐3,4‐bis(4‐methoxyphenyl)‐2,5‐diphenylcyclopenta‐2,4‐dienone} (halide)Ru][1,3‐disubsittuted‐imidazolium] (4) in the form of ion pair with imidazolium. The reaction is clean, general and quantitative and the complexes formed are stable to air and moisture both in the solid state and in solution. The ionic complexes 4 show affinity for ionic liquids and represent stable precursors of a catalytic active species, likely similar to those generated from Shvo catalyst, a well‐established homogeneous bifunctional catalyst for hydrogen transfer. Our approach allows the use of green ionic liquids (IL) as solvents, providing better control of catalytic reactions involving 4, and easier catalyst recycle. IL‐supported ionic pair catalysts exhibit interesting catalytic activity (up to > 99 % of conversion) in the transfer hydrogenation of a model compound such as 4‐fluoroacetophenone. The IL‐supported redox catalysts can be also recycled exploiting the biphasic nature of the system. The synthetic method here discussed represents a novelty within the field of IL‐supportation and is potentially useful for the heterogenization of the catalysts.

Effective and Sustainable Access to Quinolines and Acridines: A Heterogeneous Imidazolium Salt Mediates C–C and C–N Bond Formation

Quinoline and acridine derivatives have been prepared using a functionalized imidazolium salt as heterogeneous catalyst. Different ketones have been coupled with 2‐aminobenzaldehydes and 2‐aminoaryl ketones under solvent‐free conditions, employing 1,3‐bis(carboxymethyl)‐imidazolium chloride as a catalyst. The protocol is simple and effective for the synthesis of a variety of nitrogen containing heterocycles (> 35 examples) with moderate to excellent yields (up to 96 %), being possible to perform the reaction in preparative scale. Additionally, 3‐acetylquinolines have been transformed, under solvent‐free conditions, into quinolyl chalcone derivatives by means of the same catalyst. Thus, the catalytic system mediates both reactions effectively in a tandem procedure. Furthermore, the catalyst is easily separated from the reaction mixture and can be reused without loss of activity (up to 8 cycles) which remarks its sturdiness. The E‐factors are in the range of 14–23, both for the formation of quinolines and for the tandem reaction, which demonstrates the sustainability of the protocols described.

Synthesis of Functionalized Imidazolium Salts via Iodine-Mediated Annulations of Enamines.

A novel annulation reaction of two enamine molecules with iodine under basic conditions to form 4-functionalized imidazolium salts has been established. In this reaction, iodine acts as both an iodinating reagent and a Lewis acid catalyst. Features of this synthetic method include facilitative preparation of substrates, no use of transition metals, mild reaction conditions, simplicity of operation, and gram scale synthesis.

Nickel(II)- and Palladium(II)-NHC Complexes from Hydroxypyridine Functionalized C,O Chelate Type Ligands: Synthesis, Structure, and Catalytic Activity toward Kumada–Tamao–Corriu Reaction

Hydroxypyridine functionalized imidazolium salts (2a–c) have been prepared in a one pot neat reaction between alkyl/aryl imidazoles and 2-chloro-3-hydroxypyridine. The imidazolium salts were used a...

Chemodivergent, multicomponent-tandem facile synthesis of novel 1H-pyrazolo[1,2-b]phthalazine-5,10-dione using acetic acid functionalized imidazolium salt {[cmdmim]I} as a recyclable catalyst

A novel one-pot four-component, highly efficient and environmentally benign approach for the synthesis of a wide range of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives in the presence of acetic acid functionalized imidazolium salt as a newly synthesized Brønsted acid catalyst is described.

Phosphine Functionalized NHC Ligands and Their Cyclopentadienide Nickel(II) Complexes

By reaction of phosphine functionalized imidazolium salts with nickelocene, a series of cationic 18 VE nickel(II) half‐sandwich complexes were obtained in high yields. Herein the central nickel(II) atoms are coordinated in a chelating fashion by the N‐heterocyclic carbene (NHC) and the phosphine donor sites. The so obtained chelating ring can be opened by cyanide leading to neutral cyanidonickel(II) NHC complexes. Application of imidazolium salts functionalized with thiophosphine groups prevents the formation of chelate complexes. Instead neutral chloridonickel(II) NHC species are obtained.

Comparative Study of Catalytic Systems Formed by Palladium and Acyl‐Substituted Imidazolium Salts

AbstractAmino amides, which are readily accessible from amino acids, were used in the preparation of both monoamido and diamido functionalized imidazolium salts in very straightforward protocols. Different catalytic systems formed with palladium(II) acetate and acyl functionalized imidazolium salts were tested in the Matsuda‐Heck reaction. The comparative study revealed that the presence of one carbamoyl moiety in the N‐heterocyclic carbene precursor is more beneficial during the catalytic process. Thus, better activity was observed with the catalytic system formed using 3‐benzyl‐1‐(N‐phenylcarbamoylmethyl)imidazolium chloride in a 1:1 metal/ligand ratio. Moreover, this fact was evidenced by means of UV/vis studies.

Preparation, characterization, and first catalytic application of a novel phosphotungstic acid-containing ionic liquid immobilized on CuFe2O4@SiO2 magnetic nanoparticles in the synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones

A novel heterogeneous acidic ionic liquid based on functionalized imidazolium salt of phosphotungstic acid (H3PW12O40, denoted as PW), immobilized on CuFe2O4@SiO2 magnetic nanoparticles, denoted as CuFe2O4@SiO2@C3-Imid-C4SO3-PW, was prepared and characterized using FT-IR, SEM, EDX, and VSM techniques. High activity of the prepared material as a novel catalyst was evaluated in one-pot synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones by reaction of phthalhydrazide with an aromatic aldehyde and malononitrile under solvent-free conditions. The process gave high yields of the products over short reaction time. The catalyst was efficiently recovered by magnetic decantation and used repeatedly without significant loss of its activity.

Microwave-Assisted Rapid Synthesis of Pyrido[2, 3-d :6,5-d ]dipyrimidine-2,4,6,8-tetraones over Sulfonic Acid Functionalized Imidazolium Salts under Solvent-Free Condition

Seven numbers of sulfonic acid functionalized imidazolium salts (ionic liquids) have been tested for the synthesis of pyrido[2, 3-d:6,5-d]dipyrimidine-2,4,6,8-tetrone derivative with completely aromatic pyridine ring. [Dsim]Cl is found to be the best among them to carry out the synthesis via condensation of 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione with aromatic aldehydes within minutes under microwave irradiation, paving the way for an excellent methodology towards the synthesis of a series of pyrido[2, 3-d:6,5-d]dipyrimidine-2,4,6,8-tetrone. The catalyst can easily be recovered and reproduced, and the reproduced catalyst is found to be equally effective as the fresh one for the purpose. The methodology is quite simple, fast and general. In comparison to already described methodologies, it enjoys additional advantage of being carried out under solvent-free condition. The synthesized compounds are found to possess remarkable activity against S. aureus and K. pneumonia among the tested bacterial strains.

Acetic acid functionalized ionic liquid systems: An efficient and recyclable catalyst for the regioselective ring opening of epoxides with NaN3

In the present study, an environmentally benign, efficient, and solvent-free procedure was developed for the synthesis of 1,2-azidoalcohols by the regioselective ring opening of some epoxides with sodium azide (NaN3) in the presence of an acetic acid functionalized imidazolium salt [Cmmim]BF4 or [Cmmim]Br as a green and Brønsted acidic ionic liquid (BAIL) catalyst under mild and neutral reaction conditions at 60 °C. The remarkable features of this procedure are excellent regioselectivity, simple work-up procedure, high yields of products, short reaction times, and ease of recyclability of ionic liquids.

ChemInform Abstract: Highly Efficient Catalysis of Retro‐Claisen Reactions: From a Quinone Derivative to Functionalized Imidazolium Salts.

AbstractImidazolium‐4‐carboxylate salts are prepared for the first time via a retro‐Claisen reaction of quinone‐fused imidazolium salts.

Highly Efficient Catalysis of Retro-Claisen Reactions: From a Quinone Derivative to Functionalized Imidazolium Salts.

A new and efficient method for the preparation of several imidazolium salts containing an ester group in the C4 position of the aromatic ring through a retro-Claisen reaction pathway between a quinone derivative and several alcohols is described. This new organic transformation proceeds in the absence of a catalyst, but it is greatly catalyzed by different Lewis acids, especially with AgOAc at a very low catalyst loading and in very short reaction times. The process takes place by the nucleophilic attack of the carbonyl groups by the alcohol functionality, thus promoting a double C-C bond cleavage and C-H and C-O bond formation. This reaction represents the first example of this type between a quinone derivative and alcohols.

ChemInform Abstract: Tandem Knoevenagel—Michael‐Cyclocondensation Reactions of Malononitrile, Various Aldehydes and Dimedone Using Acetic Acid Functionalized Ionic Liquid.

An efficient solvent-free protocol for the synthesis of tetrahydrobenzo[b]pyrans by the condensation of malononitrile, dimedone and various aldehydes in the presence of acetic acid functionalized imidazolium salts (1-carboxymethyl-3-methylimidazolium bromide {[cmmim]Br} and 1-carboxymethy1-3-methylimidazolium tetrafluoroborate {[cmmim][BF4]}) as reusable catalysts has been reported. The turn over frequency (TOF) values of the catalysts are higher than some of the previously reported catalysts. Also, thermal gravimetric analysis (TGA), differential thermal gravimetry (DTG), X-ray diffraction analysis (XRD) and calculations of the size and inter-planer distance of the catalysts have been reported in this work.

Condensation of 2-naphtol with arylaldehydes using acetic acid functionalized ionic liquids as highly efficient and reusable catalysts

An efficient solvent-free protocol for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes from the condensation of 2-naphthol with arylaldehydes, using acetic acid functionalized imidazolium salts (1-carboxymethyl-3-methylimidazolium bromide ([cmmim]Br) and 1-carboxymethy1-3-methylimidazolium tetrafluoroborate ([cmmim]BF 4 ) as reusable catalysts, has been developed. The turn over frequency on the catalysts is several times higher than the other previously reported catalysts. Also, thermal gravimetric analysis and powder X-ray diffraction pattern of the catalysts have been studied. The catalytic activity of acetic acid functionalized imidazolium salts as reusable catalysts were investigated for the synthesis of 14-aryl-14H- dibenzo[a,j]xanthenes. Thermal gravimetric analysis and powder X-ray diffraction patterns of the catalysts have been studied in this investigation.