A recyclable palladium-catalyzed modified Friedländer quinoline synthesis

2-Aminobenzyl alcohol reacts with an array of ketones in toluene/poly(ethylene glycol) (PEG-2000) at 100 °C in the presence of a palladium catalyst along with KOH under an atmosphere of air to give the corresponding quinolines in good yields. The catalytic system could be recovered and reused five times without any loss of catalytic activity.     

An alternative quinoline synthesis by via Friedländer reaction catalyzed by Yb(OTf)3

Quinolines have been synthesized in very good yields from 2-aminoarylketones and differently substituted carbonyl compounds in the presence of Yb(OTf)₃ as the catalyst. The method is applicable to both cyclic and acyclic carbonyl compounds with only slight differences in the experimental procedure.     

Synthesis and characterization of quinoline derivatives via the Friedländer reaction

A rapid and efficient method for the synthesis of various poly-substituted quinolines has been developed via the Friedländer condensation of 2-aminoarylaldehyde with a carbonyl compound containing a reactive α-methylene group in the presence of sodium ethoxide (10 mol %). The new tetrahydroacridine derivatives and 11H-indeno[1,2-b]quinolines were synthesized in high yield with sodium ethoxide as a catalyst via the Friedländer reaction. The conditions of reaction were discussed and the possible reaction mechanism was proposed.     

Friedländer反应中催化体系的研究进展

综述了近几年来国内外Friedländer反应中催化体系的研究进展, 其中涉及质子酸碱/Lewis酸碱催化、有机金属催化以及离子液体催化等, 并讨论了部分反应机理.     

Thorpe-Ingold effect in copper(II)-catalyzed formal hydroalkoxylation-hydroarylation reaction of alkynols with indoles

The use of Cu(OTf)₂ as a catalyst for tandem hydroalkoxylation-hydroarylation reaction of alkynes tethered with hydroxyl group is reported. The reaction proceeds at 60 °C or even at room temperature with 5 mol % catalyst loading and produces C-3-substituted indoles in good to high yields. The method was shown to be applicable to a broad range of indoles, containing electron-withdrawing and electron-donating substituents, and alkynol substrates bearing sterically demanding substituents in the tether. Interestingly, it was found that Thorpe-Ingold effect is operating for this cyclization reaction. Easy availability and low cost of Cu(OTf)₂ make this method attractive and amenable for large-scale synthesis compared to known literature methods.     

An efficient catalytic method for the Friedländer annulation mediated by peptide coupling agent propylphosphonic anhydride (T3P®)

We have demonstrated the utilization of T3P, a mild and low toxic peptide coupling agent, as a promoter and water scavenger in the Friedländer annulation, and thus introduced a highly efficient catalytic process to access carbocyclic and heterocyclic fused quinolines under microwave irradiation or a conventional heating technique. The reaction conditions are sufficiently mild to tolerate the acid and base sensitive functional groups that can serve as levers for further extension of the quinoline products.     

Photoactive amorphous molecular materials based on quinoline amines and their synthesis by Friedländer condensation reaction

A new class of conjugated quinoline amines was prepared by Friedländer condensation reaction. They showed stable amorphous state below glass transition temperatures as examined by differential scanning calorimetry and X-ray diffraction studies. Additionally, they exhibited fluorescence properties in the blue to green region of visible spectrum in both solution and solid state. Their fluorescence quantum efficiencies in chloroform were in a broad range of 3-45%. Interestingly, they formed stable fibers with micrometer thickness drawn from melt, which were characterized by polarizing optical microscopy and scanning electron microscopy studies.     

Cu(I)/Cu(II)-catalyzed allylic amination of alkenes

Allylic hydrocarbons are selectively converted to the corresponding allyl amines in good to excellent yield by reaction with aryl hydroxylamines catalyzed by a 1:1 mixture of CuCl and CuCl₂ (10 mol %). Under these conditions unsymmetrical olefins react highly regioselectively with N-functionalization at the less substituted vinylic carbon. Trapping experiments indicate that a free nitrosoarene is not an intermediate in these reactions.     

Domino synthesis of 2-arylbenzo[b]furans by copper(II)-catalyzed coupling of o-iodophenols and aryl acetylenes

A wide range of 2-arylbenzo[b]furans are synthesized through domino intermolecular C_(aryl)-C_(alkynyl) bond formation followed by intramolecular C_(alkynyl)-O bond forming cyclization via copper(II)-catalyzed coupling of o-iodophenols and aryl terminal acetylenes. This method requires neither expensive palladium catalyst nor oxophilic phosphine ligands, can tolerate different functional groups. The methodology is successfully utilized in formal synthesis of β-amyloid aggregation inhibitor 5-chloro-3-[4-(3-diethylaminopropoxy)benzoyl]-2-(4-methoxyphenyl) benzofuran.     

Homogeneous catalysis,heterogeneous recycling: a new family of branched molecules with hydrocarbon or fluorocarbon chains for the Friedländer synthesis of quinoline under solvent-free conditions

A new family of branched catalysts with hydrocarbon or fluorocarbon chains was used to catalyze Friedländer reaction between 2-aminoarylketones and α-methylene ketones under solvent-free conditions in good to excellent yields. The catalysts exhibit temperature-dependent solubility and such a thermomorphic character allows them to be recovered by filtration conveniently at room temperature and reused at least five times. To some extent, the branched catalysts with hydrocarbon chains are superior to those with fluorocarbon chains, as they are cheaper and more biodegradable.     

Hydroxyapatite-supported copper(II)-catalyzed azide-alkyne [3+2] cycloaddition with neither reducing agents nor bases in water

Copper(II)-exchanged hydroxyapatite, prepared by ion-exchanging of Ca(II) in calcium hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] with Cu(NO₃)₂ at 70 °C in water, functions as a reusable heterogeneous catalyst with neither reducing agents nor bases for azide-alkyne [3+2] cycloaddition at 50 °C in water under air.     

An efficient copper(II)-catalyzed synthesis of benzothiazoles through intramolecular coupling-cyclization of N-(2-chlorophenyl)benzothioamides

A wide range of 2-aryl or 2-alkyl-substituted benzothiazoles are synthesized through intramolecular C_(aryl)-S bond forming-cyclization using copper(II)-BINAM-catalyzed coupling of less reactive N-(2-chlorophenyl)benzo or alkylthioamide under mild reaction conditions (82 °C).     

Highly controlling selectivity of copper(I)-catalyzed azide/alkyne cycloaddition (CuAAC) between sulfonyl azids and normal alkynes or propynoates

In this article, a combination of Cu(OAc)₂·H₂O/2-aminophenol was developed as a highly efficient and controlling catalytic system for sulfonyl azids involved CuAAC. By using this catalytic system, sulfonyl azids reacted with normal alkynes or propynoates to selectively give the ring products or the chain products, respectively, in excellent yields within minutes. HOAc in situ produced in the reaction has been proved to be a super protonation reagent, by which the unstable intermediate 5-cuprated 1,2,3-triazole was protonated efficiently to yield ring-product 1-sulfonyl 1,2,3-trizoles. The control experiments also proved that 2-aminophenol played dual roles as both ligand and reductant, which led to the cheap and chemically stable Cu(OAc)₂·H₂O being an efficient copper source for our purpose.     

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for acetal formation

Commercially available copper(II) tetrafluoroborate hydrate has been found to be a highly efficient catalyst for dimethyl/diethyl acetal formation in high yields from aldehydes and ketones by reaction with trimethyl/triethyl orthoformate at room temperature and in short period. Acetalisation was carried out under solvent-free conditions with electrophilic aldehydes/ketones. For weakly electrophilic aldehydes/ketones (e.g., benzaldehyde, cinnamaldehyde and acetophenone) and for aldehydes having a substituent that can coordinate with the catalyst, the corresponding alcohol was used as solvent.     

Multifunctional catalysis of a ruthenium-grafted hydrotalcite: one-pot synthesis of quinolines from 2-aminobenzyl alcohol and various carbonyl compounds via aerobic oxidation and aldol reaction

The Ru-grafted hydrotalcite was found to be an excellent multifunctional catalyst for one-pot synthesis of quinolines from 2-aminobenzyl alcohol and various carbonyl compounds. These quinolines were obtained through aerobic oxidation by the Ru species, followed by aldol reaction on base sites of the hydrotalcite.     

Efficient synthesis of 2-(2′-hydroxyphenyl)benzoxazole by palladium(II)-catalyzed oxidative cyclization

An efficient method for the synthesis of 2-(2′-hydroxyphenyl)benzoxazole has been developed by using palladium-mediated oxidative cyclization.     

Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace copper(II) determination

This paper described a facile and direct electrochemical method for the determination of ultra-trace Cu²⁺ by employing amino-functionalized mesoporous silica (NH₂-MCM-41) as enhanced sensing platform. NH₂-MCM-41 was prepared by using a post-grafting process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fourier transform infrared (FTIR) spectroscopy. NH₂-MCM-41 modified glassy carbon (GC) electrode showed higher sensitivity for anodic stripping voltammetric (ASV) detection of Cu²⁺ than that of MCM-41 modified one. The high sensitivity was attributed to synergistic effect between MCM-41 and amino-group, in which the high surface area and special mesoporous morphology of MCM-41 can cause strong physical absorption, and amino-groups are able to chelate copper ions. Some important parameters influencing the sensor response were optimized. Under optimum experimental conditions the sensor linearly responded to Cu²⁺ concentration in the range from 5 to 1000 ng L⁻¹ with a detection limit of 0.9 ng L⁻¹ (S/N = 3). Moreover, the sensor possessed good stability and electrode renewability. In the end, the proposed sensor was applied for determining Cu²⁺ in real samples and the accuracy of the results were comparable to those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) method.     

Phosphorus(V)-catalyzed deoxydichlorination reactions of aldehydes

A phosphine oxide-catalyzed conversion of aldehydes into 1,1-dichlorides is reported. The reaction proceeds via a phosphorus(V)-catalysis manifold in which phosphine oxide turnover is achieved using oxalyl chloride as a consumable reagent. The new method is applicable to a range of aldehydes and, in combination with palladium-catalyzed reductive dimerization, gives rise to a new catalytic approach to the synthesis of stilbenes and a short formal synthesis of resveratrol.     

Chitosan-SO3H: an efficient,biodegradable, and recyclable solid acid for the synthesis of quinoline derivatives via Friedländer annulation

Chitosan-SO₃H is found to catalyze the Friedländer condensation/annulation reaction of 2-aminoaryl ketones with α-methyleneketones to produce the corresponding quinoline derivatives in high yields in short reaction times. The use of recyclable and biodegradable chitosan-SO₃H makes this method quite simple, more convenient, and economically viable compared to acid catalyzed methods reported in the literature.     

Chiral binuclear copper(II) catalyzed nitroaldol reaction: scope and mechanism

Chiral binuclear copper(II) Schiff base complexes 4a-g have been prepared from aldehydes 1a,b, (S)-amino alcohols 2a-f, and Cu(OAc)₂·1H₂O in high yield. Their catalysis is studied for the addition of nitroalkanes to aldehydes at ambient conditions with 76:24 er.