Molecular iodine: a highly efficient catalyst in the synthesis of quinolinesvia Friedländer annulation

Visible-light-driven radical Friedländer hetero-annulation of 2-aminoaryl ketone and α-methylene carbonyl compound via organic dye fluorescein through a single-electron transfer (SET) pathway

The discoveries recommend that the photoinduced conditions of fluorescein-determined go about as impetus for photochemically combining polysubstituted quinolines in ethanol at room temperature under air environment by means of revolutionary Friedländer hetero-annulation of 2-aminoaryl ketone and α-methylene carbonyl compound. This study lays out an original capability for photochemically orchestrating fluorescein. This non-metallic organic dye is economically accessible and modest, producing great outcomes, accelerating the cycle, and achieving a high compound economy. The turnover number (TON) and turnover recurrence (TOF) of polysubstituted quinolines have been determined. This cycle will likewise run on a gram scale, demonstrating the chance of modern applications.

Friedlӓnder's synthesis of quinolines as a pivotal step in the development of bioactive heterocyclic derivatives in the current era of medicinal chemistry

In the current scenario of medicinal chemistry, quinoline plays a pivotal role in the design of new heterocyclic compounds with several pharmacological properties, so the search for new synthetic methodologies and their application in drug discovery has been widely studied. So far, many procedures have been performed for the preparation of quinoline scaffolds, among which Friedländer quinoline synthesis plays an important role in obtaining these heterocycles. The Friedländer reaction involves condensation between 2-aminobenzaldehydes and keto-compounds. The quinoline nucleus, once obtained through the Friedländer synthesis, has been extensively modified so that these derivatives can exhibit a large number of biological activities such as anticancer, antimalarial, antimicrobial, antifungal, antituberculosis, and antileishmanial properties. In this work, the focus is on the applicability of the Friedländer reaction in the synthesis of various types of bioactive heterocyclic quinoline compounds, which to date has not been reported in the context of medicinal chemistry. The main part of this review selectively focuses on research from 2010 to date and will present highlights of the Friedländer quinoline synthesis procedures and findings to address biological and pharmacological activities.

The development of Friedländer heteroannulation through a single electron transfer and energy transfer pathway using methylene blue (MB+)

The radical Friedländer hetero-annulation of 2-aminoaryl ketone and -methylene carbonyl compound was used to develop a green tandem approach for the metal-free synthesis of polysubstitutedquinolines. At room temperature in an ethanol solvent, photo-excited state functions generated from MB+ were used as single-electron transfer (SET) and energy transfer (EnT) catalysts, utilizing visible light as a renewable energy source in the air atmosphere. The purpose of this research is to increase the use of a nonmetal cationic dye that is both inexpensive and widely available. High yields, energy-effectiveness, high atom economy, time-saving features of the reaction, and operational simplicity, and the least amount of a catalyst are the benefits of this study. As a result, a wide range of ecological and long-term chemical properties are obtained. Polysubstitutedquinolines' turnover number (TON) and turnover frequency (TOF) have been calculated. Surprisingly, such cyclization can be accomplished on a gram scale, indicating that the process has industrial potential.

Synthesis of 1,8-Naphthyridines by the Ionic Liquid-Catalyzed Friedlander Reaction and Application in Corrosion Inhibition

A several of basic ionic liquids (ILs) were synthesized as green solvents and catalysts for the preparation of 1,8-naphthyridyl derivatives via the Friedlander reaction. [Bmmim][Im] exhibited remarkable catalytic activity to achieve the synthetic targets, and the reaction conditions were optimized. The model product 2,3-diphenyl-1,8-naphthyridine (1,8-Nap), with carboxyethylthiosuccinic acid (CETSA) to form an IL corrosion inhibitor ([1,8-Nap][CETSA]), and its corrosion inhibition performance for Q235 steel in 1 M HCl were researched by weight loss measurements, and the results showed that the inhibition efficiency was 96.95% when the concentration of [1,8-Nap][CETSA] was 1 mM at 35 °C. The electrochemical test verified that [1,8-Nap][CETSA] acted as a mixed-type inhibitor but mainly exhibited cathodic behavior. The inhibitor adsorbed on the metal surface was further proved by surface topography analysis.

Metal-free synthesis of quinoline-2,4-dicarboxylate derivatives using aryl amines and acetylenedicarboxylates through a pseudo three-component reaction

An efficient, useful and one-pot protocol for the synthesis of quinoline-2,4-dicarboxylate scaffolds is accomplished from aryl amines and dimethyl/diethyl acetylenedicarboxylates using 20 mol% molecular iodine as a catalyst in acetonitrile at 80 °C. In addition, the mechanistic explanation for the formation of the desired products is disclosed. The pivotal role of molecular iodine in the formation of the major products, diester quinoline derivatives, and the minor product, triesters, in two cases is described in the mechanism. The notable advantages of this method are non-involvement of a metal catalyst, avoiding of metal contamination in the final product as well as waste generation, use of a low cost and eco-friendly catalyst, ease of handling, high regioselectivity, shorter reaction time, the formation of one C-N and two C-C bonds and a broad substrate scope with good yields.

Imidazoles and Oxazoles from Lapachones and Phenanthrene-9,10-dione: A Journey through their Synthesis, Biological Studies, and Optical Applications

Diverse structural frameworks are found in natural compounds and are well known for their chemical and biological properties; such compounds include the imidazoles and oxazoles. Researchers worldwide are continually working on the development of methods for synthesizing new molecules bearing these basic moiety and evaluating their properties and applications. To expand the knowledge related to azoles, this review summarizes important examples of imidazole and oxazole derivatives from 1,2-dicarbonyl compounds, such as lapachones and phenanthrene-9,10-diones, not only regarding their synthesis and biological applications but also their photophysical properties and uses. The data concerning the latter are particularly scarce in the literature, which leads to underestimation of the potential applications that can be envisaged for these compounds.

Iodine-catalyzed efficient synthesis of xanthene/thioxanthene-indole derivatives under mild conditions

An iodine-catalyzed nucleophilic substitution reaction of xanthen-9-ol and thioxanthen-9-ol with indoles has been developed, providing an efficient procedure for the synthesis of xanthene/thioxanthene-indole derivatives with good to excellent yields. This protocol offers several advantages, such as short reaction times, green solvent, operational simplicity, easily available catalyst and mild reaction conditions. Moreover, this method showed good tolerance of functional groups and a wide range of substrates.

Application of 2,4-bis(halomethyl)quinoline: synthesis and biological activities of 2,4-bis(benzofuran-2-yl)- and 2,4-bis(aroxymethyl)quinolines

In the present investigation, the synthesis of a new type of halomethylquinoline building block, i.e., ethyl 4-(bromomethyl)-2-(chloromethyl)quinoline-3-carboxylate, and its synthetic applications in the reaction with salicylaldehydes or phenols to make a range of structurally novel and intriguing 2,4-bis(benzofuran-2-yl)quinoline- and 2,4-bis(aroxymethyl)quinoline-3-carboxylic acids is described. Our newly synthesized compounds belong to a new class of quinoline derivatives, and their structures were elucidated on the basis of their spectral data and elemental analyses. Screening for in vitro anti-tubercular against Mycobacterium smegmatis and anti-bacterial activities against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa was carried out. Compounds 5e and 5g showed significant anti-tubercular activity comparable with the reference rifampicin and might be used as promising candidates for further investigation.

An Efficient and Green Microwave-Assisted Synthesis of Quinoline DerivativesviaKnoevengal Condensation

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We have developed an efficient and green synthesis of quinoline derivatives using L-proline under Knoevenagel condensation. L-proline was found to be an efficient catalyst for the Knoevenagel condensation of substituted 2-aminoaryl ketones 1 with the active methylene compounds 2, affording quinolone derivatives 3. The reaction has been done under conventional as well as under microwave conditions. The latter procedure has been found to be much more efficient in terms of time and yield.

Synthesis of (E)-2-amino-N'-benzylidenehexahydroquinoline-3-carbohydrazide

A one-pot, multi-component protocol for the synthesis of a new class of functionalized quinoline carbohydrazide derivatives via reaction of various anilines, dimedone, aromatic aldehydes, and cyanoacetohydrazide is described. The reactions are completed in the presence of catalytic amount of piperidine, respectively, in melt conditions and then in ethanol/water (1:1) as green solvent at 80 °C. Mild conditions, green medium, short reaction times, simple workup and purification process with no chromatographic technique, and good yields are the main advantages of this method.

Synthesis of hexahydro-4-phenylquinoline-3-carbonitriles using Fe3O4@SiO2-SO3H nanoparticles as a superior and retrievable heterogeneous catalyst under ultrasonic irradiations

An efficient synthesis of hexahydro-4-phenylquinoline-3-carbonitriles is described by the four-component condensation reaction of cyclohexanone, ammonium acetate, malononitrile, and aromatic aldehydes using Fe3O4@SiO2-SO3H nanoparticles as a superior and retrievable heterogeneous catalyst under ultrasonic irradiations. The reusability of the catalyst and little catalyst loading, excellent yields, short reaction times, using the sonochemical procedure as a green process and an alternative energy source are some benefits of this method.

Indium(III) Triflate-Catalyzed Reactions of Aza-Michael Adducts of Chalcones with Aromatic Amines: Retro-Michael Addition versus Quinoline Formation

The indium(III) triflate-catalyzed reaction of aza-Michael adducts of chalcones with aromatic amines has been investigated. The Michael adducts derived from substituted anilines and chalcones underwent retro-Michael addition to give the original starting materials, whereas the adducts derived from 1-naphthylamines and chalcones afforded quinolines. A six-membered cyclic transition state has been proposed to explain the retro-Michael addition, while a Povarov mechanism has been put forward to explain the quinoline formation.

Facile Construction of Quinoline-2-carboxylate Esters through Aerobic Oxidation of Alkyl 4-Anilinocrotonates Induced by a Radical Cation Salt

A facile construction of quinoline-2-carboxylate esters through an aerobic oxidation of alkyl 4-anilinocrotonates is described. In the presence of dioxygen, sp³ C-H bonds in 4-anilinocrotonates can easily be oxidized by using a catalytic amount of a radical cation salt, providing a radical intermediate. After further oxidation and domino cyclization, the desired quinoline derivatives were afforded in high yields. This reaction provides a new way to construct the pharmaceutically relevant quinoline skeleton, avoiding harsh reaction conditions and tedious starting material synthesis.

A NbO type Cu(ii) metal-organic framework showing efficient catalytic activity in the Friedländer and Henry reactions

A three-dimensional NbO type porous metal-organic framework 1 containing both tertiary amine groups and paddle wheel dinuclear Cu₂(COO)₄ secondary building units as the active centre was synthesized at room temperature. The activated framework 1' can be used as an efficient heterogeneous catalyst for the synthesis of quinoline derivatives by the Friedländer reaction and for the synthesis of β-nitroalcohols by the Henry (nitroaldol) reaction. This MOF-based heterogeneous catalyst is easily recycled and reused further without losing its structural integrity and catalytic activity.

Dual Behavior of Iodine Species in Condensation of Anilines and Vinyl Ethers Affording 2-Methylquinolines

A metal-free, mild and efficient method for the synthesis of 2-methylquinolines was successfully developed by condensation of anilines with vinyl ethers in the presence of catalytic amount of iodine. Modification of both pyridine and benzene moieties was easily achieved by changing only the vinyl ether and aniline. In this reaction, the iodine species was revealed to show dual behavior; molecular iodine serves as an oxidant, while its reduced form, hydrogen iodide, activates the vinyl ether. The redox reaction between these iodine species enables the use of a catalytic amount of iodine in this synthetic method.

p-TsOH-promoted synthesis of (E)-6-phenyl-7-styryl-5,6-dihydrodibenzo[b,h][1,6]naphthyridines via cascade intramolecular aza-Michael addition/Friedlander condensation of 2′-aminochalcones in a SDS/H2O system

p-TsOH-promoted one-pot cascade synthesis of novel (E)-6-phenyl-7-styryl-5,6-dihydrodibenzo[b,h][1,6]naphthyridines via homodimerization of 2′-aminochalcones has been developed in a SDS/H₂O system.

Synthesis of polysubstituted quinolines via transition-metal-free oxidative cycloisomerization of o-cinnamylanilines

An efficient synthesis of 2-aryl 4-substituted quinolines from stable and readily available o-cinnamylanilines, prepared from anilines and cinnamylalcohols, has been developed. The reaction occurred via a regioselective 6-endo-trig intramolecular oxidative cyclization using KO(t)Bu as a mediator and DMSO as an oxidant at rt. The reaction showed a broad substrate scope with good to excellent yields.

Friedländer annulation: scope and limitations of metal salt Lewis acid catalysts in selectivity control for the synthesis of functionalised quinolines

In(OTf)₃ is the most effective catalyst among metal halides, tetrafluoroborates, perchlorates, and triflates for Friedländer quinoline synthesis in 75–92% yields.