A novel and reusable ionically tagged nanomagnetic catalyst: Application for the preparation of 2-amino-6-(2-oxo-2H-chromen-3-yl)-4-arylnicotinonitriles via vinylogous anomeric based oxidation

Greener Syntheses of Coumarin Derivatives Using Magnetic Nanocatalysts: Recent Advances

Coumarins (2H-1-benzopyran-2-ones) are an important group of biological heterocyclic compounds present in various parts of many plant species, encompassing an array of biological and pharmaceutical activities. In view of the importance of coumarins in heterocyclic chemistry and biological sciences and recent advances in the design of magnetic nanocatalysts, we present herein recent developments pertaining to their synthesis exclusively using magnetic nanoparticles, which can be retrieved easily and thus conform to the tenets of greener synthesis. The preparation of various types of coumarins such as Pechmann-based coumarins, bis coumarins, pyranocoumarins, and coumarin derivatives bearing amine moiety, linked to nicotinonitriles, N-coumarin-2-furanone, and pyrrole-linked chromene derivatives using nanocatalysts with a Fe₃O₄ core are described. This review covers the synthetic developments in the recent years 2012-2021 and focuses entirely on the synthesis of coumarins in the presence of magnetic nanocatalysts using greener approaches such as solvent-free conditions or deploying alternative activation methods, namely microwave or ultrasound irradiation.

A magnetic porous organic polymer: catalytic application in the synthesis of hybrid pyridines with indole, triazole and sulfonamide moieties

Herein, the synthesis and characterization of a triazine-based magnetic ionic porous organic polymer are reported. The structure, morphology, and components of the prepared structure have been investigated with several spectroscopic and microscopic techniques such as FT-IR, EDX, elemental mapping, TGA/DTA, SEM, TEM, VSM, and BET analysis. Also, catalytic application of the prepared triazine-based magnetic ionic porous organic polymer was investigated for the synthesis of hybrid pyridine derivatives bearing indole, triazole and sulfonamide groups. Furthermore, the prepared hybrid pyridine systems were characterized by FT-IR, 1H NMR, 13C NMR and mass analysis. A cooperative vinylogous anomeric-based oxidation pathway was suggested for the synthesis of target molecules.

Pd on thermo-responsive composite of silica-coated carbon nanotube and 1-vinyl-3-butylimidazolium-based ionic liquid copolymers as an efficient catalyst for hydrogenation of nitro compounds

In this work, an ionic liquid-containing thermo-responsive heterogeneous catalyst with utility for promoting hydrogenation of nitro-compounds in aqueous media is developed. To prepare the catalyst, silica-coated carbon nanotubes were synthesized and vinyl-functionalized. The resulted compound was then polymerized with 1-viny-3-butylimidazolium bromide and N-isopropylacrylamide. The obtained ionic liquid-containing thermo-responsive composite was palladated via wet-impregnation method to give the final catalyst. Study of the performance of the catalyst confirmed high catalytic activity of the catalyst at temperature above the lower critical solution temperature. Furthermore, the catalyst was highly recyclable and showed negligible Pd leaching upon recycling. Broad substrate scope and selectivity of the catalyst towards reduction of nitro functionality were also confirmed. Furthermore, hot filtration test implied the heterogeneous nature of the catalysis. The comparison of the activity of Pd/CNT-P with some control catalysts approved the importance of hybridization of P and CNT and the presence of ionic liquid for the catalytic activity.

A novel composite of ionic liquid-containing polymer and metal-organic framework as an efficient catalyst for ultrasonic-assisted Knoevenagel condensation

1-Butyl-3-vinylimidazolium chloride was synthesized and polymerized with acrylamide to furnish an ionic liquid-containing polymer, which was then used for the formation of a composite with iron-based metal-organic framework. The resultant composite was characterized with XRD, TGA, FE-SEM, FTIR, EDS and elemental mapping analyses and its catalytic activity was appraised for ultrasonic-assisted Knoevenagel condensation. The results confirmed that the prepared composite could promote the reaction efficiently to furnish the corresponding products in high yields in very short reaction times. Moreover, the composite exhibited high recyclability up to six runs. It was also established that the activity of the composite was higher compared to pristine metal-organic framework or polymer.

Acidic tributyl phosphonium-based ionic liquid: an efficient catalyst for preparation of diverse pyridine systems via a cooperative vinylogous anomeric-based oxidation

Experimental procedure for the synthesis of triaryl pyridines, indolyl pyridines and nicotinonitriles.

Halloysite Nanoclay with High Content of Sulfonic Acid-Based Ionic Liquid: A Novel Catalyst for the Synthesis of Tetrahydrobenzo[b]pyrans

One of the main drawbacks of supported ionic liquids is their low loading and consequently, low activity of the resultant catalysts. To furnish a solution to this issue, a novel heterocyclic ligand with multi imine sites was introduced on the surface of amino-functionalized halloysite support via successive reactions with 2,4,6-trichloro-1,3,5-triazine and 2-aminopyrimidine. Subsequently, the imine sites were transformed to sulfonic acid-based ionic liquids via reaction with 1,4-butanesultone. Using this strategy, high loading of ionic liquid was loaded on halloysite nanoclay. The supported ionic liquid was then characterized with XRD, SEM, TEM, EDS, FTIR, BET, TGA and elemental mapping analysis and utilized as a metal-free Brønsted acid catalyst for promoting one-pot reaction of aldehydes, dimedone and malononitrile to furnish tetrahydrobenzo[b]pyrans. The catalytic tests confirmed high performance of the catalyst. Moreover, the catalyst was stable upon recycling.

Stereoelectronic power of oxygen in control of chemical reactivity: the anomeric effect is not alone

Although carbon is the central element of organic chemistry, oxygen is the central element of stereoelectronic control in organic chemistry. Generally, a molecule with a C-O bond has both a strong donor (a lone pair) and a strong acceptor (e.g., a σ*_C-O orbital), a combination that provides opportunities to influence chemical transformations at both ends of the electron demand spectrum. Oxygen is a stereoelectronic chameleon that adapts to the varying situations in radical, cationic, anionic, and metal-mediated transformations. Arguably, the most historically important stereoelectronic effect is the anomeric effect (AE), i.e., the axial preference of acceptor groups at the anomeric position of sugars. Although AE is generally attributed to hyperconjugative interactions of σ-acceptors with a lone pair at oxygen (negative hyperconjugation), recent literature reports suggested alternative explanations. In this context, it is timely to evaluate the fundamental connections between the AE and a broad variety of O-functional groups. Such connections illustrate the general role of hyperconjugation with oxygen lone pairs in reactivity. Lessons from the AE can be used as the conceptual framework for organizing disjointed observations into a logical body of knowledge. In contrast, neglect of hyperconjugation can be deeply misleading as it removes the stereoelectronic cornerstone on which, as we show in this review, the chemistry of organic oxygen functionalities is largely based. As negative hyperconjugation releases the "underutilized" stereoelectronic power of unshared electrons (the lone pairs) for the stabilization of a developing positive charge, the role of orbital interactions increases when the electronic demand is high and molecules distort from their equilibrium geometries. From this perspective, hyperconjugative anomeric interactions play a unique role in guiding reaction design. In this manuscript, we discuss the reactivity of organic O-functionalities, outline variations in the possible hyperconjugative patterns, and showcase the vast implications of AE for the structure and reactivity. On our journey through a variety of O-containing organic functional groups, from textbook to exotic, we will illustrate how this knowledge can predict chemical reactivity and unlock new useful synthetic transformations.

Synthesis of triarylpyridines with sulfonate and sulfonamide moieties via a cooperative vinylogous anomeric-based oxidation

Herein, novel magnetic nanoparticles with pyridinium bridges namely Fe3O4@SiO2@PCLH-TFA through a multi-step pathway were designed and synthesized. The desired catalyst and its corresponding precursors were characterized with different techniques such as Fourier transform infrared (FT-IR) spectroscopy, 1H NMR, 13C NMR, Mass spectroscopy, energy dispersive X-ray (EDX) analysis, thermogravimetric/derivative thermogravimetry (TG/DTG) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). In addition, the catalytic application of the prepared catalyst in the synthesis of new series of triarylpyridines bearing sulfonate and sulfonamide moieties via a cooperative vinylogous anomeric-based oxidation was highlighted. The current trend revealed that the mentioned catalyst shows high recoverability in the reported synthesis.

Synthesis of new pyridines with sulfonamide moiety via a cooperative vinylogous anomeric-based oxidation mechanism in the presence of a novel quinoline-based dendrimer-like ionic liquid

In the present study, we reported the synthesis of a novel quinoline-based dendrimer-like ionic liquid. After characterization of the mentioned ionic liquid with suitable techniques such as Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX), elemental mapping, thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), its catalytic performance was investigated in the synthesis of new pyridines with sulfonamide moiety via a cooperative vinylogous anomeric-based oxidation mechanism under mild reaction conditions. All target molecules were achieved in short reaction times and high yields.

Magnetically recoverable catalysts for the preparation of pyridine derivatives: an overview

Magnetically recoverable nano-catalysts can be readily separated from the reaction medium using an external magnet. In recent years, chemistry researchers have employed them as catalysts in chemical reactions. The high surface area, simple preparation, and modification are among their major advantages. Pyridine derivatives are an important category of heterocyclic compounds, which show a wide range of excellent biological activities, including IKK-β inhibitors, anti-microbial agents, A2A adenosine receptor antagonists, inhibitors of HIV-1 integrase, anti-tumor, anti-inflammatory, and anti-Parkinsonism. Recently, the catalytic activity of magnetic nanoparticles was investigated in multicomponent reactions in the synthesis of pyridine derivatives, which is discussed in this review.

Magnetically recoverable nano-catalysts can be readily separated from the reaction medium using an external magnet.

Biochar-Based Graphitic Carbon Nitride Adorned with Ionic Liquid Containing Acidic Polymer: A Versatile, Non-Metallic Catalyst for Acid Catalyzed Reaction

A novel biochar-based graphitic carbon nitride was prepared through calcination of Zinnia grandiflora petals and urea. To provide acidic and ionic-liquid functionalities on the prepared carbon, the resultant biochar-based graphitic carbon nitride was vinyl functionalized and polymerized with 2-acrylamido-2-methyl-1-propanesulfonic acid, acrylic acid and the as-prepared 1-vinyl-3-butylimidazolium chloride. The final catalytic system that benefits from both acidic (-COOH and -SO3H) and ionic-liquid functionalities was applied as a versatile, metal-free catalyst for promoting some model acid catalyzed reactions such as Knoevenagel condensation and Biginelli reaction in aqueous media under a very mild reaction condition. The results confirmed high activity of the catalyst. Broad substrate scope and recyclability and stability of the catalyst were other merits of the developed protocols. Comparative experiments also indicated that both acidic and ionic-liquid functionalities on the catalyst participated in the catalysis.

Fabrication of a metal free catalyst for chemical reactions through decoration of chitosan with ionic liquid terminated dendritic moiety

In attempt to develop a biocompatible metal-free catalyst, a dendritic moiety was grown on chitosan through successive reactions with 2,4,6-trichloro-1,3,5-triazine and ethylenediamine. Subsequently, the terminal functional groups of the dendron were decorated with 1-methylimidazolium chloride. The catalyst was characterized with SEM, EDS, TGA, FTIR, XRD and mapping analysis. Then, the catalytic activity of the resultant composite was scrutinized for catalyzing Knoevenagel condensation and synthesis of xanthene derivatives in aqueous media under mild reaction condition. The results confirmed high activity of the catalyst, superior to ionic liquid free counterpart and bare chitosan. This observation was ascribed to the instinct catalytic activity of ionic liquid. Moreover, using control catalysts, it was confirmed that the presence of the dendritic moiety that could increase the content of ionic liquid on the backbone of the catalyst enhanced the catalytic activity.

Synthesis of cobalt tetra-2,3-pyridiniumporphyrazinato with sulfonic acid tags as an efficient catalyst and its application for the synthesis of bicyclic ortho-aminocarbonitriles, cyclohexa-1,3-dienamines and 2-amino-3-cyanopyridines

Cobalt tetra-2,3-pyridiniumporphyrazinato with sulfonic acid tag [Co(TPPASO3H)]Cl was produced and catalyzed the synthesis of ortho-aminocarbonitriles, cyclohexa-1,3-dienamines and 2-amino-3-cyanopyridines. The synthesis of 2-amino-3-cyanopyridines by using [Co(TPPASO3H)]Cl proceeded via a cooperative vinylogous anomeric based oxidation mechanism. [Co(TPPASO3H)]Cl can be recycled and reused six times with a marginal decreasing of its catalytic activity.

A convenient method for synthesis of terpyridines via a cooperative vinylogous anomeric based oxidation

The presented study is the first report of the synthesis of terpyridines in the presence of a nanomagnetic catalyst instead of harmful reagents. Herein, Fe3O4@O2PO2(CH2)2NH3 +CF3CO2 - as a retrievable nanocatalyst with magnetic properties was applied for the multi-component reaction between acetylpyridine derivatives (2 or 3 or 4-isomer), aryl aldehydes and ammonium acetate under conventional heating conditions in the absence of any solvent. The derived terpyridines were obtained with acceptable yields and brief reaction times via a cooperative vinylogous anomeric based oxidation route. Fe3O4@O2PO2(CH2)2NH3 +CF3CO2 - showed a high capability for recovery and reuse in the mentioned reaction.

Synthesis of Metal-Organic Frameworks MIL-101(Cr)-NH2 Containing Phosphorous Acid Functional Groups: Application for the Synthesis of N-Amino-2-pyridone and Pyrano [2,3-c]pyrazole Derivatives via a Cooperative Vinylogous Anomeric-Based Oxidation

In the current paper, we successfully developed and used metal-organic frameworks (MOFs) based on MIL-101(Cr)-NH2 with phosphorus acid functional groups MIL-101(Cr)-N(CH2PO3H2)2. The synthesized metal-organic frameworks (MOFs) as a multi-functional heterogeneous and nanoporous catalyst were used for the synthesis of N-amino-2-pyridone and pyrano [2,3-c]pyrazole derivatives via reaction of ethyl cyanoacetate or ethyl acetoacetate, hydrazine hydrate, malononitrile, and various aldehydes. The final step of the reaction mechanism was preceded by a cooperative vinylogous anomeric-based oxidation. Recycle and reusability of the described catalyst MIL-101(Cr)-N(CH2PO3H2)2 were also investigated.

Ionically Tagged Magnetic Nanoparticles with Urea Linkers: Application for Preparation of 2-Aryl-quinoline-4-carboxylic Acids via an Anomeric-Based Oxidation Mechanism

In this exploration, we reported the design and synthesis of a novel ionically tagged magnetic nanoparticles bearing urea linkers, namely, Fe₃O₄@SiO₂@(CH₂)₃-urea-thiazole sulfonic acid chloride. The structure of the mentioned compound was fully characterized by using several techniques including Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, elemental mapping analysis, thermogravimetric analysis/differential thermal analysis, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometer. In the presence of the novel reusable catalyst, applied starting materials including aryl aldehydes, pyruvic acid, and 1-naphthylamine condensed to afford the desired 2-aryl-quinoline-4-carboxylic acid derivatives via an anomeric-based oxidation pathway under solvent-free conditions.