H5BW12O40-Catalyzed syntheses of 1,4-dihydropyridines and polyhydroquinolines via Hantzsch reaction: Joint experimental and computational studies

Construction of 1,4-Dihydropyridines: The Evolution of C4 Source

The field of cascade cyclization for the construction of 1,4-dihydropyridines (1,4-DHPs) has been continuously expanding during the last decades because of their broad-spectrum biological and synthetic importance. To date, many methods have been developed, mainly including the Hantzsch reaction, Hantzsch-like reaction and newly developed cascade cyclization, in which various synthons have been successively developed as C4 sources of 1,4-DHPs. This review presents the cascade cyclization synthesis strategy for the construction of 1,4-DHPs according to various C4 sources from carbonyl compounds, alkenyl fragments, alcohols, aliphatic amines, glycines and other C4 sources.

Tandem Protocol of Hexahydroquinoline Synthesis Using [H2-DABCO][HSO4]2 Ionic Liquid as a Green Catalyst at Room Temperature

Green, eco-benign, and sustainable synthesis is paramount in present chemistry. Here, a facile, efficient, and [H₂-DABCO][HSO₄]₂ ionic-liquid-catalyzed one-pot multicomponent synthesis of hexahydroquinolines was reported under ambient reaction conditions. The reaction of 1,3-dicarbonyls, malononitrile, and ammonium acetate with various aldehydes in the presence of an ionic liquid catalyst and EtOH solvent at room temperature afforded excellent yields (76-100%) of hexahydroquinolines under a short reaction time (5-15 min). Mild reaction conditions, broad substrate scope (28 derivatives), and column-chromatography-free synthesis with excellent catalytic efficiency and good recyclability rendered this protocol superior and practical. The greenness of the present method was assessed through eco-score and E-factor. The significant results in gram-scale synthetic conditions validate its applicability in industries as well as academia in the near future.

Ionic liquid-loaded triazine-based magnetic nanoparticles for promoting multicomponent reaction

A novel hybrid magnetic ionic-liquid as a heterogeneous catalyst was synthesized by hybridization of imidazolium based-ionic liquid onto the nitrogen rich magnetic nanocomposite. The resulting catalyst (n-Fe₃O₄@SiO₂-TA-SO₃H IL) has two advantages besides recyclability: (i) high capacity of functional-SO₃H group with imidazolium-IL cation for promoting symmetric and asymmetric Hantzsch reaction and (ii) easy recovery. Caused by the polymeric and magnetic nature of the n-Fe₃O₄@SiO₂-TA-SO₃H IL, large quantities of acidic groups were bound to the n-Fe₃O₄@SiO₂-TA surface, which reduced the catalyst mass applied to the catalytic reaction. Moreover, superior catalytic performance and outstanding recyclability of n-Fe₃O₄@SiO₂-TA-SO₃H IL in mild condition make this method a green pathway for manufacture of satisfactory chemicals.

Direction of theoretical and experimental investigation into the mechanism of n-HA/Si-PA-SC@Ag as a bio-based heterogeneous catalyst in the reduction reactions

In the present study, a natural-based heterogeneous catalyst is synthesized. For this purpose, nano-hydroxyapatite (n-HA) is prepared, silica-modified and functionalized with phthalimide. Finally, Ag²⁺ was immobilized onto n-HA/Si-PA-SC and reduced to Ag nanoparticles by Bellis perennis flowers extract. n-HA/Si-PA-SC@Ag characterized by TGA, FTIR, SEM/EDX, XRD, TEM, BET and ICP-AES techniques. Moreover, metal-ligand interactions in n-HA/Si-PA-SC@Ag complex models were assessed to make a quantitative representation for the immobilization behavior of Ag NPs on the surface of n-HA/Si-PA-SC through quantum chemistry computations. Furthermore, the performance of n-HA/Si-PA-SC@Ag was studied in the nitroarene, methylene blue and congo red reductions. Finally, the recyclability study as well as Ag-leaching verified that, n-HA/Si-PA-SC@Ag was stable and reused-up to four times without losing its activity.

MOF/POM hybrids as catalysts for organic transformations

Insertion of molecular metal oxides, e.g. polyoxometalates (POMs), into metal-organic frameworks (MOFs) opens up new research opportunities in various fields, particularly in catalysis. POM/MOF composites have strong acidity, oxygen-rich surface, and redox capacity due to typical characteristics of POMs and the large surface area, highly organized structures, tunable pore size, and shape are due to MOFs. Such hybrid materials have gained a lot of attention due to astonishing structural features, and hence have potential applications in organic catalysis, sorption and separation, proton conduction, magnetism, lithium-ion batteries, supercapacitors, electrochemistry, medicine, bio-fuel, and so on. The exceptional chemical and physical characteristics of POMOFs make them useful as catalysts in simple organic transformations with high capacity and selectivity. Here, the thorough catalytic study starts with a brief introduction related to POMs and MOFs, and is followed by the synthetic strategies and applications of these materials in several catalytic organic transformations. Furthermore, catalytic conversions like oxidation, condensation, esterification, and some other types of catalytic reactions including photocatalytic reactions are discussed in length with their plausible catalytic mechanisms. The disadvantages of the POMOFs and difficulties faced in the field have also been explored briefly from our perspectives.

Catalytic Approaches to Multicomponent Reactions: A Critical Review and Perspectives on the Roles of Catalysis

In this review, we comprehensively describe catalyzed multicomponent reactions (MCRs) and the multiple roles of catalysis combined with key parameters to perform these transformations. Besides improving yields and shortening reaction times, catalysis is vital to achieving greener protocols and to furthering the MCR field of research. Considering that MCRs typically have two or more possible reaction pathways to explain the transformation, catalysis is essential for selecting a reaction route and avoiding byproduct formation. Key parameters, such as temperature, catalyst amounts and reagent quantities, were analyzed. Solvent effects, which are likely the most neglected topic in MCRs, as well as their combined roles with catalysis, are critically discussed. Stereocontrolled MCRs, rarely observed without the presence of a catalytic system, are also presented and discussed in this review. Perspectives on the use of catalytic systems for improved and greener MCRs are finally presented.

Recent Progresses in the Multicomponent Synthesis of Dihydropyridines by Applying Sustainable Catalysts Under Green Conditions

The synthesis of dihydropyridines, valuable molecules with diverse therapeutic properties, using eco-friendly heterogeneous catalysts as a green alternative received significant consideration. By selecting appropriate precursors, these compounds can be readily modified to induce the desired properties in the target product. This review focused on synthesising diverse dihydropyridine derivatives in single-pot reactions using magnetic, silica, and zirconium-based heterogeneous catalytic systems. The monograph describes preparation techniques for various catalyst materials in detail. It covers facile and benign magnetic, silica, zirconium-based, and ionic liquid catalysts, exhibiting significant efficacy and consistently facilitating excellent yields in short reaction times and in a cost-effective way. Most of the designated protocols employ Hantzsch reactions involving substituted aldehydes, active methylene compounds, and ammonium acetate. These reactions presumably follow Knoevenagel condensation followed by Michael addition and intra-molecular cyclisation. The multicomponent one-pot protocols using green catalysts and solvents have admirably increased the product selectivity and yields while minimising the reaction time. These sustainable catalyst materials retain their viability for several cycles reducing the expenditure are eco-friendly.

Preparation, Antibacterial Activity, and Catalytic Application of Magnetic Graphene Oxide-Fucoidan in the Synthesis of 1,4-Dihydropyridines and Polyhydroquinolines

Polymer-coated magnetic nanoparticles are emerging as a useful tool for a variety of applications, including catalysis. In the present study, fucoidan-coated magnetic graphene oxide was synthesized using a natural sulfated polysaccharide. The prepared BaFe12 O19 @GO@Fu (Fu=fucoidan, GO=graphene oxide) was characterized using Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) analysis, vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), Raman spectroscopy, and X-ray diffraction (XRD). The catalytic proficiency of BaFe12 O19 @GO@Fu was investigated in the synthesis of 1,4-dihydropyridine and polyhydroquinoline derivatives. Excellent turnover numbers (TON) and turnover frequencies (TOF) (6330 and 25320 h-1 ) testify to the high efficiency of the catalyst. Moreover, the antimicrobial activity of BaFe12 O19 @GO@Fu was evaluated against Escherichia coli (E. coli), and Staphylococcus aureus (S. aureus) through the Agar well diffusion method, indicating that BaFe12 O19 @GO@Fu has antibacterial activity against S. aureus.

Full Kinetics and Mechanism Investigation for Generating 4-Substituted 1, 4- Dihydropyridine Derivatives in the Presence of Green Catalyst and Aqueous Medium: Experimental Procedure

AIMS AND OBJECTIVE

The main objective of the kinetic investigation of the reaction between ethyl acetoacetate 1, ammoniumacetat 2, dimedone 3, and diverse substitutions of benzaldehyde 4-X, (X= H, NO₂, CN, CF₃, Cl, CH (CH₃)₂, CH₃, OCH₃, OCH₃, and OH) for generating 4-substituted 1, 4-dihydropyridine derivatives (product 5) was to recognize the most realistic reaction mechanism. The layout of the reaction mechanism was studied kinetically via a UV-visible spectrophotometry approach.

MATERIALS AND METHODS

Among the various mechanisms, only mechanism1 (path1) involving 12 steps was recognized as a dominant mechanism (path₁). Herein, the reactions between 1 and 2 (k_obs= 814.04 M^-1.min^-1) and also between 3 and 4-H (k_obs= 151.18 M^-1.min^-1) can be accepted as the first and second steps (step₁ and step₂) of the reaction mechanism, respectively. Amongst all steps, only step9 of the dominant mechanism (path₁) comprised substituent groups (X) near the reaction center.

RESULTS AND DISCUSSION

Para electron-withdrawing or donating groups on the compound 4-X increased the rate of the reaction 4 times more or decreased 8.7 times less than the benzaldehyde alone. So, this step is sensitive for monitoring any small or huge changes in the reaction rate. Accordingly, step9 is the rate-determining step of the reaction mechanism (path₁).

CONCLUSION

The recent result is in agreement with the Hammett description of an excellent dual substituent factor (r = 0.990) and positive value of reaction constant (ρ= +0.9502), which confirms that both the resonance and inductive effects "altogether" contribute to the reaction center of step9 in the dominant mechanism (path₁).

Synthesis, characterization and cytotoxicity evaluation of a novel magnetic nanocomposite with iron oxide deposited on cellulose nanofibers with nickel (Fe3O4@NFC@ONSM-Ni)

A heterogeneous, magnetically recoverable nanocomposite, Fe3O4@NFC@ONSM-Ni(ii) was prepared by immobilization of a novel Ni(ii) Schiff base complex on Fe3O4@NFC nanoparticles followed by treatment with melamine. This trinuclear catalyst has been characterized using several analytical techniques including FT-IR, TEM, Fe-SEM, EDX, DLS, ICP, TGA, VSM, and XRD. It was used as an efficient catalyst for one-pot solvent-free synthesis of 1,4-dihydropyridine and poly-hydro quinoline derivatives through Hantzsch reaction. This catalyst showed remarkable advantage over previously reported catalysts due to suitable conditions, short reaction time, high efficiency and lower catalyst load and timely recovery of the magnetic catalyst. Moreover, the effects of Fe3O4@NFC@ONSM-Ni(ii) nanoparticles on the in vitro proliferation of human leukemia cell line (k562) and human breast cancer cells (MDA-MB-231) were investigated. The results of MTT and Hochest assays suggested that the nanoparticles could effectively inhibit the proliferation of these cancer cells in a time- and concentration-dependent manner.

Green synthesis and characterization of novel Mn-MOFs with catalytic and antibacterial potentials

The synthesis and characterization of novel Mn-MOF nanostructures (UoB-4) with high performance as catalysts and antibacterial agents.