Search Results (121)

This study introduces an efficient and sustainable catalytic system utilizing cobalt ferrite nanoparticles (CoFe₂O₄-NPs) for the synthesis of valuable 6-amino-2-oxo-4-phenyl (or 4-chlorophenyl)-1,2,3,4-tetrahydropyrimidine-5-carbonitrile derivatives. Recognizing the limitations of traditional methods for the Biginelli reaction, we thoroughly characterized CoFe₂O₄-NPs, alongside individual iron oxide nanoparticles (Fe₂O₃-NPs) and cobalt oxide nanoparticles (CoO-NPs), using FTIR, XRD, TEM, SEM, XPS, TGA, and BET analysis. These characterizations revealed the unique structural, morphological, and physicochemical properties of CoFe₂O₄-NPs, including an optimized porous structure and significant bimetallic synergy between Fe and Co ions. Catalytic studies demonstrated that CoFe₂O₄-NPs significantly outperformed individual Fe₂O₃-NPs and CoO-NPs under mild conditions. While the latter only catalyzed the Knoevenagel condensation, CoFe₂O₄-NPs uniquely facilitated the complete Biginelli reaction. This superior performance is attributed to the synergistic electronic environment within CoFe₂O₄-NPs, which enhances reactant activation, intermediate stabilization, and proton transfer during the multi-step reaction. This work highlights the potential of CoFe₂O₄-NPs as highly efficient and selective nanocatalysts for synthesizing biologically relevant 1,2,3,4-tetrahydropyrimidines, offering a greener synthetic route in organic chemistry. Full article

A new π-conjugated acceptor–donor–acceptor small molecule, designed for applications in organic solar cells, containing a terthiophene core and indandione- and benzonitrile-based electron-withdrawing units, was synthesized via a multi-step process involving Suzuki–Miyaura cross-coupling and Knoevenagel condensation reactions. The structure was confirmed by NMR spectroscopy, HRMS, and its optoelectronic properties were evaluated by UV–vis spectroscopy and cyclic voltammetry. Full article

In this study, novel fluorescent 5-aryl-2-styryl-3H-indole derivatives were efficiently synthesized from 4-bromophenylhydrazine hydrochloride using the microwave-accelerated one-pot technique, which includes Fischer synthesis, Suzuki cross-coupling, and Knoevenagel condensation. The structural assignments of the synthesized compounds were based on ¹H, ¹³C, ¹⁵N, and ¹⁹F NMR; IR spectroscopy; and HRMS spectral data. The optical properties of the newly obtained styryl-indole dyes were studied using UV-vis and fluorescence spectroscopy, which clearly demonstrated that the derivatives substituted with electron-donating or -withdrawing groups exhibited varying emission shifts and quantum yields ranging from negligible to high. Full article

In the present work, we report the synthesis and characterization of 2-(4-(diphenylamino)benzylidene) malononitrile (DPAM) via a piperidine-catalyzed Knoevenagel condensation reaction. Two distinct crystal forms (A-1 and A-2) of this product were obtained by controlling the crystallization conditions, exhibiting orthorhombic and monoclinic crystal systems, respectively. Single-crystal X-ray diffraction revealed that both forms exhibited highly twisted benzene rings, which suppressed exciplex or excimer formation, enhancing luminescence. Crystal A-1, with a higher density, showed stronger hydrogen bonding and more rigid molecular packing, while A-2, with a lower density, exhibited weaker π–π interactions. Both crystals demonstrated high thermal stability. Notably, the A-2 crystal displayed a mechanochromic behavior: grinding or applying pressure induced a structural transformation into A-1, accompanied by a fluorescence shift from red to yellow. This transformation was attributed to increased steric hindrance and changes in molecular packing. This study highlights the relationship between crystal structure and optoelectronic properties, offering insights into the design of organic crystalline materials for applications in pressure sensing, anti-counterfeiting, and information encryption. Full article

The use of organo-catalysis in continuous-flow reactor systems is gaining attention in medicinal chemistry due to its cost-effectiveness and reduced chemical waste. In this study, bioactive curcumin (CUM) derivatives were synthesized in a continuously operated microfluidic reactor (MFR), using piperidine-based polymeric networks as catalysts. Piperidine methacrylate and piperidine acrylate were synthesized and subsequently copolymerized with complementary monomers (MMA or DMAA) and crosslinkers (EGDMA or MBAM) via photopolymerization, yielding different polymeric networks. Initially, batch reactions were optimized for the organo-catalytic Knoevenagel condensation between CUM and 4-nitrobenzaldehyde, under various conditions, in the presence of polymer networks. Conversion was assessed using offline ¹H NMR spectroscopy, revealing an increase in conversion with enhanced swelling properties of the polymer networks, which facilitated greater accessibility of catalytic sites. In continuous-flow MFR experiments, optimized polymer gel dots exhibited superior catalytic performance, achieving a conversion of up to 72%, compared to other compositions. This improvement was attributed to the enhanced swelling in the reaction mixture (DMSO/methanol, 7:3 v/v) at 40 °C over 72 h. Furthermore, the MFR system enabled the efficient synthesis of a series of CUM derivatives, demonstrating significantly higher conversion rates than traditional batch reactions. Notably, while batch reactions required 90% catalyst loading in the gel, the MFR system achieved a comparable or superior performance with only 50% catalyst, resulting in a higher turnover number. These findings underscore the advantages of continuous-flow organo-catalysis in enhancing catalytic efficiency and sustainability in organic synthesis. Full article

Calcium and barium carbonates were synthesized via biologically induced mineralization using Bacillus subtilis. The biogenic materials were characterized by using infrared and Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and powder X-ray diffraction. These biogenic carbonates were then tested as basic heterogenous catalysts for the solvent-free Knoevenagel reaction between 5-HMF derivatives and active methylene compounds, producing 3-(furan-2-yl)acrylonitrile derivatives in 71–87% yields. Optimal catalytic performance was achieved with a 50:50 Ca:Ba ratio, attributed to the synergistic interaction between baritocalcite and vaterite, which enhances the availability of active basic sites and surface interactions. This method offers operational simplicity, reduced reaction times, good yields, excellent (E)-selectivity, and minimal catalyst loading. Full article

In this work we present, a kinetic study of the Knoevenagel condensation reaction between 5-methoxy-1-tetralone and glyoxylic acid, catalyzed by sulfuric acid, to produce (E)-2-(5-methoxy-1-oxo-3,4-dihydronaphthalen-2(1H)-ylidene)acetic acid. The reaction was carried out in a batch system at 400 rpm for 24 h at temperatures of 75, 80 and 85 °C. The yields obtained at these temperatures were 90.30, 93.75 and 94.16%, respectively. The reaction was monitored by TLC and HPLC. For the kinetic analysis, three mathematical methods were used: integral, differential and non-linear regression. The results showed an excellent fit of the experimental data to the pseudo-first-order kinetic model. Full article

In this paper, a novel, cost-effective, and green methodology has been investigated for the preparation of cobalt (II) nanoparticles supported on a nanodiamond-carbon-structure grafted polyethyleneimine@folic acid (ND-g-PEI@FA@Co(II)) nanocomposite. Some of the physicochemical characteristics of the synthesized efficient heterogeneous nanocatalyst, including bond formation and functional groups, percentage of elements, crystalline phase, and surface morphology were studied using techniques such as Fourier transform infrared spectroscopy (FT-IR), Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). Following the principles of green chemistry, this nanocatalyst has been used in the production of 5-substituted 1H-tetrazole derivatives using different benzaldehyde derivatives, sodium azide, and malononitrile agents in ethanol eco-friendly solvent with high efficiency. The mechanism of tetrazole synthesis is carried out through cascade condensations, such as Knoevenagel condensation, 1,3-dipolar cycloaddition, and tautomerization reactions. The main advantages of the ND-g-PEI@FA@Co(II) nanocatalyst include facile preparation, easy separation, minimal consumption of catalyst for a multicomponent reaction (MCR), the use of cheap and recyclable materials, excellent product yield, and reusability up to four times with good efficiency. The substrate used in this heterogeneous catalyst (ND) with appropriate thermal stability, abundant availability in large quantities, and non-toxicity are prominent features of the synthesized nanocomposite. Full article

Tetronic acid, a five-membered heterocyclic moiety present in various natural products, has emerged as a significant building block for many pharmaceutically active compounds. In this study, a novel protocol for the synthesis of the bis-tetronic acid 3,3′-((4-methoxyphenyl)methylene)bis(4-hydroxyfuran-2(5H)-one) (3) via a domino Knoevenagel–Michael reaction is presented. The natural deep eutectic solvent L-proline/glycerol 1:2 molar ratio was utilized as a solvent and catalyst, while the reaction was further promoted via microwave irradiation, providing the desired product in high yield (83%). The solvent was successfully recycled and reused up to three times. Full article

Our novel binuclear complex-anchored Ru(III) catalyst, designed and assembled by sonicating 2,2′-(4,6-dihydroxy-1,3-phenylene)bis(1H-benzo[d]imidazole-4-carboxylic acid), Ru(DMSO)₄Cl₂ and 4-methylpyridine, demonstrates remarkable efficiency and selectivity. It promotes one-pot reactions, including active methylenes and benzyl alcohols in water, via a tandem aerobic oxidation/Knoevenagel condensation process, yielding benzylidene malononitrile in excellent yields. The catalyst’s ability to oxidize benzyl alcohols to aldehydes, which then undergo Knoevenagel condensation with active methylenes, makes it a multifunctional catalyst. Notably, the catalyst can be successfully retrieved and recycled for five successive rounds with no significant decrease in catalytic efficiency. The ICP study showed that no catalyst leaching was observed, indicating that the designed catalyst is indeed heterogeneous. The Ru catalyst outperformed other documented catalysts in terms of lower dose, shorter duration, decreased working temperature, and the absence of dangerous additives. This demonstrates the catalyst’s robustness and sustainability, making it a promising candidate for future organic conversions and industrial uses. Full article

The grafting of trialkoxysilanes is the most common method for the surface functionalization of silica gel, and it is usually carried out in the presence of toluene or other solvents such as acetonitrile or acetone. Here, we replaced these solvents with alcohols to afford silica materials containing alkoxy groups linked to the silicon atom. The grafting of N,N-dimethyl-3-amino- or 3-amino-propyltrimethoxysilane was carried out in the presence of several alcohols containing an unsubstituted alkyl chain (C7 and C14), a PEG functionalized chain, or an amino-substituted chain (N,N-dimethylamino, pyridyl). Materials were characterized via solid-state ¹³C- and ²⁹Si CPMAS NMR and thermogravimetric analysis to prove that alcohols are not “innocent” solvents but take part in the reaction and lead to [RSi(OR¹)-(OSi)₂] systems where the OR¹ group proceeds from the alcohol used in the synthesis. As a proof of concept, we briefly studied the catalytic activity of some of these materials with the aim of showing how different modifications can influence the course of a selected reaction. Finally, a quaternary ammonium salt (QAS)-based silica was prepared containing both an alkyl-QAS and an alkoxy-QAS linked to silicon atoms. This could represent an interesting approach for the development of new antifouling-based materials and, overall, the described strategy could be useful for the preparation of new organosilica materials. Full article

In this paper, two aggregation-induced emission (AIE) chiral fluorescent materials, S-1 and S-2, were synthesized. The two materials are based on BINOL and H₈-BINOL backbones, respectively, and large electron-absorbing groups are attached to the chiral backbones through the Knoevenagel reaction. At the same time, the CD signals of these two chiral fluorescent materials are gradually weakened (f_w gradually increases) as they continue to aggregate. However, S-2 underwent a flip-flop from a negative to positive chiral CD signal at f_w ≥ 90. And both materials also showed significant enantioselective recognition of lysine, demonstrating their potential as novel chiral fluorescent probes. Among them, the enantioselective fluorescence enhancement ratios (ef) of S-1 and S-2 for lysine were 10.0 and 10.3, respectively, while different degrees of blue shifts were produced by the ICT mechanism during the recognition process. In addition, the self-assembled morphology of the two nanomaterials is different; S-1 comprises hollow-core vesicles that are more likely to aggregate to form larger self-assembled vesicles, whereas S-2 is a solid block structure. When L/D-lysine was added alone, the morphology of S-1 was more distinctly different compared to S-2. With the addition of L-lysine, S-1 was dispersed and regularly spherical, whereas with the addition of D-lysine, S-1 itself remained in the form of aggregated large vesicles. This suggests that both S-1 and S-2 are important in the fields of chiral optics, chiral recognition, and nanoscale self-assembly. Full article

The magnetically recoverable heterogeneous Fe₂O₃@cellulose@Mn nanocomposite was synthesized by a stepwise fabrication of Mn nanoparticles on cellulose-modified magnetic Fe₂O₃ nanocomposites, and the morphology of the nanocomposite was characterized through advanced spectroscopic techniques. This nanocomposite was investigated as a heterogeneous catalyst for the synthesis of medicinally important tetrazole derivatives through Knoevenagel condensation between aromatic/heteroaromatic aldehyde and malononitrile followed by [3+2] cycloaddition reaction with sodium azide. Thirteen potent (E)-1-aryl-2-(1H-tetrazol-5-yl)acrylonitrile derivatives are reported in this paper with very high yields (up to 98%) and with excellent purity (as crystals) in a very short period (3 min @ 120 W) using microwave irradiation. The present procedure offers several advantages over recent protocols, including minimal catalyst loading, quick reaction time, and the utilization of an eco-friendly solvent. Furthermore, the synthesized (E)-1-aryl-2-(1H-tetrazol-5-yl)acrylonitrile derivatives (4b, 4c, and 4m) are shown to have excellent resistance against various fungal strains over bacterial strains as compared to the standard drugs Cefixime (4 μg/mL) and Fluconazole (2 μg/mL). Full article

Three small donor molecule materials (S1, S2, S3) based on dithiophene [2,3-d:2′,3′-d′]dithiophene [1,2-b:4,5-b′]dithiophene (DTBDT) utilized in this study were synthesized using the Vilsmeier–Haack reaction, traditional Stille coupling, and Knoevenagel condensation. Then, a variety of characterization methods were applied to study the differences in optical properties and photovoltaic devices among the three. By synthesizing S2 using a thiophene π-bridge based on S1, the blue shift in ultraviolet absorption can be enhanced, the band gap and energy level can be reduced, the open circuit voltage (V_OC) can be increased to 0.75 V using the S2:Y6 device, and a power conversion efficiency (PCE) of 3% can be achieved. Also, after developing the device using Y6, S3 introduced the alkyl chain of thiophene π-bridge to S2, which improved the solubility of tiny donor molecules, achieved the maximum short-circuit current (J_SC = 10.59 mA/cm²), filling factor (FF = 49.72%), and PCE (4.25%). Thus, a viable option for future design and synthesis of small donor molecule materials is to incorporate thiophene π-bridges into these materials, along with alkyl chains, in order to enhance the device’s morphology and charge transfer behavior. Full article