V 2 O 5 /ZrO 2 as an efficient reusable catalyst for the facile, green, one-pot synthesis of novel functionalized 1,4-dihydropyridine derivatives

Montmorillonite K-10 catalyzed synthesis of Hantzsch dihydropyridine derivatives from methyl arenes via in situ generated ammonia under microwave irradiation in neat conditions

An expeditious, efficient, and environmentally friendly approach has been established for the synthesis of diverse Hantzsch 1,4-dihydropyridine derivatives utilizing montmorillonite K-10 as a catalyst in solvent-free conditions. The procedure entails the reaction of methyl arynes as a sustainable surrogate of aryl aldehydes, active methylene compounds, and urea hydrogen peroxide (UHP) as an oxidising agent as well as a source of ammonia under microwave irradiation, facilitated by montmorillonite K-10.

AlCl3@ZnO nanostructured material: an efficient green catalyst for the one-pot solvent-free synthesis of 1,4-dihydropyridines

AlCl3-loaded ZnO nanoparticles have been explored as an efficient catalyst for 1,4-dihydropyridine synthesis under ambient temperature and solvent-free conditions. For this purpose, ZnO nanoparticles were synthesized by a simple solution-based precipitation technique using a stoichiometric amount of zinc sulfate and oxalic acid. The AlCl3@ZnO nanocrystalline catalyst was prepared by loading 20% AlCl3 on ZnO nanoparticles by a simple wet-impregnation technique. This catalyst efficiently performed Hantzsch pyridine reactions with various aromatic aldehydes, ethyl acetoacetate and ammonium acetate. The nanostructured AlCl3-loaded ZnO catalyst was characterized by UV-DRS, XRD, FESEM, EDS, FETEM-STEM-EDS and XPS techniques. The comprehensive characterization reveals the formation of AlCl3-loaded ZnO catalysts with an average particle size of 70-80 nm. The loading of AlCl3 on the ZnO surface was confirmed by minor shifts in the XPS and XRD peaks. FETEM-STEM-EDS also indicates reasonable AlCl3 loading on ZnO nanoparticles. The 20% AlCl3-loaded ZnO nanocatalyst (AlCl3@ZnO) confers 92% yield for the synthesis of 1,4-dihydropyridine under solvent-free and ambient temperature conditions. The synthesized 1,4-dihydropyridines were characterized by 1H-NMR, 13C-NMR, HRMS and FT-IR spectroscopic techniques. The reported catalyst is highly efficient, environmentally friendly and could become an alternative to homogenous and heterogenous catalytic reactions.

Water compatible silica supported iron trifluoroacetate and trichloroacetate: as prominent and recyclable Lewis acid catalysts for solvent-free green synthesis of hexahydroquinoline-3-carboxamides

Silica supported iron trifluoroacetate and iron trichloroacetate green Lewis acid catalysts were developed by a novel, cheap, environment-friendly approach and utilized in the synthesis of hexahydroquinoline-3-carboxamide derivatives. The structure and morphology of the prepared Lewis acid catalysts were studied by FTIR, PXRD, FE-SEM, HR-TEM, EDX, BET, TGA and NH3-TPD techniques. The present catalysts shows maximum conversion efficiency in hexahydroquinoline-3-carboxamide derivatives synthesis at 70 °C in solvent free reaction condition with best product yield in a short reaction time. Both catalysts are reusable and simple to recover, and perform meritoriously in water as well as in a variety of organic solvents. The key advantages of the current synthetic route are permitting of a variety of functional groups, quick reaction time, high product yield, mild reaction condition, recyclability of catalyst and solvent-free green synthesis. This makes it more convenient, economic and environmentally beneficial.

Research progress of vanadium pentoxide photocatalytic materials

Photocatalytic reactions convert solar energy into chemical energy through a clean and green reaction process. Photocatalytic technology based on semiconductor materials provides us with a new idea in energy utilization and environmental governance. It was found that vanadium pentoxide (V₂O₅) has a narrow band gap, wide response range in the visible region, high oxygen density in the V₂O₅ lattice, high oxidation state of V⁵⁺, small energy requirement, and superior catalytic activity in partial oxidation. Therefore, the utilization rate of sunlight and photocatalytic oxidation can be greatly improved using V₂O₅ materials. However, the narrow band gap of V₂O₅ also makes it easier for the photogenerated electrons and holes to recombine in the excited state, and the stored energy is instantly consumed by carrier recombination. Therefore, how to promote the carrier separation of V₂O₅ and improve the photocatalytic efficiency are the key problems to be solved. Herein, several methods to improve the photocatalytic performance of V₂O₅ are reviewed, including metallic ion doping, non-metallic ion doping, semiconductor recombination, and noble metal deposition. Finally, it is suggested that future research directions should focus on a variety of modification methods simultaneously to promote photocatalytic efficiency and lower the cost, which will enable V₂O₅ to have a broad development prospect in the field of photocatalysis.

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.

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).

Diversified Synthetic Pathway of 1, 4-Dihydropyridines: A Class of Pharmacologically Important Molecules

The current review discusses the different synthetic pathways for one of the most important and interesting heterocyclic ring systems, 1,4-dihydropyridine. This cyclic system depicts diverse pharmacological action on several receptors, channels, and enzymes. Dihydropyridine moiety plays an important role in several calcium-channel blockers. Moreover, it has been exploited for the treatment of a variety of cardiovascular diseases due to its potential antihypertensive, anti-angina, vasodilator, and cardiac depressant activities. Furthermore, it also shows antibacterial, anticancer, anti-leishmanial, anticoagulant, anticonvulsant, anti-tubercular, antioxidant, antiulcer, and neuroprotective properties. Several reports have demonstrated dihydropyridine derivatives as a potentiator of cystic fibrosis transmembrane conductance regulator protein, potent antimalarial agent and HIV-1 protease inhibitor. Herein, we have briefly reviewed different novel chemistry and the synthesis of 1,4-dihydropyridine.

A Facile and Catalyst-Free Microwave-Promoted Multicomponent Reaction for the Synthesis of Functionalised 1,4-Dihydropyridines With Superb Selectivity and Yields

We report a highly efficient green protocol for developing a novel library of 1,2,4-triazole-tagged 1,4-dihydropyridine analogs through the one-pot process from the four-component fusion of the 1H-1,2,4-triazol-3-amine with different chosen aldehydes, diethyl acetylenedicarboxylate, and active methylene compounds in a water medium under microwave irradiation and catalyst-free conditions. Excellent yields (94-97%) of the target products were achieved with high selectivity with a short reaction time (<12 min) at room temperature. The structures of the synthesized pyrimidine analogs were established by NMR and HRMS spectroscopic analysis. Simple workup, impressive yields, no column chromatography, green solvent, rapid reaction, and excellent functional group tolerance are the benefits of this protocol.

Green synthesis and characterisation of novel [1,3,4]thiadiazolo/benzo[4,5]thiazolo[3,2-a]pyrimidines via multicomponent reaction using vanadium oxide loaded on fluorapatite as a robust and sustainable catalyst

We synthesised materials with different loadings of vanadia on fluorapatite (V2O5/FAp), fully characterised their structural properties using various spectral techniques including TEM, BET, XRD, FT-IR, SEM and EDX and assessed their prowess as catalysts. The 2.5% V2O5/FAp exhibited excellent activity for the synthesis of novel [1,3,4]thiadiazolo[3,2-a]pyrimidines and benzo[4,5]thiazolo[3,2-a]pyrimidines. The one-pot three-component fusion reaction between chosen substrates of 1,3,4-thiadiazole-amines or 2-amino-benzothiazole, aldehydes and active methylene compounds in ethanol solvent at room temperature gave an excellent yield of products (90-97%) in a swift reaction (25-30 min). The advantages of this protocol are rapid synthesis, mild reaction conditions, green solvent, easy work-up, eco-friendliness, reusability of catalyst and no need for column chromatography.

Dihydropyridines as potential α-amylase and α-glucosidase inhibitors: Synthesis, in vitro and in silico studies

Dihydropyridine derivatives 1-31 were synthesized via one-pot solvent free condition and screened for in vitro against α-amylase and α-glucosidase enzyme. The synthetic derivatives 1-31 showed good α-amylase inhibition in the range of IC₅₀ = 2.21 ± 0.06-9.97 ± 0.08 µM, as compared to the standard drug acarbose (IC₅₀ = 2.01 ± 0.1 µM) and α-glucosidase inhibition in the range of IC₅₀ = 2.31 ± 0.09-9.9 ± 0.1 µM as compared to standard acarbose (IC₅₀ = 2.07 ± 0.1 µM), respectively. To determine the mode of binding interactions of synthetic molecules with active sites of enzyme, molecular docking studies were also performed. Different spectroscopic techniques such as ¹H, ¹³C NMR, EI-MS, and HREI-MS were used to characterize all the synthetic compounds.

Efficient synthesis of novel pyrazole-linked 1,2,4-triazolidine-3-thiones using bismuth on zirconium oxide as a recyclable catalyst in aqueous medium

The Bi₂O₃ loading on ZrO₂ as heterogeneous catalyst was established as an extremely efficient catalyst for the synthesis of a series of novel 5-(1-(2,4-dinitrophenyl)-3-substituted-phenyl-1H-pyrazol-4-yl)-1,2,4-triazolidine-3-thione derivatives (3a-o) with high yields (90-96%) by reaction of 1-(2,4-dinitrophenyl)-3-substituted-phenyl-1H-pyrazole-4-carbaldehydes and thiosemicarbazide using water as a greener solvent at 80 °C within 30-45 min. Materials with different percentages of Bi₂O₃ on ZrO₂ were prepared by simple wet impregnation method. The synthesized material has been characterized by various techniques (XRD, TEM, SEM, BET). 2.5% Bi₂O₃/ZrO₂ proved superior catalyst. The Bi₂O₃/ZrO₂ catalyst is easily recoverable and reused up to sixth run with no loss of activity. Excellent yields, short reaction time, avoidance of hazardous solvents, and no need for chromatographic purifications are the proven advantages.

Ag₂O on ZrO₂ as a Recyclable Catalyst for Multicomponent Synthesis of Indenopyrimidine Derivatives

We describe the synthesis of silver loaded on zirconia and its use as an efficient catalyst for a one-pot three-component reaction to synthesize 11 indenopyrimidine derivatives, of which 7 are new compounds. The procedure involves substituted benzaldehydes, indane-1,3-dione, and guanidinium hydrochloride, with ethanol as solvent. The proposed green protocol at room temperature is simple and efficient, giving excellent yields (90⁻96%) in short reaction times (<30 min). The protocol works well according to the green chemistry principles with respect to high atom economy, no need for column separation, and reusability of the catalyst, which are attractive features. XRD, TEM, SEM, and BET analysis were used to characterize the catalyst materials.

An efficient and green approach for the synthesis of 2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylates using Bi2O3/ZrO2 as a reusable catalyst

A novel material of bismuth loaded on zirconia (Bi2O3/ZrO2) is synthesized by simple wet-impregnation method and characterized by several techniques (P-XRD, TEM, SEM, BET, etc.). Bi2O3/ZrO2 proved to be a good catalyst for the four-component, one-pot reaction to produce a new series of 2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylate derivatives with excellent yields (91 to 98%) under mild conditions at RT with short reaction times (≈20 min). The structures of the target molecules were confirmed by 1H NMR, 13C NMR, 15N NMR, HRMS and FT-IR. The catalyst is easily separable and can be reused for six cycles without ostensible loss of activity. This method is inexpensive, atom-efficient and no chromatographic separations are needed.

Preparation of a novel palladium catalytic hydrogel based on graphene oxide/chitosan NPs and cellulose nanowhiskers

Pd NPs dispersed on a polysaccharide-based hydrogel as a novel catalyst show high catalytic activity and recyclability for coupling reactions.