Efficient Lewis Acid Catalyst Research Articles

Homogeneous Zn(II) salts as efficient Lewis acid catalysts for the esterification of levulinic acid with diols

The valorization of renewable feedstocks to produce biochemicals and biofuels is an essential focus of contemporary research, with non-food crop biomass emerging as a cost-effective and environmentally friendly option. Among the chemicals derived from lignocellulosic biomass, levulinic acid (LAH) is a notable chemical platform due to its versatile applications. This study investigates the eco-friendly esterification of levulinic acid with polyols, catalyzed by zinc(II) species under mild, solvent-free conditions.A comprehensive screening of various zinc(II) species was conducted, to identify the most effective catalyst, ultimately selecting zinc triflate for its performance. The esterification scope was extended to three diols: 1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol. These esters can replace fossil-based chemicals in many emerging sectors, as lubricants and as components in energy storage devices. The reaction conditions were fine-tuned to maximize yield and selectivity, using NMR spectroscopy to monitor the formation of mono- and di-esters and assess reaction profiles. Optimization experiments demonstrated that a catalyst loading of 1.0 %mol and a temperature of 120 °C yielded quantitative conversion within convenient reaction time (2–4 h). The findings highlight the efficiency of simple zinc(II) catalysts in producing levulinate esters with high yields and selectivity under sustainable conditions. Therefore, this research contributes to the development of greener processes to produce valuable chemicals and additives from renewable resources.

A highly efficient Lewis acid catalyst of F-doped activated carbon for acetylene dimerization

Doping carbon-based materials with heteroatoms is considered an effective strategy to enhance their catalytic activity by altering their electronic structure and chemical properties. In this study, fluorine doped activated carbon was synthesized and used in acetylene dimerization reaction. Fluorine has the highest electronegativity (3.98) and can induce neighboring carbon atoms to possess a stronger positive charge, thereby generating Lewis acid sites between the two atoms. The resulting carbon material exhibited abundant Lewis acid sites ensuring the ample exposure and availability of catalytic sites to facilitate notable activity in acetylene dimerization. Theoretical calculations indicated that the introduction of F could help to alleviate the progression of polymers. This research provides a promising approach to the development of solid acid catalysts with excellent catalytic performance by incorporating Lewis acid sites onto carbon materials.

Highly efficient isomerization of glucose to fructose over Sn-doped silica nanotube

Isomerization of glucose to fructose is a fundamental and key intermediate process commonly included in the production of valuable chemicals from carbohydrates in biorefinery. Enhancement of fructose yield is a challenge. In this work, Sn-doped silica nanotube (Sn-SNT) was developed as a highly efficient Lewis acid catalyst for the selective isomerization of glucose to fructose. Over Sn-SNT, 69.1 % fructose yield with 78.5 % selectivity was obtained after reaction at 110 °C for 6 h. The sole presence of a large amount of Lewis acid sites in Sn-SNT without Brønsted acid site is one of the reasons for the high fructose yield and selectivity. Otherwise, high density of Si−OH groups in Sn-SNT can ensure the presence of Si−OH groups near the Sn sites, which is important for the isomerization of glucose to fructose, leading to the high fructose yield and selectivity. Furthermore, the Sn-SNT is recyclable.

Isomorphous incorporation of tin ions into extra-large pore framework with high-stannum content as efficient Lewis acid catalyst

Germanium-rich *CTH zeolite without organic molecules located inside pore channels experienced only partial structural collapse and subsequently repaired to high-silica structure analogous to the original topology in a short time. The surprise acid-hydrolysis process has caused a large amount of framework Ge ions were removed, giving rise to abundant hydroxyl nests. Benefiting from the unexpected variation of framework structure and chemical composition, stannosilicates Sn-*CTH with extra-large pores and various Sn loadings (Si/Sn molar ratio in the range of 30-∞) were post-prepared depending on the reaction between the added (NH4)2SnCl6 species and the formed silanol groups in the hydroxyl nests. The resultant Sn-*CTH zeolites were able to release significantly the diffusion limitations encountered by the bulky substrates and oxidants, exhibiting promising activities to catalyze the Baeyer-Villiger (B-V) oxidation of ketones with single oxidant either hydrogen peroxide (H2O2) or large-sized tert-butyl hydroperoxide (TBHP). Especially, high ε-caprolactone product selectivity was also obtained in the B-V oxidation of cyclohexanone using H2O2 oxidant through reducing the H2O2/cyclohexanone molar ratio as well as controlling appropriate reaction time, which was more efficient than the traditional Sn-Beta-F catalyst.

Regioselective Synthesis and Molecular Docking Studies of 1,5-Disubstituted 1,2,3-Triazole Derivatives of Pyrimidine Nucleobases

1,2,3-triazoles are versatile building blocks with growing interest in medicinal chemistry. For this reason, organic chemistry focuses on the development of new synthetic pathways to obtain 1,2,3-triazole derivatives, especially with pyridine moieties. In this work, a novel series of 1,5-disubstituted-1,2,3-triazoles functionalized with pyrimidine nucleobases were prepared via 1,3-dipolar cycloaddition reaction in a regioselective manner for the first time. The N1-propargyl nucleobases, used as an alkyne intermediate, were obtained in high yields (87-92%) with a new two-step procedure that selectively led to the monoalkylated compounds. Then, FeCl3 was employed as an efficient Lewis acid catalyst for 1,3-dipolar cycloaddition between different aryl and benzyl azides and the N1-propargyl nucleobases previously synthesized. This new protocol allows the synthesis of a series of new 1,2,3-triazole derivatives with good to excellent yields (82-92%). The ADME (Absorption, Distribution, Metabolism, and Excretion) analysis showed good pharmacokinetic properties and no violations of Lipinsky's rules, suggesting an appropriate drug likeness for these new compounds. Molecular docking simulations, conducted on different targets, revealed that two of these new hybrids could be potential ligands for viral and bacterial protein receptors such as human norovirus capsid protein, SARS-CoV-2 NSP13 helicase, and metallo-β-lactamase.

Highly Active La(III)-Based Metal-Organic Framework as a Heterogeneous Lewis Acid Catalyst for Friedel-Crafts Alkylation.

In this study, a novel La(III)-based two-dimensional (2D) metal-organic framework, [La2/3 (qptca)1/2 ] (referred to as SLX-2), from LaCl3 and 1,1' : 4',1'' : 4'',1''' : 4''',1''''-quinquephenyl]-2,2'',2'''',5''-tetracarboxylic acid (H4 qptca) was synthesized by conventional solvothermal method and thoroughly characterized by using X-ray single-crystal diffraction, powder X-ray diffraction, and thermogravimetric analyses. The 2D SLX-2 features a unique lanthanum center exposed to the skeleton and was used as an efficient Lewis acid catalyst for the Friedel-Crafts alkylation of indole and pyrrole with β-nitrostyrene along with a wide substrate scope, giving the desired products in good-to-high yields under the optimal reaction conditions. Furthermore, the catalyst was used for twenty cycles, with nearly no effect on its activity, and the reaction was heterogeneous in nature. Moreover, compared to the previous hydrogen-bond-donating MOF catalysts for such alkylation reactions, SLX-2 showed an excellent stability toward harsh acidic and basic environment, and gave comparable catalytic activities.

Synthesis of Cage-Shaped Borates Bearing Pyrenylmethyl Groups: Efficient Lewis Acid Catalyst for Photoactivated Glycosylations Driven by Intramolecular Excimer Formation.

We describe the synthesis and characterization of a photoactivated boron-based Lewis acid catalyst based on a cage-shaped triphenolic ligand with three pyrenylmethyl moieties. The obtained cage-shaped borate functioned as a photoactivated Lewis acid catalyst thanks to the flexible three pyrenylmethyl moieties. The deformation of the cage-shaped scaffold driven by intramolecular excimer formations of the pyrenes is a critical factor in realizing the photoactivation. Mannich-type reactions and glycosylations significantly were accelerated under 370 nm light irradiations. It is noteworthy that various glycosyl fluorides, which are not easily activated in photocatalytic systems due to their high C-F bond stability, are activated by the photoimproved catalytic activity of the catalyst.

Iron(III)‐Catalyzed Difluoroalkylation of Aryl Alkynes with Difluoroenol Silyl Ether in the Presence of Trimethylsilyl Chloride

AbstractThe reaction of non‐fluorinated silyl enol ether with alkyne is useful for the synthesis of β,γ‐unsaturated carbonyl compounds. However, most of the existing methods for realizing such organic transformation usually employ stoichiometric amounts of relatively expensive Lewis acids/metallic salts. Herein, an iron(III)‐catalyzed difluoroalkylation of aryl alkynes with difluoroenol silyl ether was developed. The reactions proceeded smoothly in the presence of a catalytic amount of iron(III) chloride, stoichiometric amounts of trimethylsilyl chloride, and 4 Å molecular sieves in dichloroethane (DCE) to afford the corresponding α‐alkenyl‐α,α‐difluoroketones in modest to good yields. Remarkably, among the various metallic salts screened, cheap and less‐toxic iron(III) salt was found to be the most efficient Lewis acid catalyst for the present reaction. In addition, in the absence of iron(III) chloride or trimethylsilyl chloride, either no reaction occurred or considerably reduced reaction performance was observed. Moreover, the use of Brønsted acid to replace iron(III) chloride as reaction catalyst failed to promote the reaction. The reaction could be scaled up and the obtained difluoroalkylated carbonyl compound serves as a versatile building block which could be subjected to late‐stage diversification to be converted into useful organic molecules containing CF2H and CF2CF2 moieties. Deuterated experiments showed that the proton in the generated alkene product should originate from trace amounts of water present in the reaction system.magnified image

Under-coordinated AlF3 clusters confined in carbon matrix with robust sintering resistance for dehydrofluorination of hydrofluorocarbons

The development of catalysts for the resource utilization of potent greenhouse gases, hydrofluorocarbons (HFCs) by catalytic pyrolysis is of great significance to alleviate the greenhouse effect. Fabricating small catalyst particles with high specific surface area leading to more Lewis acid sites is the effective strategies to achieve highly functional catalysts. However, catalysts tend to sinter at elevated temperatures. Herein, we synthesized carbon matrix confined Al2O3 clusters via the calcination of MIL-53-Al under N2 atmosphere. Then the Al2O3 clusters were in situ fluorinated and turned into AlF3 clusters accordingly. The derived carbon confined AlF3 clusters exhibited outstanding sintering resistance even following thermal treatment at 600 °C. Moreover, the carbon confined AlF3 clusters presented superior catalytic performance for 1,1-difluoroethane (HFC-152a) conversion with near 40% higher than that of AlF3 prepared by traditional precipitation. The excellent catalytic activity and stability were mainly ascribed to the abundant under-coordinated Al species with strong interaction with carbon matrix and high specific surface area. Thus, in this paper, we developed new practicable method to synthesize highly efficient Lewis acid catalysts with strong sintering resistance and abundant acid sites.

Cu(ii)-thiophene-2,5-bis(amino-alcohol) mediated asymmetric Aldol reaction and Domino Knoevenagel Michael cyclization: a new highly efficient Lewis acid catalyst.

The highly efficient Lewis acid-catalytic system Cu(ii)-thiophene-2,5-bis(amino-alcohol) has been developed for enantioselective Aldol reaction of isatin derivatives with ketones. The new catalytic system also proved to be highly enantioselective for the one pot three-component Domino Knoevenagel Michael cyclization reaction of substituted isatin with malononitrile and ethylacetoacetate. The chiral ligand (2S,2′S)-2,2′-((thiophene-2,5-diylbis(methylene))bis(azanediyl))bis(3-phenylpropan-1-ol) (L1) in combination with Cu(OAc)2·H2O employed as a new Lewis acid catalyst, furnished 3-substituted-3-hydroxyindolin-2-ones derivatives (3a–s) in good to excellent yields (81–99%) with high enantioselectivities (up to 96% ee) and spiro[4H-pyran-3,3-oxindole] derivatives (6a–l) in excellent yields (89–99%) with high ee (up to 95%). These aldol products and spiro-oxindoles constitute a core structural motif in a large number of pharmaceutically active molecules and natural products.

Molybdenum-modified mesoporous SiO2 as an efficient Lewis acid catalyst for the acetylation of alcohols.

A suitable, expeditious and well-organized approach for the acetylation of alcohols with acetic anhydride in the presence of 5%MoO3–SiO2 as an optimum environmentally benign heterogeneous catalyst was developed. The high surface area obtained for 5%MoO3–SiO2, 101 m2 g−1 compared to other catalysts, 22, 23, and 44 m2 g−1 for 5%WO3–ZrO2, 5%WO3–SiO2, and 5%MoO3–ZrO2, respectively, appears to be the driving force for better catalytic activity. Amongst the two dopants used, molybdenum oxide is the better dopant compared to its tungsten oxide counterpart. High yields of up to 86% were obtained with MoO3 doping while WO3 containing catalysts did not show any activity. Other reaction parameters such as reactor stirring speed, and solvent variation were studied and revealed that the optimum stirring speed is 400 rpm and cyclohexane is the best solvent. Thus, the utilization of affordable and nontoxic materials, short reaction times, reusability, and producibility of excellent yields of the desired products are the advantages of this procedure.

Boosting CO2 Conversion with Terminal Alkynes by Molecular Architecture of Graphene Oxide-Supported Ag Nanoparticles

Summary Carboxylation of terminal alkynes with CO2 via direct C–H bond activation is a highly appealing way to capture and convert CO2 but faces great challenges and difficulty. Here, we report an efficient catalyst that is prepared simply through introduction of p-tert-butylaniline into graphite oxide powders followed by localized growth of Ag nanoparticles (NPs). The bulky nature of p-tert-butylaniline facilitates the powder exfoliation, giving rise to mass production of uniform modified graphene oxide (tert-GO) nanosheets of 4 nm in thickness. Notably, Ag/tert-GO shows excellent catalytic activity for converting alkynes regardless of containing electron-donating or electron-withdrawing groups under mild reaction conditions. The synergy of the amide linkages on tert-GO nanosheets and the supported small-sized Ag NPs is recognized as the vital role in promoting adsorption of CO2 and subsequent conversion.

AlCl3 immobilized on silicic acid as efficient Lewis acid catalyst for highly selective preparation of dicyclohexylamine from the vapor phase hydroamination of cyclohexene with cyclohexylamine

An efficient and stable Lewis acid catalyst silicic acid (SA)-immobilized AlCl3 (AlCl3-SA) has been successfully prepared by the chemical bonding method in this work. The results indicated that the immobilized 15%AlCl3-SA exhibited excellent catalytic performance and stability in the vapor phase hydroamination of cyclohexene with cyclohexylamine. 58.5% cyclohexene conversion with 98.7% selectivity to dicyclohexylamine was still maintained after running for over 150 h, and the space time yield of dicyclohexylamine was 142.6 mol/h·m3. The developed AlCl3-SA catalyst had the advantages of low cost and long-time stable activity. Maybe this work provides a promising approach for hydroamination of olefins to amines.

12-Tungstoboric acid (H5BW12O40) as an efficient Lewis acid catalyst for the synthesis of chromenopyrimidine-2,5-diones and thioxochromenopyrimidin-5-ones: Joint experimental and computational study

H5BW12O40 (BWA), Keggin-type heteropoly acid was employed as an effective, eco-friendly and reusable Lewis acid catalyst for the high yielding synthesis of chromenopyrimidine-2,5-diones and thioxochromenopyrimidin-5-ones via multicomponent reaction (MCR) of differently substituted benzaldehydes, urea/thiourea, and 4-hydroxycoumarin in refluxing water. The BWA catalyst could be recovered by a simple filtration and applied in three successive runs with no noticeable decrease in the yield. Interestingly, this catalyst structure pattern may act as useful model for the design and assembly of the functional molecule-based catalysts, especially in the field of molecular sieve materials. Moreover, thermochemical properties in the synthesis of title compounds were assessed using density functional theory (DFT) calculations.

Synthesis of Cage-Shaped Aluminum Aryloxides: Efficient Lewis Acid Catalyst for Stereoselective Glycosylation Driven by Flexible Shift of Four- to Five-Coordination.

Monomeric cage-shaped aluminum aryl oxides 1Al were synthesized using tripodal triphenolic ligands. The Lewis acidity and catalytic activity of the obtained 1Al·py were investigated. The Lewis acidity of 1Al·py originates from the flexible change in the coordination number of the aluminum center, allowing the catalytic O-glycosylation to occur with a high efficiency and an unusual stereoselectivity.

Titanium tetrachloride incorporated crosslinked polystyrene copolymer as an efficient and recyclable polymeric Lewis acid catalyst for the synthesis of Β-amino carbonyl compounds at room temperature

An efficient and eco-friendly procedure for one-pot synthesis of β-amino carbonyl compounds by three-component reaction of aromatic aldehydes, acetophenone, and aromatic amines via a Mannich type reaction using a stable tightly bound complex, titanium tetrachloride incorporated crosslinked polystyrene copolymer (PS/TiCl4), as a water tolerant, recoverable, and reusable polymeric Lewis acid catalyst in ethanol at room temperature is reported. The complex of the polystyrene and TiCl4 provides a shelf-stable acidic, water tolerant material, and it is not easily hydrolyzed by water. Our findings thus show a novel and improved modification of the Mannich type reaction in terms of mild reaction conditions, clean reaction profiles, applicability to various substrates using a simple workup procedure which makes this reaction an interesting alternative to previously applied procedures. The recyclability of the catalyst makes this protocol environmentally benign.

The synthesis of hierarchical Sn-Beta zeolite via aerosol-assisted hydrothermal method combined with a mild base treatment

Abstract The Sn-Beta zeolite is an efficient Lewis acid catalyst for a wide range of chemical reactions. Here a seed-free aerosol-assisted hydrothermal strategy is used to synthesize plate-like Sn-Beta zeolite with higher tin content. A majority of Sn species were transformed into the framework of Beta zeolite as the desired tetrahedral coordination state, which creates strong Lewis acid sites. Moreover, the diffusion property of the Sn-Beta zeolite can be further improved by a mild base-surfactant (NH3˙H2O-CTAB) treatment. The addition of CTAB can not only narrow the mesopore distribution but also prevent the excessive loss of Sn species. The obtained hierarchical Sn-Beta zeolite exhibits an enhanced catalytic performance in the Baeyer–Villiger oxidation of bulky ketone.

First Report on 3‐(3‐oxoaryl) Indole Derivatives as Anticancer Agents: Microwave Assisted Synthesis, In Vitro Screening and Molecular Docking Studies

AbstractIn this study ZrCl4 was identified as an efficient Lewis acid catalyst for the synthesis of 3‐(3‐oxoaryl) indole derivatives via microwave assisted Michael addition of 2‐phenylindole with chalcones under solvent‐free condition. The reaction proceeds smoothly with high efficiency under green reaction condition to afford a range of 3‐(3‐oxoaryl) indole derivatives exclusively within a short period of time in excellent yields. The synthesized compounds have shown promising in vitro anticancer activity against murine melanoma (B16F10) and human breast cancer (MCF7) cell lines. Molecular docking analysis showed that this type of indole derivatives may act as anticancer agents through the inhibition of tubulin polymerization.

Zn(L‐proline)2 as an efficient and reusable catalyst for the multi‐component synthesis of pyran‐annulated heterocyclic compounds

We have developed a simple, straightforward and highly efficient multi‐component one‐pot synthesis of 2‐amino‐3‐cyano‐4H‐pyrans and pyran‐annulated heterocyclic compounds. Zn(L‐proline)2 has been utilized as a mild and efficient Lewis acid catalyst for the three‐component reaction of aromatic aldehydes, malononitrile and enolizable C‐H acids or activated phenols to synthesize pyran‐annulated scaffolds. 3‐Methyl‐1‐phenyl‐2‐pyrazolin‐5‐one, 4‐hydroxycoumarine, dimedone, 4‐hydroxy‐6‐methyl‐2‐pyrone, resorcinol, 1‐naphthol and 2‐naphthol were used as activated C‐H acids. The products were isolated in high yields via vacuum filtration and without using any chromatography. The Zn(L‐proline)2 was recovered and reused in another reaction (three times) without significant loss of activity.

A simple, direct synthesis of 3-vinylindoles from the carbocation-catalysed dehydrative cross-coupling of ketones and indoles. A combined experimental and computational study

A straightforward synthesis of a library of largely new 3-vinylindoles via a clean dehydrative coupling reaction between ketones and indoles has been developed. Highly stable, non-nucleophilic aryl(2-methylindol-3-yl)methylium salts have been used as efficient Lewis acid catalysts. The advantages of the reaction are the use of equimolar amounts of inexpensive and easily available reagents, the low catalyst amount, high atom efficiency, the production of only one molecule of water as a by-product and the mild reaction conditions. Computational studies of two specific reaction mechanism instances show that both steric and electronic effects heavily influence the nature of the final products, whether a methyl group in position 2 of the indole is present or absent.