Oxidative Cyclization Research Articles

Cu‐Catalyzed Oxidative Tandem Coupling and Cyclization of 2‐Aminonaphthalenes to Synthesize Dibenzo[c, g]carbazoles

AbstractA Cu(II) complex with a bipyridyl ligand bearing a Brønsted acid was used to catalyze the tandem oxidative coupling and cyclization of 2‐aminonaphthalenes to give N‐substituted‐dibenzo[c,g]carbazoles. The incorporation of an appended acidic moiety to the ligand was found to be key to the selective formation of dibenzocarbazoles over 2,2’‐diamino‐1,1’‐binaphthalene (BINAM), which is known as an irreversible byproduct. This highly efficient method yields a wide array of dibenzo[c,g]carbazoles featuring diverse functional groups as well as electronic properties. The selected dibenzo[c,g]carbazoles exhibited high photoluminescence quantum yields of up to 100 % and are promising chromophores for advanced materials.

Theoretical Study on Pt1/CeO2 Single Atom Catalysts for CO Oxidation

Understanding the influence of structural configurations on catalytic performance is crucial for optimizing atom‐efficient single‐atom catalysts (SACs). In this study, we conducted a density functional theory (DFT) investigation of single Pt atoms positioned at step‐edges and within a solid solution on the CeO2(111) surface. We compared these configurations in terms of thermodynamic stability, electronic properties, and further potential energy surfaces for CO oxidation. Stability studies revealed that the solid solution catalyst exhibits greater stability compared to the step‐edge catalyst. Additionally, the Pt in the solid solution catalyst can effectively activate lattice oxygen atoms, making the catalyst more conducive to the formation of oxygen vacancies. The CO oxidation process was analyzed using the Mars‐van Krevelen mechanism, revealing that the solid solution catalyst possesses a more moderate CO adsorption energy. This, coupled with its lower oxygen vacancy formation energy, leads to reduced energy barriers throughout the CO oxidation cycle. Our findings highlight the strong dependence of catalytic activity on the specific configuration of Pt atoms within the CeO2 matrix, with the solid solution model demonstrating superior catalytic efficiency compared to the step‐edge‐supported Pt catalysts.

Synthesis of 3‐Acyl‐1‐Indenones by Oxidative Cyclization of Symmetrical and Unsymmetrical Aryldiynes Using Palladium Nanoparticles (Pd‐BNP) as Reusable Nano Catalyst

AbstractAn efficient, stable and reusable binaphthyl stabilized palladium nanoparticles (Pd‐BNP) catalyzed synthesis of 3‐acyl‐1‐indenone derivatives from oxidative cyclization of symmetrical and unsymmetrical aryldiynes using DMSO as a solvent as well as an oxidant has been established. The scope of the reaction has been studied with various aryldiynes having electron‐donating and electron‐withdrawing groups that afforded good yields. Pd‐BNP catalyst can be recovered and reused for up to four cycles without major changes in particle size and reactivity.

Modifications of Prenyl Side Chains in Natural Product Biosynthesis

AbstractIn recent years, there has been a growing interest in understanding the enzymatic machinery responsible for the modifications of prenyl side chains and elucidating their roles in natural product biosynthesis. This interest stems from the pivotal role such modifications play in shaping the structural and functional diversity of natural products, as well as from their potential applications to synthetic biology and drug discovery. In addition to contributing to the diversity and complexity of natural products, unique modifications of prenyl side chains are represented by several novel biosynthetic mechanisms. Representative unique examples of epoxidation, dehydrogenation, oxidation of methyl groups to carboxyl groups, unusual C−C bond cleavage and oxidative cyclization are summarized and discussed. By revealing the intriguing chemistry and enzymology behind these transformations, this comprehensive and comparative review will guide future efforts in the discovery, characterization and application of modifications of prenyl side chains in natural product biosynthesis.

Manganese- Mediated Cascade Radical Oxidative Cyclization/1,6-Conjugate Addition of Unsaturated Oximes with p-Quinone methides: Facile Access to β,β-Diarylmethine Isoxazolines.

A simple and efficient strategy for the synthesis of structurally diverse β,β-diarylmethine substituted isoxazoline derivatives have been developed. This approach employs a manganese-promoted oxidative cyclization coupled with a 1,6-conjugate addition of unsaturated oximes to p-quinone methides. The key features of this study include the formation of C-O and C-C bonds through intramolecular and intermolecular interactions, facilitated by in situ generated iminoxyl radicals. β,β-diarylmethine substituted isoxazolines, bearing a wide range of functional groups, were isolated in high yields.

Enhanced H2S removal efficiency using CuO/Al2O3 catalyst impregnated with Ca(NO3)2: Influence of calcination temperature and mechanistic insights

A series of Ca(NO3)2-CuxO/Al2O3 catalysts with different calcination temperatures were designed to remove H2S effectively. Experimental and characterization results indicate that the calcination temperature can influence the catalyst's specific surface area, basic sites, and oxygen vacancies (VOs) concentration, thereby promoting its desulfurization performance. The Ca(NO3)2-CuxO/Al2O3 catalyst, calcined at 230 °C, exhibits an optimal surface structure. It demonstrates optimal H2S desulfurization performance at a temperature of 60 °C and relative humidity of 60 %, achieving a removal capacity of 486.67 mg/g. The VOs in CuxO (CuO and Cu2O) induce a unique catalytic of H2O, which generates hydroxy radicals (·OH) to oxidize the H2S anion to S. The introduction of Ca2+ provides basic sites to buffer pH, and NO3- with H+ removes H2S through cyclic oxidation, significantly enhancing the desulfurization performance of the Cu-based catalyst. The CaO-CuxO/Al2O3 catalyst, calcined at 700 °C, suffers from a deteriorated catalyst structure, leading to the rapid formation of desulfurization by-products due to the presence of CaO covering the catalyst surface. This diminishes the effectiveness of Cu, significantly impairing the catalyst's desulfurization performance (150.47 mg/g). Consequently, desulfurization mechanisms of Ca(NO3)2-CuxO/Al2O3 and CaO-CuxO/Al2O3 are proposed, offering effective strategies for the design and optimization of subsequent high-efficiency catalysts.

Catalytic Cycloisomerization-Oxidative Cyclization Reaction Sequence of Enyne Diesters Derived from 2-Propargyloxyarylaldehydes.

Enyne diesters derived from 2-propargyloxyarylaldehydes are converted into 2-oxopyranochromenes via In(OTf)3-catalyzed cycloisomerization and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-mediated oxidative cyclization reaction sequence in one pot. The process possesses broad substrate scope and good functional group compatibility and generates various 4-(hetero)aryl-substituted 2-oxopyranochromenes in 32-79% yields (over two steps). 2-Oxopyranochromenes undergo selective decarboxylation under Krapcho conditions. When treated with aliphatic secondary amines in DMF, 2-oxopyranochromenes undergo decarboxylative amination at ambient temperature to generate 2-amino-substituted functionalized chromenes in good yields.

Studies on hardness, elastic modulus and high temperature oxidation resistance of TiC and TiB2 dispersed titanium aluminide (Ti45Al5Nb0.5Si) composites developed by laser direct energy deposition

In this study, TiC (5 to 10wt.%) and TiB2 (5 to 10wt.%) reinforced TiAl (Ti45Al5Nb0.5Si) composites have been developed by laser direct energy deposition (LDED) process. The microstructures of TiAl/TiC and TiAl/TiB2 composites consist of TiC and TiB2 particles dispersed in γ and α2 matrix. The microhardness of the composites is improved from 571 HV to 634-683 HV (for TiC dispersion) and 649-694 HV (for TiB2 dispersion). The activation energy of cyclic oxidation is increased from 228kJ/mol (Ti45Al5Nb0.5Si) to 271-301kJ/mol (TiC dispersion) and 262-296kJ/mol (TiB2 additions). The mechanism of oxidation of the composites is established.

Utilization of waste citrus limetta peel for the green synthesis of iron catalyst and its subsequent application in fluidized-bed Fenton-like process for environmental sustainable treatment of organic pollutant

This work focuses on the environmental friendly synthesis of an iron-based catalyst utilizing extract from waste citrus limetta peels. The main objective is to encourage the sustainable use of bio-waste materials in catalytic processes. This innovative method demonstrates the efficacy of bio-derived materials in catalysis by removing the need for hazardous chemicals. The green-synthesized catalyst was analyzed using many characterization methods, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). These analyzed results give insightful information on the physicochemical properties of green-synthesized catalysts. Furthermore, the prepared catalyst was utilized in a fluidized-bed reactor to facilitate the Fenton degradation of dye effluent, with a specific focus on the commonly used Eosin yellow (EY) dye. The iron catalyst derived from plant-based waste material accomplished an impressive 98% degradation of EY within a 90-minute time frame under optimized working conditions, using a minimal quantity of catalyst. An in-depth analysis was conducted to study the kinetics and process mass transfer in order to improve the comprehension of catalytic processes occurring in the fluidized-bed reactor. The Fenton decomposition of dye effluent is likely to be explained by first-order reaction kinetics. Additionally, confirmed enhanced catalytic durability and decreased deactivation of surface sites of the prepared catalyst after three consecutive oxidation cycles. These findings underscore the potential of this approach in sustainable wastewater treatment, highlighting both its efficiency and cost-effectiveness.

High‐Temperature Oxidation Response of 444 Ferritic Stainless Steel in a Synthetic Automotive Exhaust Gas

The high‐temperature oxidation behavior of 444 ferritic stainless steel has been studied in cyclic oxidation experiments using synthetic automotive exhaust gas atmospheres at 950 and 1050 °C. The weight gain per unit area of the 444 ferritic stainless steel following oxidation at 950 °C for 100 h iss 85.7% lower than recorded at 1050 °C. The oxide scale at both temperatures consisted of Fe–Cr and Mn–Cr spinels in the outer layer and Cr2O3 in the inner layer. Nodule formation and spallation of the oxide scale are identified as the main causes of breakaway oxidation. The depth of the internal oxides gradually increases with the oxidation time. The nucleation and growth of internal SiO2 result in the formation of metal protrusions, which are eventually consumed in the formation of a SiO2 layer. The SiO2 layer is formed at the interface between the oxide scale and the substrate at 1050 °C. The nucleation and growth of internal SiO2, in combination with lateral growth of SiO2 at the Cr2O3 layer/substrate interface contributed to the formation of the SiO2 layer.

Synthesis of Double Benzimidazole‐Fused Quinazolines and Pyrimidines Catalyzed by Recyclable Magnetic Cu‐MOF‐74

Abstract2‐(2‐Bromoaryl)‐ and 2‐(2‐bromovinyl)benzimidazoles are combined and cyclized with benzimidazoles using a catalytic amount of magnetic Cu‐MOF‐74 (Fe3O4@SiO2@Cu‐MOF‐74) and a base under O2 atmosphere, yielding the corresponding double benzimidazole‐fused quinazolines and pyrimidines. The catalyst can be recovered using a magnetic bar and reused multiple times without significant loss of catalytic activity. The reaction mechanism likely involves the initial formation of a C−N coupled intermediate through nucleophilic aromatic substitution, followed by oxidative cyclization.

Exploring complete catalytic cycle of methane oxidation to methanol on Cu2O2 stabilized within MIL-53(Al) framework: A combined DFT and microkinetic study

Although inspiration from copper-based natural enzymes has shown promise in improving catalyst design for methane-to-methanol (MTM) oxidation, high productivity, and selectivity under mild conditions remain a significant challenge. This study constructs the dinuclear copper (Cu2) species stabilized within the metal-organic framework (MOF), MIL-53(Al), containing Cu as efficient catalytic sites and explores the ability of different oxidants (O2, N2O, and H2O2) to oxidize Cu2 into the dicopper-oxo (Cu2O2) species using density functional theory (DFT) calculations. Our results indicate the kinetic and thermodynamic favorability of Cu2O2 species formation using O2 as an oxidant within the MIL-53(Al) framework. Furthermore, the thermal stability of Cu2O2/MIL-53(Al) has been verified via ab initio molecular dynamics (AIMD) calculations. The kinetics of the complete MTM oxidation cycle over Cu2O2/MIL-53(Al) have been studied using both DFT and microkinetic simulation methods. The present study predicts that the C-H activation on the Cu2O2/MIL-53(Al) has a low free energy barrier (0.77 eV) and that the high stability of CH3 and its very low free energy barrier in the C-O coupling step favors the methanol formation over the formaldehyde. More importantly, Cu2O2/MIL-53(Al) exhibits high methanol selectivity owing to the inhibition of CH3 dehydrogenation and low methanol desorption energy (0.21 eV). Microkinetic simulations confirm the methanol production under relatively mild reaction conditions (200–280 K and 1 bar). This work provides insights into the feasibility of selective MTM oxidation over this family of MOF under mild conditions.

Influence of NiCrAlY coating on anti-corrosion of M951 alloy

M951 alloy is a cast nickel-based super-alloy widely used in gas turbines and aircraft engines, thus a suitable high temperature protective coating must be applied on its surface to enhance the corrosion resistance. In this research, NiCrAlY coating was deposited on M951 by arc ion plating. TGA at 1100 °C, cyclic oxidation at 1000 °C and hot corrosion in molten Na2SO4+25 wt% K2SO4 salt at 850 °C of M951 bare alloy and NiCrAlY coating specimens were investigated respectively. After TGA and cyclic oxidation, mixed oxides of NiO, NiAl2O4, Nb2O5 and Al2O3 formed on M951 surface, which spalled seriously during cyclic oxidation process. Thin, continuous and adhesive α- Al2O3 formed on the surface of NiCrAlY coating after both oxidation process. In molten Na2SO4+25 wt%K2SO4 salt at 850 °C, catastrophic corrosion occurred for the M951 alloy only after 10 hours, while thin and continuous θ- Al2O3 film formed on the surface of the NiCrAlY coating. In a word, NiCrAlY coating greatly improved the high temperature oxidation and hot corrosion resistance of the M951 superalloy. This study will further refine the oxidation and corrosion behaviors of M951 superalloy under different high temperature protective coatings and provides theoretical and experimental basis for the application of M951 superalloy in corrosive environments.

Bridging to Commercialization: Record-Breaking of Ultra-Large and Superior Cyclic Stability Tungsten Oxide Electrochromic Smart Window.

Electrochromic smart windows (ESWs) can significantly reduce energy consumption in buildings, but their cost-effective, large-scale production remains a challenge. In this study, the instability of black phosphorus is leveraged to induce the growth of the tungsten oxide film through its decomposition process, inspired by the 2D material-assisted in situ growth (TAIG) method. This approach results in the preparation of large-scale, high-performance WO3-x·nH2O (n<2) films. Characterization techniques and DFT calculations confirm efficient regulation ofstructural water and oxygen vacancies during TAIG preparation. The WO3-x·nH2O films exhibit excellent electrochromic (EC) properties, including high transmittance modulation (74.2%@1100nm), fast switching time (tc=5.5s, tb=3.8s), high coloration efficiency (124.7cm2C-1), and superior cyclic stability (transmittance modulation retained 94.7% after 20000 cycles). Ultra-largeWO3-x·nH2O film are prepared via a simple immersion process, and fabricated into a large-area ESW under facile laboratory conditions, demonstrating the economic and practical feasibility of this approach in industrial-scale production. Operated by the intelligent control circuit, the ESWexhibits remarkable EC properties and cyclic stability This research represents a milestone in improving the performance and industrial-scale production of ESWs, bridging the gap to the commercialization of EC technology.

Gold nanoparticle-decorated amorphous carbon for oxidative cyclization of anthranilamide and aryl alcohols.

Herein, gold nanoparticle-decorated amorphous carbon (Au/AC) was prepared by reducing chloroauric acid and layering it on amorphous carbon. The characteristics of Au/AC were examined using FT-IR, XRD, TGA, SEM, EDS, and XPS. To assess its catalytic activity, Au/AC was tested in a reaction involving anthranilamide and benzyl alcohol at 110 °C for 24 hours. This reaction yielded various 2-phenylquinazolin-4(3H)-one derivatives in moderate to good yields (44-80%). Furthermore, control experiments were conducted to demonstrate the oxidation and cyclization functions of Au/AC. Noteworthy aspects of this approach included the ease of isolating Au/AC (via recrystallization) and the ability to recycle it.

Ag(I)-Catalyzed Oxidative Cyclization of 1,4-Diynamide-3-ols with N-Oxide for Divergent Synthesis of 2-Substituted Furan-4-carboxamide Derivatives.

This work reports Ag(I)-catalyzed oxidative cyclizations of 1,4-diynamide-3-ols with 8-methylquinoline oxide to form 2-substituted furan-4-carboxamides. The reaction chemoselectivity is distinct from that reported in previous work by Hashmi. We performed density functional theory calculations to elucidate our proposed mechanism after evaluation of the energy profiles of two possible pathways. In this Ag(I) catalysis, the calculations suggest that the amide and alkyne groups of the 3,3-dicarbonyl-2-alkyne intermediates tend to chelate with the Ag(I) catalyst, further inducing a formyl attack at the Ag(I)-π-alkyne moiety to deliver the observed products.

A novel copper(II) complex with a salicylidene carbohydrazide ligand that promotes oxidative stress and apoptosis in triple negative breast cancer cells.

We report the synthesis, characterization, anti-cancer activity and mechanism of action of a novel water-soluble Cu(II) complex with salicylidene carbohydrazide as the ligand and o-phenanthroline as the co-ligand. The synthesized complex (1) was characterized by FT-IR, EPR, and electronic spectroscopy, as well as single crystal X-ray diffraction. This compound was found to be paramagnetic from EPR spectra and X-ray crystallography revealed that the molecule crystallized in an orthorhombic crystal system. The crystal lattice was asymmetric containing two distinct binuclear copper complexes containing the Schiff base as the major ligand, o-phenanthroline as a co-ligand, two nitrate anions, and two water molecules. The Cu(II) in the first site coordinated with the enolised ligand comprising enolate O-, phenolate O-, and the imine N and N,N from o-phen. The major part of this complex exists as Cu(II) coordinated with two H2O molecules at the second site with nitrate acting as the counter anion. However, a smaller portion of the complex exists where Cu(II) is coordinated with NO3- and H2O, and the remaining water molecule acts as lattice water. It was tested for DNA binding and cleavage properties which revealed that it binds in an intercalative mode to CT-DNA with Kb value of 1.25 × 104 M-1. Furthermore, cleavage studies reveal that the complex has potential for efficient DNA cleavage under both oxidative and hydrolytic conditions. It was able to enhance the rate of cleavage by 2.8 × 108 times. The complex shows good cytotoxicity to breast cancer monolayer (2D) as well as spheroid (3D) systems. The IC50 values for MDA-MB-231 and MCF-7 monolayer culture was calculated as 1.86 ± 0.17 μM and 2.22 ± 0.08 μM, respectively, and in (3D) spheroids of MDA-MB-231 cells, the IC50 value was calculated to be 1.51 ± 0.29 μM. It was observed that the complex outperformed cisplatin in both breast cancer cell lines. The cells treated with complex 1 underwent severe DNA damage, increased oxidative stress and cell cycle arrest which finally led to programmed cell death or apoptosis in triple negative breast cancer cells through an intrinsic pathway.

The influence of CeO2 on the oxidation resistance of TaC/Ni composites

The in-situ TaC/Ni composites with different CeO2 content (0 wt%, 1 wt%, 2 wt%) were prepared by reactive sintering method, and their oxidation behavior in air at 1073 K was analyzed by static cyclic oxidation method to investigate the influence mechanism of CeO2 on the oxidation resistance of composites. The results show that the CeO2 particles are distributed around the TaC particles in the Ni matrix, and the oxidation behavior of composites with different CeO2 content conforms to the linear kinetic law. The oxide film is mainly composed of NiTa2O6 and a small amount of NiO. The generation reactions of Ta2O5 and NiTa2O6 induce a high expansion and compressive stress in oxide scale, leading to the formation of nonprotective oxide film with pores and cracks on the surface. As the addition of CeO2 increases from 0 wt% to 2 wt%, the thickness of oxide scale on composites obviously reduces from 505 μm to 122 μm, and the Ni and Ta oxides content decreases, leading to the reduction of pores and cracks in oxide scale. The Ce ion generated from the dissolution of CeO2 particles mainly distributes in the Ta oxides during the oxidation process, which hinders the outward diffusion of Ni and Ta ions, resulted in the improved oxidation resistance of TaC/Ni composites.

Defect-Rich Regulatory Activity Strategy: Disordered Structure for Enhanced Catalytic Interfacial Reaction of Chlorobenzene.

In contrast to previous defect engineering methods, the preparation of amorphous materials can obtain abundant defect sites through a simple way, which is expected to effectively degrade Volatile Organic Compounds (VOCs) under milder conditions. However, in-depth and systematic studies in this area are still lacking. Novel types of amorphous CeMnx catalysts with abundant defects were prepared through simple hydrothermal synthesis and used for Cl-VOCs catalysis for the first time. Experimental characterizations and DFT calculations proved that Ce doping induced MnO2 lattice distortion, which led to the transformation of CeMnx into an amorphous structure and the formation of abundant defect sites. It was observed that CeMn0.16 was able to eliminate chlorobenzene (CB) at 200 °C, and the CO2 yields and the selectivity of inorganic chlorine was significantly higher than that of MnO2. The 18O isotope kinetic experiments revealed that the interfacial reaction process followed the MVK mechanism. The large number of oxygen vacancies accelerated the migration of lattice oxygen from the interior to the exterior, enhancing the ability to trap gas-phase oxygen. Mn4+ acted as the main active center to participate in CB catalysis, and the resulting reactive oxygen species (ROS) and Mn3+-[O2-]-Ce4+ further accelerated the entire oxidation cycle.

Exploring Topochemical Oxidation Reactions for Reversible Tuning of Thermal Conductivity in Perovskite Fe Oxides.

We present a study on the reversibility of thermal conductivity in iron oxides through topochemical oxygen exchange between brownmillerite (BM) (Ca,Sr)FeO2.5 and perovskite (PV) (Ca,Sr)FeO3.0. By using different oxidation methods, including gas phase (O2/O3), liquid phase (NaOCl in H2O), and solid electrolyte (Y2O3:ZrO2), we demonstrate that the oxidation pathway has a critical influence on the reversibility of the ionic-exchange process. Cyclic oxidation and reduction using O2/O3 or NaOCl lead to an important accumulation of structural defects, undermining the reversibility of thermal conductivity. In the case of wet oxidation, we demonstrate an inherent tendency of negative charge-transfer oxides toward amorphization and elucidate the origin of this effect. Conversely, the electrochemical injection of the O2- ions via a Y2O3:ZrO2 solid electrolyte reduces structural damage significantly, enhancing both reversibility and durability. This study underscores the importance of selecting appropriate topochemical oxygen exchange methods to maintain structural integrity and optimize functional performance in oxide-based tunable devices.