Recent Advancement of Ullmann Condensation Coupling Reaction in the Formation of Aryl-Oxygen (C-O) Bonding by Copper-Mediated Catalyst

Single-Atom Catalysts through Pressure-Controlled Metal Diffusion

Single-atom catalysts (SACs) open up new possibilities for advanced technologies. However, a major complication in preparing high-density single-atom sites is the aggregation of single atoms into clusters. This complication stems from the delicate balance between the diffusion and stabilization of metal atoms during pyrolysis. Here, we present pressure-controlled metal diffusion as a new concept for fabricating ultra-high-density SACs. Reducing the pressure inhibits aggregation substantially, resulting in almost three times higher single-atom loadings than those obtained at ambient pressure. Molecular dynamics and computational fluid dynamics simulations reveal the role of a metal hopping mechanism, maximizing the metal atom distribution through an increased probability of metal-ligand binding. The investigation of the active site density by electrocatalytic oxygen reduction validates the robustness of our approach. The first realization of Ullmann-type carbon-oxygen couplings catalyzed on single Cu sites demonstrates further options for efficient heterogeneous catalysis.

Ultrasound-assisted Cu(II) Strecker-functionalized organocatalyst for green azide-alkyne cycloaddition and Ullmann reactions

A new aminonitrile-functionalized Fe3O4 has been synthesized via the Strecker reaction, the designed aminonitrile ligand on the surface of the magnetic core coordinated to copper(II) to obtain the final new catalyst. The fabricated nanocatalyst was characterized by Fourier transform Infrared (FT-IR), Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), Transmission Electron Microscopy (TEM), Vibrating-Sample Magnetometer (VSM), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), and Thermogravimetric Analysis (TGA). The high tendency of nitrogens in the aminonitrile functional group to make a complex with Cu(II) has caused the practical activity of this nucleus in this catalyst. This nanocatalyst performance was investigated in azide-alkyne Huisgen cycloaddition (3 + 2) reaction for achieving to 1,4-disubstituted 1,2,3-triazoles in water as a green media at room temperature. In another try, Classic Ullmann Reaction was investigated for the synthesis of biaryls at 85 °C promoted by ultrasonic condition (37 kHz). The reaction scope was explored using different reactants and the results of using this developed catalytic system demonstrated its capacity to reduce the reaction time and enhance the reaction efficiency to provide good to excellent product yield. Conversely, the simple recycling and reusability of this catalyst for at least six times without any noticeable leaching of copper makes it a potential future catalyst for synthesizing such compounds.

Microwave-Assisted, Copper-Catalyzed Domino O-H/C-H Arylation Reaction toward the Synthesis of Oxygen-Doped Polyaromatic Molecules

Benzoxanthenes and their analogues are a very important class of compounds mainly due to their wide range of biological and technological applications. The development of a new methodology for their synthesis, involving an Ullmann-type coupling followed by an intramolecular C-H arylation, catalyzed by copper in a domino fashion, is reported. A variety of para-substituted phenols are amenable to this methodology, affording the desired products in moderate to good yields. Our protocol is expedient and practical and is carried out under microwave irradiation in only 3 min under air. A plausible catalytic cycle is proposed based on experimental mechanistic investigations and density functional theory (DFT) calculations.

Fe3O4 supported [Cu(ii)(met)(pro-H)2] complex as a novel nanomagnetic catalytic system for room temperature C-O coupling reactions

In this study, a newly-designed copper(ii) complex of metformin and l-proline which was immobilized on Fe₃O₄ MNPs was developed. The structure of the catalyst platform was fully characterized using spectroscopic analyses. Moreover, the catalytic activity of [Fe₃O₄@Cu(ii)(Met)(Pro-H)₂] was investigated in a one-pot synthesis of a variety of functionalized ethers in reasonable to excellent yields through Ullman reaction in an aqueous environment using various aryl halides, phenol, and Cs₂CO₃ and without using any external Cu-reducing agents. Notably, gentle catalytic conditions, quick reaction times, applicability, low cost, and preventing dangerous chemicals and solvents during synthesis and catalytic application are some of the superior properties of the [Fe₃O₄@Cu(ii)(Met)(Pro-H)₂] complex. Furthermore, the catalyst can be reused for several runs (at least eight times) without remarkable loss in efficiency.

Microwave-Assisted Cu-Catalyzed Diaryletherification for Facile Synthesis of Bioactive Prenylated Diresorcinols

Prenylated diresorcinols exhibit various bioactivities, including cytotoxic, antibacterial, and antifungal activities. Therefore, establishing facile and efficient synthetic routes for prenylated diresorcinols facilitates their development as chemical probes or drugs with a novel mode of action. In this study, microwave-assisted copper catalysis was explored as a cost-effective and environmentally friendly method for the cross-coupling of sterically hindered ortho-prenylated phenols and aryl halides to produce bioactive prenylated diresorcinols, diorcinol I and leotiomycene B. Notable advantages of microwave-assisted catalysis include not only operational simplicity and rapid heating but also shorter reaction times and higher chemical yields. In addition, highly regioselective prenylation of phenol was achieved for the preparation of ortho-prenyl phenol via directed lithiation and subsequent alkylation. This study provides valuable insights for the preparation of other bioactive prenylated diresorcinols. Furthermore, considering that prenylated benzenoids are biosynthetic precursors of various polycyclic natural products, this synthetic route could be expanded to more complex bioactive compounds possessing diaryl ethers.

Copper-Catalyzed Reactions of Aryl Halides with N-nucleophiles and Their Possible Application for Degradation of Halogenated Aromatic Contaminants

This review summarizes recent applications of copper or copper-based compounds as a nonprecious metal catalyst in N-nucleophiles-based dehalogenation (DH) reactions of halogenated aromatic compounds (Ar-Xs). Cu-catalyzed DH enables the production of corresponding nonhalogenated aromatic products (Ar-Nu), which are much more biodegradable and can be mineralized during aerobic wastewater treatment or which are principally further applicable. Based on available knowledge, the developed Cu-based DH methods enable the utilization of amines for effective cleavage of aryl-halogen bonds in organic solvents or even in an aqueous solution.

Organosulphur and organoselenium compounds as emerging building blocks for catalytic systems for O-arylation of phenols, a C-O coupling reaction

Diaryl ethers form an important class of organic compounds. The classic copper-mediated Ullmann diaryl ether synthesis has been known for many years and involves the coupling of phenols with aryl halides. However, the use of high reaction temperature, high catalyst loading and expensive ligands has created a need for the development of alternative catalytic systems. In the recent past, organosulphur and organoselenium compounds have been used as building blocks for developing homogeneous, heterogeneous and nanocatalysts for this C-O coupling reaction. Homogeneous catalytic systems include preformed complexes of metals with organosulphur and organoselenium ligands. The performance of such complexes is influenced dramatically by the nature of the chalcogen (S or Se) donor site of the ligand. Nanocatalytic systems (including Pd₁₇Se₁₅, Pd₁₆S₇ and Cu_1.8S) have been designed using a single-source precursor route. Heterogeneous catalytic systems contain either metal (Cu or Pd) or metal chalcogenides (Pd₁₇Se₁₅ or Cu_1.8S) as catalytically active species. This article aims to cover the simple and straightforward methodologies and approaches that are adopted for developing catalytically relevant organosulfur and organoselenium ligands, their homogeneous metal complexes, heterogeneous and nanocatalysts. The effects of chalcogen (S or Se) donor, halogen (Cl/Br/I) of aryl halide, nature (electron withdrawing or electron donating) of substituents present on the aromatic ring of aryl halides or substituted phenols and position (ortho or para) of substitution on the results of catalytic reactions have been critically analyzed and summarized. The effect of composition (Pd₁₇Se₁₅ or Pd₁₆S₇) on the performance of nanocatalytic systems is also highlighted. Substrate scope has also been discussed in all three types of catalysis. The superiority of heterogeneous catalytic systems (e.g., Pd₁₇Se₁₅ immobilised on graphene oxide) indicates the bright future possibilities for the development of efficient catalytic systems using similar or tailored ligands for this reaction.

Functionalization of graphene oxide with a hybrid P, N ligand for immobilizing and stabilizing economical and non-toxic nanosized CuO: an efficient, robust and reusable catalyst for the C–O coupling reaction in O-arylation of phenol

A new graphene oxide based heterogeneous catalytic system holding CuO nanoparticles through P and N donor sites for the C–O coupling reaction.

Copper nanocatalysts applied in coupling reactions: a mechanistic insight

Copper-based nanocatalysts have seen great interest for use in synthetic applications since the early 20th century, as evidenced by the exponential number of contributions reported (since 2000, more than 48 000 works published out of about 81 300 since 1900; results from SciFinder using "copper nanocatalysts in organic synthesis" as keywords). These huge efforts are mainly based on two key aspects: (i) copper is an Earth-abundant metal with low toxicity, leading to inexpensive and eco-friendly catalytic materials; and (ii) copper can stabilize different oxidation states (0 to +3) for molecular and nanoparticle-based systems, which promotes different types of metal-reagent interactions. This chemical versatility allows different pathways, involving radical or ionic copper-based intermediates. Thus, copper-based nanoparticles have become convenient catalysts, in particular for couplings (both homo- and hetero-couplings), transformations that are involved in a remarkable number of processes affording organic compounds, which find interest in different fields (medicinal chemistry, natural products, drugs, materials, etc.). Clearly, this richness in reactivity makes understanding the mechanisms more complex. The present review focuses on the analysis of reported contributions using monometallic copper-based nanoparticles as catalytic precursors applied in coupling reactions, paying attention to those shedding light on the reaction mechanism.

A New Scalable Synthesis of ELQ-300, ELQ-316, and other Antiparasitic Quinolones

The Endochin-Like Quinolone (ELQ) compound class may yield effective, safe treatments for a range of important human and animal afflictions. However, to access the public health potential of this compound series, a synthetic route needed to be devised that lowers costs and is amenable to large scale production. In the new synthetic route described here, a substituted β-keto ester, formed by an Ullmann reaction and subsequent acylation, is reacted with an aniline via a Conrad-Limpach reaction to produce 3-substituted 4(1H)-quinolones such as ELQ-300 and ELQ-316. This synthetic route, the first described to be truly amenable to industrial scale production, is relatively short (5 reaction steps), does not require palladium, chromatographic separation or protecting group chemistry, and may be performed without high vacuum distillation.