O-arylation Reaction Research Articles

Low-Cost, Safe, and Anion-Flexible Method for the Electrosynthesis of Diaryliodonium Salts.

An electrochemical approach toward the synthesis of diaryliodonium salts based on anodic C-I coupling between aryl iodides and arenes is presented. In contrast to previous protocols, our method requires no chemical oxidants, strong acids, or fluorinated solvents. A further advantage is that by use of the appropriate supporting electrolyte, the counterion of choice can be introduced, which is time- and cost-saving as compared to postsynthesis ion exchange. This "anion-flexibility" is particularly interesting when considering the pronounced effect of the counterion on the reactivity of diaryliodonium species in aryl transfer reactions. The scope of our method comprises 24 examples with isolated yields of up to 99%. Scalability was demonstrated by the synthesis on a gram scale. Furthermore, it was shown that the diaryliodonium-containing post-electrolysis solution can be used without further workup as a reactive medium for O-arylation reactions. Finally, a series of para-substituted diaryliodonium compounds was studied using linear sweep voltammetry on a microelectrode and analyzed with respect to the influence of the electronic structure on the redox behavior.

O-arylation reaction over lanthanide metal–organic framework: Synthesis, structure and catalytic reaction

Two novel lanthanide based two-dimensional metal-organic framework (MOF) compounds [Tb(NDC)(NO3)(DMA)2]n (MOF-1) and [Ho(NDC)(NO3)(DMA)2]n (MOF-2) [H2NDC=2,6-naphthalenedicarboxylic acid and DMA=N,N-dimethylacetamide] have been synthesized following solvothermal route and structurally characterized. Structural analysis reveals that both the compounds are crystallized in the orthorhombic crystal system with space group Pbca. MOFs feature a “paddle-wheel” (PW) type core building units which are constructed via carboxylato oxygen coordination with lanthanide atoms. 2D lanthanide based MOFs consist of paddle-wheel building block are rare in the literature. MOF-1 and MOF-2 possess an octa-coordinated metal center. Apart from carboxylato groups, oxygen atoms of DMA and NO3− ions are also coordinated to metal centers. Paddle-wheel cores are interconnected to each other to give rise to layered network structure in both the cases. 2D layers are propagated parallel to bc plane and layers are stacked one upon another along the crystallographic a axis. Notably, both MOF-1 and MOF-2 are capable to catalyze O-arylation reaction efficiently under heterogeneous medium. However, amongst them, catalytic efficacy of MOF-1 towards O-arylation reaction is found to be better than that of MOF-2.

Efficient base- and ligand-free palladium catalysed O-arylation of phenols in choline chloride:triethanolamine as a reusable deep eutectic solvent.

In this paper, we present a novel and sustainable approach using choline chloride:triethanolamine as a green, efficient and reusable deep eutectic solvent (DES) for Pd-catalysed O-arylation reactions with Pd/BaSO4 (10%). By using the unique properties of DESs, we successfully achieved C-O bond formation without the need for additional solvents, bases and ligands. This solvent/catalyst system ([ChCl][TEA]2) functioned as a dual catalyst and solvent system, enabling fast and environmentally friendly C-O bond formation from phenol derivatives and electron-deficient aryl halides, leading to remarkable yields under mild reaction conditions. To identify and characterize this DES, we employed differential scanning calorimetry, thermogravimetric analysis, Fourier-transform infrared spectroscopy, refractive index, viscosity, the potential of hydrogen (pH) and conductivity measurements. One of the remarkable advantages of this DES system is its exceptional stability. This solvent/catalyst system exhibited high stability throughout the reaction cycles, showing no significant loss of activity. As a result, this DES and catalyst (Pd/BaSO4 (10%)) can be easily recycled and re-used for up to three consecutive cycles, making it an economically and environmentally attractive option for organic reactions. Our approach offers several key benefits, including simple catalyst preparation, quick reaction times and excellent production efficiency.

Copper(II)-polymer chelate grafted from magnetic mesoporous silica for the O-arylation of phenols via the Ullmann reaction

The present work describes the grafting of polymer-metal chelates (PMC) from Fe3O4@SBA-15 via the Surface Initiated-Atom Transfer Radical Polymerization (SI-ATRP) method. Fe3O4@SBA-15 were silylated by 2-bromo-2-methyl-N-(3-(trimethoxysilyl)propanamide (BTPAm) to give the surface-anchored ATRP initiator. Acrylamide (AAm) was polymerized from the Fe3O4@SBA-15 surface via the ATRP approach and trans-amidated with ethylenediamine to give poly(N-2-aminoethylacrylamide) grafted magnetic mesoporous silica, Fe3O4@SBA-g-PAE-AAm. The grafted chelating polymer ligand (CPL) was treated with an acetonitrile solution of Cu(OAc)2 to afford the Fe3O4@SBA-g-PAE-AAm-Cu(II). The grafted PMC was characterized by FT-IR, CP/MAS 13C NMR, thermo-gravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) analysis. The oxidation state of copper (+2) was confirmed using X-ray photoelectron spectroscopy (XPS). The catalytic activity of the grafted PMC was examined in the CO bond formation via the Ullmann-type O-arylation reaction between haloarenes and phenols after establishing the optimal reaction conditions. The excellent recyclability of the catalyst was shown by small deactivation over seven runs.

An Attractive and Comprehensive Review on C-O Bond Formation: Nanomagnetic Recoverable Catalysts to Access Diaryl Ethers via C-O Cross-coupling Reactions

Abstract: The simple separation of magnetic nanocatalysts from the reaction mixture using only an external magnet caused a huge revolution in catalysis, particularly in organic synthesis. Diaryl ethers (compounds containing (Ar-O-Ar linkages) are one of the most important and prominent compounds and are widely found in natural products and pharmaceutical and biological molecules. The C-O cross-coupling or O-arylation reactions of aryl halides with aromatic alcohols, especially phenols, is an important and straightforward strategy for the preparation of diaryl ethers. Due to the high importance of diaryl ethers in the pharmaceutical, chemical and medical fields, many efforts have been made for the synthesis of diaryl ethers through C-O cross-coupling aryl halides with aromatic alcohols, especially phenols based on using non-magnetic reusable catalysts. In this review, we carefully reviewed the synthesis of diaryl ethers and discussed the reaction conditions and product yields in each method.

Mechanistic Views on First-row Earth-Abundant Transition Metal Catalyzed Ullmann-type O-Arylation Reactions.

Transition metal-catalyzed reactions have attracted much attention in synthetic organic chemistry due to their important role in the formation of C-heteroatom bonds. Ullmann coupling has risen in prominence in recent decades owing to its utilization in the synthesis of biaryl ethers found in a wide range of natural products together with biologically essential molecules, including antibiotics and major industrial polymers. In this article we provide the current understanding of the theoretical aspects of the underlying mechanism of the Ullmann-type O-arylation reaction.

Copper-catalysed one-pot cascade reaction strategy for the synthesis of benzoxazole-2-acrylic acid and benzoxazole-2‑propanoic acid derivatives

A Cu-catalysed cascade strategy has been developed to synthesize benzoxazole-2-acrylic acid and benzoxazole-2‑propanoic acid derivatives in one pot by reacting 2-bromoaniline with maleic anhydride or succinic anhydride. The cascade cyclic anhydride ring opening followed by O-arylation reaction afforded the products in very good yields.

Blue-Emitting Ligand-Mediated Assembly of Rare-Earth MOFs toward White-Light Emission, Sensing, Magnetic, and Catalytic Studies.

New lanthanide carboxylate compounds with two- (2D) and three-dimensional (3D) structures have been prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as an organic linker. The compounds, [Ln(C14H8O6)(C7O3H4)·2H2O]·4(H2O), Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy and [Ln(C7O3H4)3·(C3H7ON)·(H2O)]·2(H2O)(C3H7NO), Ln = La, Ce, Pr, have two- and three-dimensional structures, respectively. In all compounds, lanthanide ions are connected together, forming a dimer, which is connected by the 2,5-BPTA ligand. In the two-dimensional structure, there are two 2,5-BPTA moieties present, and in the three-dimensional structure, there are three 2,5-BPTA moieties present. The lanthanide centers are nine-coordinated, the 2D structure has a tricapped trigonal prismatic arrangement, and the 3D structure has a monocapped distorted square antiprismatic arrangement. The Pr compound forms in both 2D and 3D structures, whose formation depends on the time of the reaction (2 days─2D and 5-6 days─3D). The ligand emits in the blue region, and using the characteristic emission of Eu3+ (red) and Tb3+ (green) ions, we achieve white light emission in the (Y0.96Tb0.02Eu0.02) compound. The overall quantum yield for the white light emission is 28%. The strong green luminescence of the Tb3+-containing compound was employed to selectively sense the Cr3+ and Fe3+ ions in aqueous solution with limits of detection (LODs) at 0.41 and 8.6 ppm, respectively. The Tb compound was found to be a good heterogeneous catalyst for the Ullman-type O-arylation reaction between phenol and bromoarene with yields of 95%. Magnetic studies on the Gd-, Tb-, and Dy-containing compounds showed weak exchange interactions within the dimeric Ln2 units. The present work demonstrates the many utilities of the rare-earth-containing MOFs, especially toward white-light emission, metal-ion sensing, and heterogeneous catalysis.

Effective synthesis of regular ladder-type oligo(p-phenol)s via intramolecular SNAr O-arylation reaction

A series of novel ladder-type O-heteroarenes containing benzofuran units were effectively synthesized from the precursors via intramolecular SNAr reaction between F and OH groups in the backbone. The key intramolecular SNAr reaction was catalyst-free and highly efficient, moreover, the accurate annulation of fluorine atom ensured the regularity of the structure. We could smoothly obtain the ladder-type oligomer with seven oxygen bridges. The successes of the ladder-type oligomers also demonstrated the feasibility for preparing other regular oligomers and polymers with oxygen bridges.

Cover Feature: Exogenous Ligand‐Free Nickel‐Catalyzed Carboxylate O‐Arylation: Insight into NiI/NiIII Cycles (ChemCatChem 18/2022)

The Cover Feature shows the novel exogeneous ligand-free nickel-catalyzed coupling of aryl halides and carboxylic acids. In their Research Article, J. N. H. Reek, M. Tromp, T. J. Korstanje and co-workers provide insight into the competition between productive catalysis and deleterious pathways in the commonly proposed self-sustained NiI/NiIII catalytic cycle. Spectroscopic studies of the exogeneous ligand-free carboxylate O-arylation reaction unveiled the resting state of the nickel catalyst, the crucial role of the alkylamine base and the formation of an off-cycle NiINiII dimer upon reduction. More information can be found in the Research Article by J. N. H. Reek, M. Tromp, T. J. Korstanje and co-workers.

Unravelling the mechanism of cobalt (II) catalyzed O-arylation reaction between aryl halides and phenols: A DFT study

A detailed theoretical investigation into the mechanism of the cobalt (II) catalyzed O-arylation reaction of phenols with aryl iodides has been carried out with the aid of the Density Functional Theory method at the UB3LYP-D3 level of theory. The naturally occurring amino acid, l-valine was taken as the ancillary ligand for modeling the reaction mechanism. A tetrahedral, l-valine ligated cobalt (II) phenoxide complex in the quartet state, was found to be the active catalytic species. Unlike the Cu-catalyzed C-X (X = O, S, N) cross-coupling and Co-catalyzed CN coupling, the reaction proceeds through a facile σ – bond metathesis mechanism through the concerted breaking of Csp2 – I bond and the formation of Csp2 – O bond. The high reaction barrier (33.60 kcal/mol) obtained for the model system agrees with the experimental requirement of an elevated temperature [1]. To rationalize the experimentally observed selectivity of electron-deficient aryl iodides, we have investigated the electronic effects of various functional groups in the substrate molecules on the activation barrier of the reaction. This was contemplated by using Hammett correlation studies and Frontier Molecular Orbital analysis (FMO). The FMO analysis suggested that substitution by electron-withdrawing groups (EWG) at the para-position of the aryl iodides, decreases the LUMO energy, thereby decreasing the activation barrier of the reaction. However, in the case of substitution at the para-position of the phenolic moiety in the cobalt-phenoxide complex, the electron-rich groups are more favorable than the electron-withdrawing groups due to the rise in the HOMO energy of the substrate by the former. Thus, the present study can throw light on designing better catalytic systems for O-arylation reactions.

Suzuki−Miyaura coupling and O−arylation reactions catalysed by palladium(II) complexes of bulky ligands bearing naphthalene core, Schiff base functionality and biarylphosphine moiety

Schiff bases L1 [i.e., 2-(diphenylphosphino)-N-(naphthalen-1-ylmethylene)ethanamine], L2 [i.e., 2- (diphenylphosphino)-N-(naphthalen-2-ylmethylene)ethanamine], L3 [i.e., 2-(1-(2-(diphenylphosphino)ethylim- ino)ethyl)naphthalen-1-ol] and L4 [i.e., 2-((2-(diphenylphosphino)ethylimino)methyl)naphthalen-1-ol] have been synthesized using a straightforward methodology which involves a condensation reaction between H2N−CH2−CH2−PPh2 and appropriate carbonyl compound. Due to the presence of diphenylphosphine (−PPh2) moiety and >C = N− functionality, these compounds behave as ligands and undergo complexation reaction with palladium on treatment with Na2PdCl4 to yield the palladium(II) complexes (1–4). Ligands as well as complexes have been characterized using standard NMR spectroscopic techniques. ESI−MS and single crystal X−ray diffraction studies corroborate the structures of complexes. Crystal structures of complexes 1−3 reveal clearly that the geometry around Pd centre is distorted square planar. Ligands L1 and L2 are coordinated to Pd centre in bidentate (P, N type) mode, however, L3 and L4 act as a tridentate (P,N,O type) ligand and bind with metal in anionic mode. The Pd P and Pd N bond distances in complexes 1−3 are in the ranges 2.204−2.212 Å and 2.023−2.072 Å, respectively. Complex 3 [i.e., PdCl(L3−H)] also has a Pd-O bond, the length of which is found to be 2.009(3) Å. All the complexes have potential for catalysing O-arylation (C-O coupling) of phenol and Suzuki-Miyaura coupling (SMC) reactions. Both bromoarenes and chloroarenes can be used as substrates in Suzuki coupling and converted into biaryl derivatives. For O-arylation reactions of phenol, bromoarenes are used as arylating agents. For catalysis of such reactions (i.e., C-O coupling), high (0.1 mol%) catalyst loading is required. However, Suzuki reactions require low (0.001 mol%) loading of catalysts to occur with bromoarenes and give the products. The high potential of the complexes is also evident from the fact that they also convert different aryl chlorides into the coupled products in Suzuki coupling. 31P{1H} NMR data reveal that the electronic environments of nuclei of phosphorous donors are closely similar in all the four ligands. Similar magnitude of deshielding of the 31P{1H} signals in all the complexes indicate that, while forming the dative bond, the P donor of all the ligands transfer the electron density to the palladium to a similar extent. Hence, the electronic effects created by the ligands through the phosphorous donor are similar in all the complexes. Therefore, it is inferred that variation in their catalytic performance is because of difference in the binding mode of the ligand and/or minor alteration in the architecture of organic ligand. Amongst them, complex 2 shows the highest catalytic activity, and the least active catalyst is complex 3 for C-C coupling reactions. For C-O coupling reactions, the efficiencies of complexes 1 and 2 are slightly higher than those of complexes 3 and 4.

Palladium complex of sulphated schiff base with ortho-vanillin as catalyst for O-arylation of phenol

Organochalcogen compounds due to their hassle-free synthesis and air and moisture insensitive nature have attracted substantial attention in scientific world. They have profound applications in the development of catalytic systems that have emerged as efficient catalysts in various chemical transformations. Organochalcogen ligands have contributed to the backbone of several catalytic systems used for O-arylation reaction which is an effective tool for the synthesis of diaryl ether substituents. Synthesis of several bioactive compounds rely on this method. A thioether ligand L1 has been prepared by reaction of 3-(chloropropyl)amine hydrochloride with the insitu generated PhSNa. The L1 has been condensed with o-vanillin to synthesize ligand L2 having imine functionality. The structure of ligand L2 has been authenticated using proton and carbon-13 NMR techniques. The synthesis of an efficient N, S coordinated bidentate novel palladium complex 1 ([Pd(L2)Cl2]), by the reaction of ligand L2 with [PdCl2(CH3CN)2] in chloroform-hexane system has been carried out. The structure of 1 has also been corroborated by 1H ,13C{1H} NMR and mass spectroscopic techniques. Its catalytic potential has been tested for etherication of various aryl bromides with phenol. Cheaply available aryl chlorides have also been coupled to determine the efficiency of Pd(II) complex 1. The complex 1 gave good yields while exhibiting excellent tolerance towards electronically diverse aryl halides with 0.5 mol% catalyst loading. The nature of catalysis has been found to be purely homogeneous on conducting mercury and triphenylphosphine poisoning tests.

An advancement in the synthesis of nano Pd@magnetic amine-Functionalized UiO-66-NH2 catalyst for cyanation and O-arylation reactions

The magnetic MOF-based catalytic system has been reported here to be an efficient catalyst for synthesis of benzonitriles and diarylethers of aryl halides under optimal conditions. The MOF catalyst was built based on magnetic nanoparticles and UiO-66-NH2 which further modified with 2,4,6-trichloro-1,3,5-triazine and 5-phenyl tetrazole at the same time and the catalyst structure was confirmed by various techniques. This new modification has been applied to increase anchoring palladium into the support. Furthermore, the products’ yields were obtained in good to excellent for all reactions under mild conditions which result from superior activity of the synthesized heterogeneous catalyst containing palladium. Also, the magnetic property of the MOF-based catalyst makes it easy to separate from reaction mediums and reuse in the next runs.

An efficient, cost-effective, and magnetically recoverable copper catalyst for O-arylation of phenols with aryl halides in choline chloride-based deep eutectic solvents

Silica-coated magnetite nanoparticles were functionalized with aminopropylsilyl groups and then condensed with 2-benzoylthiophene to produce a NS Schiff base chelating ligand for complexation of Cu (II) species. Characterization of the synthesized nanocomposite was performed by several spectroscopic and microscopic analyses to reveal its physical and chemical properties. It was applied as an efficient heterogeneous catalyst in promoting O-arylation reaction of phenols with aryl halides for the synthesis of diaryl ethers using deep eutectic solvents (DESs) based on choline chloride as reaction media. The catalyst and DES could be easily recycled up to five times without a significant effect on the reaction progress. The use of green and recoverable reaction medium, easy work-up, easy separation of the catalyst with the assistance of an external magnetic field, short reaction times, and high yields of products are the main merits of this protocol.

Thermally stable and robust gadolinium-based metal-organic framework: Synthesis, structure and heterogeneous catalytic O-arylation reaction

Hydrothermal treatment of gadolinium nitrate and 2,6-naphthalenedicarboxylic acid (H2NDC) afforded a new metal-organic framework compound, {[Gd4(NDC)6(H2O)6]·2H2O}n(1). Compound 1 has been characterized by single-crystal X-ray crystallography, elemental analysis, FT-IR spectroscopy, therrmogravimetric analysis (TGA) and powder X-ray diffraction analysis. It is crystallized in the monoclinic system with the P21/n space group. Four crystallographically distinct Gd (III) centres are interconnected with each other through bridged carboxylato oxygen atoms and water molecules to form tetranuclear secondary building units, which are further connected through the carboxylato ligand and the network propagates along the crystallographic ac plane to form a 2D structure. Subsequent reinforcement from the remaining carboxylato oxygen atoms gives rise to a robust 3D framework structure. Thermogravimetric analysis demonstrates that compound 1 is fairly stable after dehydration under a nitrogen atmosphere.Notably, compound 1 is capable of catalyzing the O-arylation reaction efficiently between substituted phenols and bromoarene under heterogeneous conditions at 80 °C to afford unsymmetrical diarylethers.

N- and O-arylation of pyridin-2-ones with diaryliodonium salts: base-dependent orthogonal selectivity under metal-free conditions.

Metal-free N- and O-arylation reactions of pyridin-2-ones as ambident nucleophiles have been achieved with diaryliodonium salts on the basis of base-dependent chemoselectivity. In the presence of N,N-diethylaniline in fluorobenzene, pyridin-2-ones were very selectively converted to N-arylated products in high yields. On the other hand, the O-arylation reactions smoothly proceeded with the use of quinoline in chlorobenzene, leading to high yields and selectivities. In these methods, a variety of pyridin-2-ones in addition to pyridin-4-one and a set of diaryliodonium salts were accepted as suitable reaction partners.

Anchored N,O-Cu complex over Fe3O4@SiO2 as a highly efficient and reusable catalyst for C[sbnd]O coupling reaction

A novel heterogeneous catalyst was developed via the immobilization of a copper complex by covalent anchoring of the ligand on the surface of magnetic nano particles. The catalyst was characterized by various techniques including Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron micrograph (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), a vibrating sample magnetometer (VSM) and inductively coupled plasma (ICP) spectroscopy. The prepared catalyst demonstrated high catalytic activity, stability, reproducible dispersibility, and recycability in the O-arylation reactions. Moreover, the catalyst could be easily recovered under the outside magnetic field and reused without noticeable decreasing in its catalytic performance upon five consecutive runs.

Evolution of a Strategy for the Enantioselective Total Synthesis of (+)-Psiguadial B.

(+)-Psiguadial B is a diformyl phloroglucinol meroterpenoid that exhibits antiproliferative activity against the HepG2 human hepatoma cancer cell line. This full account details the evolution of a strategy that culminated in the first enantioselective total synthesis of (+)-psiguadial B. A key feature of the synthesis is the construction of the trans-cyclobutane motif by a Wolff rearrangement with in situ catalytic, asymmetric trapping of the ketene. An investigation of the substrate scope of this method to prepare enantioenriched 8-aminoquinolinamides is disclosed. Three routes toward (+)-psiguadial B were evaluated that featured the following key steps: (1) an ortho-quinone methide hetero-Diels-Alder cycloaddition to prepare the chroman framework, (2) a Prins cyclization to form the bridging bicyclo[4.3.1]decane system, and (3) a modified Norrish-Yang cyclization to generate the chroman. Ultimately, the successful strategy employed a ring-closing metathesis to form the seven-membered ring and an intramolecular O-arylation reaction to complete the polycyclic framework of the natural product.

Access to 8-Azachromones via Activation of C-H in N-Oxides.

A concise and practical synthetic method has been developed for 8-azachromones, including 8-azaflavones, which have emerged as a promising class of compounds. Using commercially available nicotinates as the starting material, 8-azachromones were obtained in only three steps. The key intramolecular O-arylation reaction was achieved by nucleophilic attack of enolates to C2 of N-oxides under PyBrop or Ac2O activation conditions. These studies provide the basis for the access to 8-azachromones, enabling future work including the discovery and development of novel chromonoid drugs or other functional materials.