Metal-free arylation of oxygen nucleophiles with diaryliodonium salts

Auxiliary strategy for the general and practical synthesis of diaryliodonium(III) salts with diverse organocarboxylate counterions

Diaryliodonium(III) salts are versatile reagents that exhibit a range of reactions, both in the presence and absence of metal catalysts. In this study, we developed efficient synthetic methods for the preparation of aryl(TMP)iodonium(III) carboxylates, by reaction of (diacetoxyiodo)arenes or iodosoarenes with 1,3,5-trimethoxybenzene in the presence of a diverse range of organocarboxylic acids. These reactions were conducted under mild conditions using the trimethoxyphenyl (TMP) group as an auxiliary, without the need for additives, excess reagents, or counterion exchange in further steps. These protocols are compatible with a wide range of substituents on (hetero)aryl iodine(III) compounds, including electron-rich, electron-poor, sterically congested, and acid-labile groups, as well as a broad range of aliphatic and aromatic carboxylic acids for the synthesis of diverse aryl(TMP)iodonium(III) carboxylates in high yields. This method allows for the hybridization of complex bioactive and fluorescent-labeled carboxylic acids with diaryliodonium(III) salts.

Diversification of Complex Diaryl Ethers via Diaryliodonium Intramolecular Aryl Rearrangement

In this study, we present an efficient site-selective O-arylation method applicable to a broad range of complex arenes involving intramolecular aryl rearrangement. The reaction was facilitated by diaryliodonium salts bearing vicinal trifluoromethanesulfonate (OTf) groups. The procedure was initiated with selective C-H bond activation of arenes, which were then converted into diaryl ethers through nucleophilic aromatic substitution (SNAr). This synthetic method successfully affords complex diaryl ether derivatives, showcasing its practicality for the diversification of functionalized arenes and pharmaceutical agents.

Convenient Synthesis of Salicylanilide Sulfonates from 1,2,3-Benzotriazin-4(3H)-ones and Organosulfonic Acids via Denitrogenative Cross-Coupling

An efficient and straightforward approach to synthesize salicylanilide aryl and alkyl sulfonates from 1,2,3-benzotriazin-4(3H)-ones and organosulfonic acids is described. This protocol is operationally simple and scalable, exhibits a broad substrate scope with high functional group tolerance, and affords the desired products in good to high yield. Application of the reaction is also demonstrated by converting the desired product to synthetically useful salicylamides in high yields.

Utilization of Aryl(TMP)iodonium Salts for Copper-Catalyzed N-Arylation of Isatoic Anhydrides: An Avenue to Fenamic Acid Derivatives and N,N'-Diarylindazol-3-ones

Herein, we report a general method for copper-catalyzed N-arylation of isatoic anhydrides with unsymmetrical iodonium salts at room temperature. The developed catalytic protocol is mild and operationally simple, and aryl(TMP)iodonium trifluoroacetate is employed as the arylating partner. The methodology offers the broad applicability of both structurally and electronically diverse aryl groups from aryl(TMP)iodonium salts to access N-arylated isatoic anhydrides in moderate to excellent yields (53-92%). Moreover, the substituted isatoic anhydrides are equally compatible with the protocol too. To demonstrate the synthetic utilities of the N-arylation process, we also report an alternative approach for biologically relevant fenamic acid derivatives and N,N'-diarylindazol-3-ones in a one-pot step economical system. In addition, the scale-up synthesis of flufenamic acid is also illustrated.

The most common linkers in bioactive molecules and their bioisosteric replacement network

Structures of the large majority of bioactive molecules are composed of several rings that are decorated by substituents and connected by linkers. While numerous cheminformatics studies focusing on rings and substituents are available, practically nothing has been published about the third important structural constituent of bioactive molecules - the linkers. The current study attempts to fill this gap. The most common linkers present in bioactive molecules are identified, their properties analyzed and a method for linker similarity search introduced. The bioisosteric replacement network of linkers is generated based on a large corpus of structure-activity data from medicinal chemistry literature. The results are presented in a graphical form and the underlying data are also made available for download. This analysis is intended to help medicinal chemists to better understand the role of linkers, particularly heterocyclic rings in bioactive molecules and to select an optimal set of linkers in their future project.

Transition-Metal-Free O-Arylation of Alcohols and Phenols with S-Arylphenothiaziniums

Herein, we report the transition-metal-free O-arylation of alcohols and phenols with S-arylphenothiaziniums, which can be easily synthesized from boronic acids. Aryl substituents derived from arylboronic acids were selectively introduced into the hydroxy groups in alcohols and phenols, and a variety of aryl ethers were synthesized. This selectivity is supported by theoretical calculations.

Ultrasound Accelerated Expedient and Eco-Friendly Synthesis of Aryl Sulfonates Using I2 As Catalyst At Ambient Conditions

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Aryl sulfonates were developed by ssing an energy-saving and eco-friendly approach, through ultrasound-assisted coupling reaction of readily sodium sulfinates with N-hydroxyphthalimide, under metal-free and mild conditions within 10 min at room temperature.

The Preparation and Application of Diaryliodonium Salts Derived from Gemfibrozil and Gemfibrozil Methyl Ester

The diaryliodonium salts derived from gemfibrozil and gemfibrozil methyl ester were synthesized from ArI(OH)OTs or bis(4-methoxyphenyl)iodonium diacetate with good regioselectivity. These iodonium salts were successfully used in the derivatization of gemfibrozil or gemfibrozil methyl ester, including fluorination, alkynylation, aryl­ation, etherification, esterification, and iodination reactions.

Copper-assisted preparation of pyridinyl sulfonate esters from hydroxypyridines and sodium sulfinates

An efficient and powerful copper-assisted method for the effective conversion of a broad range of hydroxypyridines and sodium sulfinates into their corresponding pyridinyl tosylates was developed. Key features of this base- and ligand-free protocol include using the cheap and readily available CuBr2 as a medium and the use of sodium sulfinates as formal sulfonylation reagents. A variety of functional pyridinyl tosylates could be formed with good yields, which can easily be converted into C-C and C-N bond-containing compounds.

Diaryliodonium(III) Salts in One-Pot Double Functionalization of C–IIII and ortho C–H Bonds

Since the 1950s, diaryliodonium(III) salts have been demonstrated to participate in various arylation reactions, forming aryl–heteroatom and aryl–carbon bonds. Incorporating the arylation step into sequential transformations would provide access to...

Diaryliodonium Salt-Based Synthesis of N-Alkoxyindolines and Further Insights into the Ishikawa Indole Synthesis

A diaryliodonium salt-based strategy enabled the first systematic synthesis of rarely accessible N-alkoxyindolines. Mechanistic analyses suggested that the reaction likely involves reductive elimination of iodobenzene from iodaoxazepine via a four-membered transition state, followed by Meisenheimer rearrangement. Substrates with N-carbamate protection afforded indole in a manner similar to that of the Ishikawa indole synthesis. Preinstallation of a stannyl group as an iodonium salt precursor greatly expanded the substrate scope, and further mechanistic insights are discussed.

Preparation and Synthetic Application of Naproxen-Containing Diaryliodonium Salts

The synthesis of naproxen-containing diaryliodonium salts has been realized from naproxen methyl ester and ArI(OH)OTs activated by trimethylsilyl trifluoromethanesulfonate (TMSOTf) in a solvent mixture comprising dichloromethane and 2,2,2-trifluoroethanol (TFE). Those iodonium salts have been successfully used in the functionalization of an aromatic ring of naproxen methyl ester, including fluorination, iodination, alkynylation, arylation, thiophenolation, and amination and esterification reactions. Moreover, further hydrolysis of the obtained 5-iodo-naproxen methyl ester afforded 5-iodo-naproxen.

Heteroaryliodonium(III) Salts as Highly Reactive Electrophiles

In recent years, the chemistry of heteroaryliodonium(III) salts has undergone significant developments. Heteroaryliodonium(III) salts have been found to be useful synthetic tools for the transfer of heteroaryl groups under metal-catalyzed and metal-free conditions for the preparation of functionalized heteroarene-containing compounds. Synthetic transformations mediated by these heteroaryliodonium(III) salts are classified into two categories: (1) reactions utilizing the high reactivity of the hypervalent iodine(III) species, and (2) reactions based on unique and new reactivities not observed in other types of conventional diaryliodonium salts. The latter feature is of particular interest and so has been intensively investigated in recent decades. This mini-review therefore aims to summarize the recent synthetic applications of heteroaryliodonium(III) salts as highly reactive electrophiles.

The Diaryliodonium(III) Salts Reaction With Free-Radicals Enables One-Pot Double Arylation of Naphthols

The chemoselective reaction of the C- followed by the O-centered naphthyl radicals with the more electron-deficient hypervalent bond of the diaryliodonium(III) salts is described. This discovered reactivity constitutes a new activation mode of the diaryliodonium(III) salts which enabled a one-pot doubly arylation of naphthols through the sequentialC s p 2 -C s p 2 /O-C s p 2 bond formation. The naphthyl radicals were generated in the reaction by the tetramethylpiperidinyl radical (TMP·) which resulted from the homolytic fragmentation of the precursor TMP2O. Experimental and DFT calculations provided a complete panorama of the reaction mechanism.

Copper-Catalyzed Selective Arylation of Nitriles with Cyclic Diaryl Iodonium Salts: Direct Access to Structurally Diversified Diarylmethane Amides with Potential Neuroprotective and Anticancer Activities

A novel, simple, and high-yielding approach for the preparation of diarylmethane amide derivatives has been developed by reacting cyclic diaryl iodonium salts with nitriles using CuCl as a catalyst. The procedure is efficient with high atom economy and a wide substrate range. Importantly, selective arylation of nitriles was obtained without affecting the phenyl amino/hydroxyl groups. Furthermore, two of the diarylmethane amides (3k, 3s) displayed excellent neuroprotective and anticancer activities.

C2-H Arylation of Indoles Catalyzed by Palladium-Containing Metal-Organic-Framework in γ-Valerolactone

An efficient and selective procedure was developed for the direct C2-H arylation of indoles using a Pd-loaded metal-organic framework (MOF) as a heterogeneous catalyst and the nontoxic biomass-derived solvent γ-valerolactone (GVL) as a reaction medium. The developed method allows for excellent yields and C-2 selectivity to be achieved and tolerates various substituents on the indole scaffold. The established conditions ensure the stability of the catalyst as well as recoverability, reusability, and low metal leaching into the solution.

Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3',2'-e]pyridines (BBZFPys)

A series of optically active bisbenzofuro[2,3-b:3’,2’-e]pyridine (BBZFPy) derivatives was synthesized starting with the readily available (S)- and (R)-1,1’-bi-2-naphthols through a palladium-catalyzed multiple intramolecular C–H/C–H coupling as the key ring-closure step. The effect of terminal tert-butyl substituents on the BBZFPy skeleton was systematically investigated to uncover a unique aggregation-induced enhancement of CPL characteristics in the solid state. The crystal structures of the coupling products were also evaluated by single crystal X-ray analysis and the well-ordered intermolecular stacking arrangements appeared to be responsible for the enhanced CPL.

Lewis Acidity Scale of Diaryliodonium Ions toward Oxygen, Nitrogen, and Halogen Lewis Bases

Equilibrium constants for the associations of 17 diaryliodonium salts Ar₂I⁺X^- with 11 different Lewis bases (halide ions, carboxylates, p-nitrophenolate, amines, and tris(p-anisyl)phosphine) have been investigated by titrations followed by photometric or conductometric methods as well as by isothermal titration calorimetry (ITC) in acetonitrile at 20 °C. The resulting set of equilibrium constants K_I covers 6 orders of magnitude and can be expressed by the linear free-energy relationship lg K_I = s_I LA_I + LB_I, which characterizes iodonium ions by the Lewis acidity parameter LA_I, as well as the iodonium-specific affinities of Lewis bases by the Lewis basicity parameter LB_I and the susceptibility s_I. Least squares minimization with the definition LA_I = 0 for Ph₂I⁺ and s_I = 1.00 for the benzoate ion provides Lewis acidities LA_I for 17 iodonium ions and Lewis basicities LB_I and s_I for 10 Lewis bases. The lack of a general correlation between the Lewis basicities LB_I (with respect to Ar₂I⁺) and LB (with respect to Ar₂CH⁺) indicates that different factors control the thermodynamics of Lewis adduct formation for iodonium ions and carbenium ions. Analysis of temperature-dependent equilibrium measurements as well as ITC experiments reveal a large entropic contribution to the observed Gibbs reaction energies for the Lewis adduct formations from iodonium ions and Lewis bases originating from solvation effects. The kinetics of the benzoate transfer from the bis(4-dimethylamino)-substituted benzhydryl benzoate Ar₂CH-OBz to the phenyl(perfluorophenyl)iodonium ion was found to follow a first-order rate law. The first-order rate constant k_obs was not affected by the concentration of Ph(C₆F₅)I⁺ indicating that the benzoate release from Ar₂CH-OBz proceeds via an unassisted S_N1-type mechanism followed by interception of the released benzoate ions by Ph(C₆F₅)I⁺ ions.

Base-Mediated O-Arylation of Alcohols and Phenols by Triarylsulfonium Triflates

A mild and efficient protocol for O-arylation of alcohols and phenols (ROH) by triarylsulfonium triflates was developed under transition-metal-free conditions. Various alcohols, including primary, secondary and tertiary, and phenols bearing either electron-donating or electron-withdrawing groups on the aryl rings were smoothly converted to form the corresponding aromatic ethers in moderate to excellent yields. The reactions were conducted at 50 or 80 °C for 24 h in the presence of a certain base and showed good functional group tolerance. The base-mediated arylation with asymmetric triarylsulfonium salts could selectively transfer the aryl groups of sulfoniums to ROH, depending on their inherent electronic nature. The mechanistic studies revealed that the reaction might proceed through the nucleophilic attack of the in situ formed alkoxy or phenoxy anions at the aromatic carbon atoms of the C-S bonds of triarylsulfonium cations to furnish the target products.

Synthesis of Uracil-Iodonium(III) Salts for Practical Utilization as Nucleobase Synthetic Modules

Iodonium(III) salts bearing uracil moieties have recently appeared in the literature, but their structural scope and utilization are limited because of their hygroscopic characteristics. In this study, we describe our detailed investigations for synthesizing a series of uracil iodonium(III) salts derived with various structural motifs and counterions. These new compounds have been utilized as attractive synthetic modules in constructing functionalized nucleobase and nucleosides.

Palladium-Catalyzed C-H Bond Functionalization Reactions Using Phosphate/Sulfonate Hypervalent Iodine Reagents

A new and operationally simple approach for palladium-catalyzed C-H functionalization reactions utilizing an organophosphorus/sulfonate hypervalent iodine reagent as both an oxidant and the source of a functional group has been developed. Through this method, the oxidative phosphorylation-, sulfonation-, and hydroxylation of unactivated benzyl C(sp³)-H bonds, along with the hydroxylation and arylation of aryl C(sp²)-H bonds, are successfully realized under mild conditions and with excellent site-selectivity. The versatile C-OSO₂R bond provides a platform for a wide array of subsequent diversification reactions.

Transition-Metal-Free Aryl-Aryl Cross-Coupling: C-H Arylation of 2-Naphthols with Diaryliodonium Salts

Transition-metal-free regioselecitive C-H arylation of 2-naphthols with diaryliodonium salts has been developed. The reaction proceeds under very simple experimental conditions and affords a range of products with various substitution patterns. The method allows for the incorporation of electron-deficient aryls, which complements well currently existing metal-free aryl-aryl cross-couplings of phenols that have been so far restricted to the introduction of electron-rich aryl moieties. The mechanism of the reaction was studied by means of DFT calculations, demonstrating that the C-C bond formation occurs via a dearomatization of 2-naphthol substrate, followed by a subsequent rearomatization by tautomerization. The computations show that the use of a low polarity solvent and an insoluble inorganic base is key to securing the high selectivity of the C-C coupling over a competing C-O arylation pathway, by preventing the incipient deprotonation of 2-naphthol.

Metal-free formal synthesis of phenoxazine

A transition metal-free formal synthesis of phenoxazine is presented. The key step of the sequence is a high-yielding O-arylation of a phenol with an unsymmetrical diaryliodonium salt to provide an ortho-disubstituted diaryl ether. This species was cyclized to acetylphenoxazine in moderate yield. The overall yield in the three-step sequence is 72% based on recovered diaryl ether. An interesting, unusually stable iodine(III) intermediate in the O-arylation was observed by NMR and could be converted to the product upon longer reaction time.

One-pot preparation of 4-aryl-3-bromocoumarins from 4-aryl-2-propynoic acids with diaryliodonium salts, TBAB, and Na2S2O8

Various 4-aryl-3-bromocoumarins were smoothly obtained in moderate yields in one pot by treating 3-aryl-2-propynoic acids with diaryliodonium triflates and K₂CO₃ in the presence of CuCl, followed by the reaction with tetrabutylammonium bromide (TBAB) and Na₂S₂O₈. The obtained 3-bromo-4-phenylcoumarin was transformed into 4-phenylcoumarin derivatives bearing C-H, C-S, C-N, and C-C bonds at 3-position.

Stabilized pyrrolyl iodonium salts and metal-free oxidative cross-coupling

Pyrrole-aryl derivatives are important due to their unique biological activities in medicinal chemistry. We now report a new oxidative biaryl coupling for pyrroles and indoles toward various arenes using a hypervalent iodine reagent and an appropriate stabilizer for pyrrolyl iodonium intermediates. The reactions readily provide a variety of desired coupling products in good yields.