Potassium Aryltrifluoroborates Research Articles

Palladium catalyzed selective arylation of B(4)-H of o-carboranes with potassium aryltrifluoroborate

A palladium catalyzed selective arylation of B(4)-H of 9-amide-o-carborane with potassium aryltrifluoroborate has been developed. A series of B(4)-Ar-B(9)-amide-o-carborane derivatives decorated with diverse active groups have been synthesized with moderate to good yields as well as excellent selectivity. This work represents an unprecedented protocol for selective arylation of o-carboranes with potassium aryltrifluoroborates.

Design, stereoselective synthesis, and antitumoral activity of combretastatin A-4 analogs

Combretastatin A-4 (CA-4) is a microtubule targeting agent, and it has a great advantage when compared to other compounds with a similar mechanism of action, such as vinca alkaloids, colchicine, podophillotoxin, and paclitaxel: its simpler structure. In this work, the stereoselective synthesis and antiproliferative activity of stable CA-4 analogs, obtained from the cross-coupling reaction between vinyl tellurides and potassium aryltrifluoroborates is described. The method is simple, fast, and general, allowing further applications for the synthesis of more complex compounds.

(Ph3P)AuCl-catalyzed homocoupling of arylboronic acids under benchtop conditions: Synthesis of biphenyls

(Ph3P)AuCl was discovered to be a powerful catalyst in the homocoupling of arylboronic acids and potassium aryltrifluoroborates for the synthesis of symmetrical biaryls. The reactions take place under benchtop reaction conditions in 96% EtOH at temperatures between rt and 50 °C with no exclusion of air or humidity, in the presence of F-TEDA (Selectfluor™) as an oxidant. The procedure is very functional group tolerant, and affords the corresponding biaryls in high yields with large substrate scope (26 examples).

Introducing Trifluoromethoxyarenes as Halide Surrogates in Mechanochemical Realizations of Ni‐catalyzed Cross‐coupling Reactions

AbstractSince the introduction of the TM‐catalyzed cross‐couplings their scope of starting materials has been growing systematically, allowing for more flexible design of synthetic routes with the coupling as a key step, particularly late‐stage modifications. Herein we present the use of trifluoromethoxyarenes as halide surrogates in Ni‐catalyzed couplings with arylboronic acids, potassium aryl trifluoroborates and aryl trialkoxysilanes, under mechanochemical conditions. In total, 22 biphenyl structures were obtained in good yields. Successful gram scale experiments confirm the usefulness of our protocol. The developed transformations’ mechanism was discussed in relation to the experimental and literature data and DFT calculations. The unusual reactivity of potassium benzoyltrifluoroborates was uncovered. 6 examples of resulting benzophenones were obtained in very good yields and the protocol was extended to gram scale. The described methods present a powerful tool when combined with the recent advances in organofluorine chemistry.

Selective functionalization of hindered meta-C–H bond of o-alkylaryl ketones promoted by automation and deep learning

<h2>Summary</h2> Selective functionalization of the sterically hindered aromatic <i>meta</i>-C–H bond is unprecedented and remains to be a major challenge. Promoted by automation-based high-throughput experimentation (HTE) and deep learning (DL), a novel strategy to functionalize the hindered <i>meta</i>-C–H bond is disclosed. With carbon dioxide as a traceless director, a one-pot three-step protocol was developed to achieve selective arylation of <i>o</i>-alkylaryl ketones at the hindered <i>meta</i> position. This novel strategy involved photo-induced C–H carboxylation, carboxyl group-directed Pd-catalyzed C–H functionalization, and microwave-assisted decarboxylation. With HTE and DL, a broad scope of substrates was explored (1,032 reactions) and a DL-based model (CMPRY) for reaction yield prediction was established. Two independent tests with unseen <i>o</i>-alkylaryl ketones and/or potassium aryltrifluoroborates were used to evaluate the model. The model gave excellent performances in predicting unseen reactions; mean absolute errors in yield were only 6.6% and 8.4%, suggesting its potential in synthetic application.

Suzuki–Miyaura Cross-Coupling Reaction with Potassium Aryltrifluoroborate in Pure Water Using Recyclable Nanoparticle Catalyst

AbstractThis paper describes the Suzuki–Miyaura cross-coupling reaction of aryl bromides with potassium aryltrifluoroborates in water catalyzed by linear polystyrene-stabilized PdO nanoparticles (PS-PdONPs). The reaction of aryl bromides having electron-withdrawing groups or electron-donating groups took place smoothly to give the corresponding coupling product in high yields. The catalyst recycles five times without significant loss of catalytic activity although a little bit increase in size of PdNPs was observed after the reaction.

Porphyrin N-Pincer Pd(II)-Complexes in Water: A Base-Free and Nature-Inspired Protocol for the Oxidative Self-Coupling of Potassium Aryltrifluoroborates in Open-Air.

Metalloporphyrins (and porphyrins) are well known as pigments of life in nature, since representatives of this group include chlorophylls (Mg-porphyrins) and heme (Fe-porphyrins). Hence, the construction of chemistry based on these substances can be based on the imitation of biological systems. Inspired by nature, in this article we present the preparation of five different porphyrin, meso-tetraphenylporphyrin (TPP), meso-tetra(p-anisyl)porphyrin (TpAP), tetrasodium meso-tetra(p-sulfonatophenyl)porphyrin (TSTpSPP), meso-tetra(m-hydroxyphenyl)porphyrin (TmHPP), and meso-tetra(m-carboxyphenyl)porphyrin (TmCPP) as well as their N-pincer Pd(II)-complexes such as Pd(II)-meso-tetraphenylporphyrin (PdTPP), Pd(II)-meso-tetra(p-anisyl)porphyrin (PdTpAP), Pd(II)-tetrasodium meso-tetra(p-sulfonatophenyl)porphyrin (PdTSTpSPP), Pd(II)-meso-tetra(m-hydroxyphenyl)porphyrin (PdTmHPP), and Pd(II)-meso-tetra(m-carboxyphenyl)porphyrin (PdTmCPP). These porphyrin N-pincer Pd(II)-complexes were studied and found to be effective in the base-free self-coupling reactions of potassium aryltrifluoroborates (PATFBs) in water at ambient conditions. The catalysts and the products (symmetrical biaryls) were characterized using their spectral data. The high yields of the biaryls, the bio-mimicking conditions, good substrate feasibility, evading the use of base, easy preparation and handling of catalysts, and the application of aqueous media, all make this protocol very attractive from a sustainability and cost-effective standpoint.

Catalytic Synthesis of Atropisomeric o-Terphenyls with 1,2-Diaxes via Axial-to-Axial Diastereoinduction.

Herein, we report a modular and convergent strategy for the assembly of atropisomeric o-terphenyls with 1,2-diaxes via palladium/chiral norbornene cooperative catalysis and axial-to-axial diastereoinduction. Readily available aryl iodides, 2,6-substituted aryl bromides, and potassium aryl trifluoroborates are used as the building blocks, laying the foundation for diversity-oriented synthesis of these scaffolds (46 examples). Other features include the unique axial-to-axial diastereoinduction mode, construction of two axes in a single operation, and step economy. DFT calculations are performed to rationalize the axial-to-axial diastereoinduction process. Synthetic utilities of this method in preparation of atropisomeric oligophenyls, chiral catalysts, and ligands are demonstrated.

Exploration of the Fluoride Reactivity of Aryltrifluoroborate on Selective Cleavage of Diphenylmethylsilyl Groups

The first known report on the fluoride catalytic reactivity of potassium aryltrifluoroborate is described. The fluoride reactivity of phenyltrifluoroborate was controlled by substituents on the trifluoroborate‐attached benzene, such as the methoxy group at the para‐position and the methyl group at the ortho‐position. In addition, the selective aryltrifluoroborate‐catalyzed cleavage of the diphenylmethylsilyl group was achieved.

Site-Selective Ruthenium-Catalyzed C-H Bond Arylations with Boronic Acids: Exploiting Isoindolinones as a Weak Directing Group.

Biologically relevant N-arylisoindolinones efficiently underwent arylation reactions under ruthenium catalysis via C-H bond functionalization. The reactions exclusively led to monoarylated products, and only ortho selectivity was observed in the aromatic ring connected to the nitrogen atom. Interestingly, no C-H bond functionalization was observed in the other benzene ring in the ortho position with respect to the carbonyl group. This ruthenium-catalyzed reaction displayed a high functional group tolerance, and it employed readily available and benchmark stable boronic acid and potassium aryltrifluoroborate derivatives as coupling partners. An appealing late-stage functionalization of indoprofen applying this methodology is showcased.

Transition-Metal-Free C-C, C-O, and C-N Cross-Couplings Enabled by Light.

Transition-metal-catalyzed cross-couplings to construct C-C, C-O, and C-N bonds have revolutionized chemical science. Despite great achievements, these metal catalysts also raise certain issues including their high cost, requirement of specialized ligands, sensitivity to air and moisture, and so-called "transition-metal-residue issue". Complementary strategy, which does not rely on the well-established oxidative addition, transmetalation, and reductive elimination mechanistic paradigm, would potentially eliminate all of these metal-related issues. Herein, we show that aryl triflates can be coupled with potassium aryl trifluoroborates, aliphatic alcohols, and nitriles without the assistance of metal catalysts empowered by photoenergy. Control experiments reveal that among all common aryl electrophiles only aryl triflates are competent in these couplings whereas aryl iodides and bromides cannot serve as the coupling partners. DFT calculation reveals that once converted to the aryl radical cation, aryl triflate would be more favorable to ipso substitution. Fluorescence spectroscopy and cyclic voltammetry investigations suggest that the interaction between excited acetone and aryl triflate is essential to these couplings. The results in this report are anticipated to provide new opportunities to perform cross-couplings.

Synthesis of heterobiaryls via Suzuki‐Miyaura coupling reaction of potassium aryltrifluoroborates with heteroaryl halides in aqueous systems

A variety of heterobiaryl compounds have been synthesized by the Suzuki‐Miyaura coupling reactions of heteroaryl halides with potassium aryltrifluoroborates. Pd (OAc)2 was found to be highly efficient for the Suzuki‐Miyaura coupling reactions of various heteroaryl halides with potassium aryltrifluoroborates in aqueous systems, delivering the corresponding heterobiaryl compounds in good to excellent yields.

Efficient Cross-Coupling Reaction of Aryltrifluoroborates and Aroyl Chlorides for the Synthesis of Fluorine Substituted Aromatic Ketones

The direct aroylation of ArCOPdCl with potassium aryltrifluoroborates establishes a new cross-coupling synthetic tool for the synthesis of various fluorine substituted benzophenones. The new microwave irradiated process is very efficient and produce high yield benzophenone products within minutes.

An Efficient Ligandless Palladium-catalyzed Protocol for Suzuki-Miyaura Coupling Reaction of Potassium Aryltrifluoroborates in Water

An efficient and ligandless catalytic system was developed for the Suzuki- Miyaura coupling reactions of potassium aryltrifluoroborates in pure water. Using TEAB as additives, Pd(OAc)2 was found to be very efficient for the Suzuki-Miyaura coupling of potassium aryltrifluoroborates with various aryl and heteroaryl bromides in pure water with Na2CO3 as a base, affording the desired products in moderate to excellent yields. Keywords: Suzuki-Miyaura coupling reaction, potassium aryltrifluoroborate, aryl bromide, heteroaryl bromide, water, palladium acetate.

Ligand-Free Bioinspired Suzuki-Miyaura Coupling Reactions using Aryltrifluoroborates as Effective Partners in Deep Eutectic Solvents.

Pd-catalyzed Suzuki-Miyaura cross-coupling between (hetero)aryl halides (Cl, Br, I) and versatile, moisture-stable mono- and bifunctional potassium aryltrifluoroborates proceeded efficiently and chemoselectively in air and under generally mild conditions; a catalyst loading as low as 1 mol % combined with Na2 CO3 as a base in choline chloride/glycerol (1:2) deep eutectic solvent (DES) was used as a sustainable and environmentally responsible medium. The catalyst, base, and DES were easily and successfully recycled up to six times with an E-factor as low as 8.74. Valuable biaryls and terphenyl derivatives were furnished in yields of up to 98 %; over 50 reactions were compared and discussed. The methodology was applied for the synthesis of the nonsteroidal anti-inflammatory drugs Felbinac and Diflunisal.

Oxygen-promoted Suzuki–Miyaura reaction of aryl fluorosulfates and potassium aryltrifluoroborates: Mild and efficient access to biaryls and terphenyls

A mild and efficient protocol has been developed for the Suzuki–Miyaura reaction of aryl fluorosulfates and potassium aryltrifluoroborates at room temperature. A series of biaryls can be prepared with excellent yields in this system and an aerobic atmosphere demonstrates a positive effect on the reactivity of the cross-coupling reactions. Additionally, this method can be extended to one-pot double Suzuki–Miyaura reactions, allowing the synthesis of various unsymmetrical terphenyls in moderate to good yields.

Iodide-Catalyzed Carbonylation–Benzylation of Benzyl Chlorides with Potassium Aryltrifluoroborates under Ambient Pressure of Carbon Monoxide

Tetra-N-butylammonium iodide (TBAI) catalyzed carbonylation–benzylation of unactivated benzyl chlorides with potassium aryltrifluoroborates using CO gas has been developed. This reaction is transition-metal free, is carried out under ambient pressure, and provides a wide range of 1,2,3-triarylpropan-1-one derivatives in high yields. The novel method represents a significant improvement over the traditional palladium-catalyzed carbonylation.

Systematic Consideration of Physicochemical Properties on Aryltrifluoroborate-Based Room-Temperature Ionic Liquids

Room-temperature ionic liquid (RTIL), which is the salt constructed of just cation and anion to be able to liquefy at ambient temperature, has fascinating characteristics such as negligible vapor pressure, wide liquidus temperature range, wide electrochemical window, and relatively-high ionic conductivity. Many applications using RTIL e.g., non-volatile electrolyte for energy storage devices, recyclable green solvent for electroplating, and a functional synthetic lubricant oil, have been proposed owing to RTIL’s interesting features.1 Another feature is the physicochemical properties and functionality can be roughly controlled by a combination of anion and cation. Creation of novel ionic species, especially anion, are really expected for further improvement. Recently we have focused on aryltrifluoroborate ([ArBF3]− (Figure 1)) because of the low surface charge density needed to decrease the lattice energy and the easy modification of [ArBF3]−. In present study, we investigated the effects on the physicochemical properties when RTIL structure was systematically changed by using the [ArBF3]− families with different substituents on the aromatic ring. RTILs used in this study were synthesized by a metathesis reaction using appropriate potassium aryltrifluoroborate (K[ArBF3]) prepared by the reported procedure2 and 1-butyl-3-methylimidazolium chloride ([C4mim]Cl). All electrochemical experiments were performed in a three-electrode cell. The working electrode was a glassy carbon disk (diameter: 1.0 mm), which was polished with an alumina suspension before use. A platinum wire (dimeter: 0.5 mm) was used as the counter electrode. The reference electrode was constructed by placing a Ag wire into a 6 mm diameter glass tube terminated with a vycor® glass and filling this tube with [C4mim][N(SO2CF3)2] containing 0.05 M Ag[N(SO2CF3)2]. All the experiments except viscosity measurement were carried out in an argon-filled-glove box (O2 and H2O < 1 ppm). Viscosity was measured by an electromagnetically spinning viscometer without any contamination. RTILs used in this study consist of [C4mim]+ cation and [ArBF3]− anion. The anionic species were non-substitutive phenyltrifluoroborate ([PhBF3]), (meta-fluorophenyl)trifluoroborate ([m-FC6H4BF3]), (meta-methoxyphenyl)trifluoroborate ([m-OMeC6H4BF3]), (meta-trifluoromethylphenyl)trifluoroborate ([m-CF3C6H4BF3]), and (meta-cyanophenyl)trifluoroborate ([m-CNC6H4BF3]). All the prepared RTILs showed favorable fluidity (< 294 mPa·s) and ionic conductivity (1.09 mS·cm−1 <) at ambient temperature (298 K). Electrochemical stability was estimated by a liner sweep voltammetry technique. Each scan was started from the open circuit potential, which was referred to Ag(I)/Ag redox system. The electrochemically stable potential range called electrochemical window (EW) is commonly used for the discussion of the electrochemical stability for electrolytes including RTILs. The linear sweep voltammograms recorded in the RTILs are shown in Figure 2, and the cathodic limiting potential (E c), the anodic limiting potential (E a) and electrochemical windows (EW = E a − E c) estimated from Figure 2 using the cut-off current density of ±0.1 mA·cm−2 are summarized in Table I. All the cathodic limiting potentials showed almost the same values (−2.80 ~ −2.97 V vs. Ag(I)/Ag) because of the same cationic species. On the other hand, the anodic stability was strongly dependent on the anionic species. For example, as shown in Figure 2, the anodic decomposition of [C4mim][m-OMeC6H4BF3] and non-substitutive [C4mim][PhBF3] initiates at 0.327 and 0.799 V vs. Ag(I)/Ag, respectively. In general, an anodic limiting potential is subject to HOMO energy of anion. Thus, [C4mim][m-OMeC6H4BF3], which possesses an electron-donating methoxy group (OMe), show the smaller EW (3.26 V) than that of non-substitutive [C4mim][PhBF3] (3.65 V) since the HOMO energy of [m-OMeC6H4BF3]− (−4.67 eV) is higher than that of [PhBF3]− (−4.94 eV). This means that RTILs with an electron-withdrawing group can display relatively large E a due to the lower HOMO energy than RTILs without any group. However, unexpected and intriguing results as described below were obtained. The small oxidation currents caused by the anion decomposition were recognized at 0.611 ~ 0.799 V in the RTILs with electron withdrawing groups: F; CF3; and CN. Interestingly oxidation current became almost zero up to 5.0 V once the small oxidation current flowed. We speculated that an electrochemically inactive film was formed on the electrode surface at the first oxidation wave. By using various analytical approaches such as IR spectroscopy, SEM observation, and EDX analysis, it was found that the film has a unique surface morphology and contains the elements derived from aryltrifluoroborate such as carbon and fluorine. 1. T. Torimoto, T. Tsuda, K. Okazaki, and S. Kuwabata, Adv. Mater., 22, 1196 (2010). 2. K. Iwasaki, K. Yoshii, S. Tsuzuki, H. Matsumoto, T. Tsuda, and S. Kuwabata, J. Phys. Chem. B, 120, 9468 (2016). Figure 1

Sequential O-Arylation/Lanthanide(III)-Catalyzed [3,3]-Sigmatropic Rearrangement of Bromo-Substituted Allylic Alcohols

Lanthanide(III)-catalyzed aryl-Claisen rearrangement of substrates bearing halo-substituted allyl groups, specifically 2-bromoallyl aryl ethers, afford ortho-2-bromoallylphenols. Aryl ether substrates were synthesized from brominated allylic alcohols via Mitsunobu reaction, Cu(II)-catalyzed arylation using potassium aryltrifluoroborate salts, or SNAr reaction. Aryl-Claisen rearrangements proceeded in moderate to excellent yields using Eu(III) catalysis. The alkenylbromide functionality remains intact, illustrating the compatibility of synthetically important alkenylhalides during C–O/C–C σ-bond migration processes. Subsequent derivatization of the ortho-2-bromoallylphenol products through O-alkylation or C-arylation/alkenylation via Suzuki–Miyaura cross-coupling demonstrate the potential to access densely-functionalized molecules.

A synthesis of biaryl ketones via the C–S bond cleavage of thiol ester by a Cu/Ag salt

Abstract We report the synthesis of biaryl ketones via an unprecedented copper/silver catalyzed acylative cross-coupling of thiol esters with either an arylboronic acid or a potassium aryltrifluoroborate. This new method proceeds without a requisite Pd-catalyst and Cu(I)TC mediator, and is efficient, versatile, operationally simple, and accommodating functionally diverse thiol esters, arylboronic acids, and potassium aryltrifluoroborates.