Pd-Catalyzed Decarboxylative Cross Coupling of Potassium Polyfluorobenzoates with Aryl Bromides, Chlorides, and Triflates

Mild Pd-Catalyzed Decarboxylative Cross-Coupling of Zinc(II) Polyfluorobenzoates with Aryl Bromides and Nonaflates: Access to Polyfluorinated Biaryls

We developed a Pd-catalyzed decarboxylative cross-coupling of zinc polyfluorobenzoates, which were used as precursors for producing zinc reagents in situ, with aryl bromides and nonaflates, providing a mild and efficient pathway for the synthesis of polyfluorinated biaryls. This protocol exhibits a broad substrate scope and excellent functional tolerance. Moreover, the versatility of this approach was demonstrated by the straightforward late-stage modification of drugs, biologically active molecules, and pesticides, indicating its potential significance in drug discovery.

Palladium-catalysed deaminative/decarboxylative cross-coupling of organoammonium salts with carboxylic acids

A palladium-catalysed carbon-carbon bond-forming reaction via deaminative/decarboxylative cross-coupling of organoammonium salts with carboxylic acids was developed. Under the reaction conditions, polyfluoroaromatic carboxylic acids, propiolic acids and α-cyano benzyl carboxylic acid reacted smoothly with benzyl ammonium salts to produce the corresponding carbon-carbon coupling products in good-to-excellent yields.

Decarboxylative Borylation and Cross-Coupling of (Hetero)aryl Acids Enabled by Copper Charge Transfer Catalysis

We report a copper-catalyzed strategy for arylboronic ester synthesis that exploits photoinduced ligand-to-metal charge transfer (LMCT) to convert (hetero)aryl acids into aryl radicals amenable to ambient-temperature borylation. This near-UV process occurs under mild conditions, requires no prefunctionalization of the native acid, and operates broadly across diverse aryl, heteroaryl, and pharmaceutical substrates. We also report a one-pot procedure for decarboxylative cross-coupling that merges catalytic LMCT borylation and palladium-catalyzed Suzuki-Miyaura arylation, vinylation, or alkylation with organobromides to access a range of value-added products. The utility of these protocols is highlighted through the development of a heteroselective double-decarboxylative C(sp²)-C(sp²) coupling sequence, pairing copper-catalyzed LMCT borylation and halogenation processes of two distinct acids (including pharmaceutical substrates) with subsequent Suzuki-Miyaura cross-coupling.

A Palladium-Catalyzed 4CzIPN-Mediated Decarboxylative Acylation Reaction of O-Methyl Ketoximes with α-Keto Acids under Visible Light

This work presents a palladium-catalyzed oxime ether-directed ortho-selective benzoylation using benzoylformic acid as the acyl source with a palladium catalyst and 4CzIPN as the co-catalyst under light. Various non-symmetric benzophenone derivatives were obtained in moderate to good yields. A preliminary mechanism study revealed that the reaction proceeds through a free radical pathway.

Regioselective and late-stage polyfluoroarylation of arenes with diverse fluoroaryl nucleophiles via Pd-catalysis

Dehydrogenative coupling of arenes with fluoroaryl nucleophiles enables the efficient synthesis of fluoroaromatic compounds from readily available starting materials.

Combined Experimental and Computational Mechanistic Investigation of the Palladium-Catalyzed Decarboxylative Cross-Coupling of Sodium Benzoates with Chloroarenes

Reported herein is a mechanistic investigation into the palladium-catalyzed decarboxylative cross-coupling of sodium benzoates and chloroarenes. The reaction was found to be first-order in Pd. A minimal substituent effect was observed with respect to chloroarene, and the reaction was zero-order with respect to chloroarene. Palladium-mediated decarboxylation was assigned as the turnover-limiting step based on an Eyring plot and density functional theory computations. Catalyst performance was found to vary based on the electrophile, which is best explained by catalyst decomposition at Pd(0). The 1,5-cyclooctadiene (COD) ligand contained in the precatalyst CODPd(CH₂TMS)₂ (Pd1) was shown to be a beneficial additive. The bench-stable Buchwald complex XPhosPdG2 could be used with exogenous COD and 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (XPhos) instead of complex Pd1. Adding exogenous XPhos significantly increased the catalyst turnover number and enhanced reproducibility.

Synthesis, characterization, and self-assembly of fluorescent fluorine-containing liquid crystals

S_N Ar has been used to synthesize various functionalized derivatives of pentafluorobenzenes which are highly specific at the para position; and consequently are ideal for building calamitic (rod-like) liquid crystalline molecular systems. Here, we display the effectiveness of S_N Ar chemistry as a convenient method toward the synthesis of fluorescent liquid crystalline perfluorinated comprising ethers and thioethers in excellent yields and high purity. In the current work, we describe the synthesis, self-assembly, and mesogenic properties of new perfluorinated para-terphenyls bearing various para-substituted alkoxy and thioalkoxy chains. The terphenyl core was prepared using Cu(I) (or Cu(I)/phenanthroline)-catalyzed decarboxylative carbon-carbon (or carbon-oxygen [sulfur]) cross-coupling from the analogous aromatic iodide and fluorobenzoate potassium salt. The molecular structures of the prepared perfluorinated terphenyls were demonstrated with ¹ H, ¹³ C, and ¹⁹ F NMR, as well as FT-IR and X-ray crystallography. The liquid crystalline properties and mesogenic phases were characterized with differential scanning calorimetry and high-resolution polarized optical microscope. Both UV-visible absorbance and emission spectra demonstrated solvatochromism. Supramolecular self-assembly of the generated perfluorinated para-terphenyls was monitored by van der Waals and π-π stacking interaction forces. The creation of nanofibrous architectures was monitored by scanning electron microscopy.

Wonderful fusion of organofluorine chemistry and decarboxylation strategy

Decarboxylation strategy has been emerging as a powerful tool for the synthesis of fluorine-containing organic compounds that play important roles in various fields such as pharmaceuticals, agrochemicals, and materials science. Considerable progress in decarboxylation has been made over the past decade towards the construction of diverse valuable fluorinated fine chemicals for which the fluorinated part can be brought in two ways. The first way is described as the reaction of non-fluorinated carboxylic acids (and their derivatives) with fluorinating reagents, as well as fluorine-containing building blocks. The second way is dedicated to the exploration and the use of fluorine-containing carboxylic acids (and their derivatives) in decarboxylative transformations. This review aims to provide a comprehensive summary of the development and applications of decarboxylative radical, nucleophilic and cross-coupling strategies in organofluorine chemistry.

Palladium-catalyzed decarbonylative and decarboxylative cross-coupling of acyl chlorides with potassium perfluorobenzoates affording unsymmetrical biaryls

This paper describes the synthesis of unsymmetrical biaryls by the palladium-catalyzed cross-coupling reaction of acyl chlorides with potassium perfluorobenzoates. This transformation is unique in that it involves simultaneous decarbonylation and decarboxylation under redox-neutral conditions. Compared to conventional cross-coupling protocols for the synthesis of unsymmetrical biaryls, the two reactants in this synthetic strategy can be readily prepared from abundant and inexpensive aromatic carboxylic acids.

Silver-catalyzed decarboxylative radical allylation of α,α-difluoroarylacetic acids for the construction of CF2-allyl bonds

An efficient silver-catalyzed method of decarboxylative radical allylation of α,α-difluoroarylacetic acids to build CF2-allyl bonds has been developed. Using allylsulfone as an allyl donor, α,α-difluorine substituted arylacetic acids bearing various functional groups are successfully allylated to access a series of 3-(α,α-difluorobenzyl)-1-propylene compounds in moderate to excellent yields in aqueous CH3CN solution under the mild conditions. Experimental studies disclosed that the α-fluorine substitution of arylacetic acid has a great influence on free radical activity and reactivity.

Conversions of aryl carboxylic acids into aryl nitriles using multiple types of Cu-mediated decarboxylative cyanation under aerobic conditions

Here, we used malononitrile or AMBN as a cyanating agent to develop efficient and practical protocols for Cu-mediated decarboxylative cyanations, under aerobic conditions, of aryl carboxylic acids bearing nitro and methoxyl substituents at the ortho position as well as of heteroaromatic carboxylic acids. These protocols involved economical methods to synthesize value-added aryl nitriles from simple and inexpensive raw materials. Further diversification of the 2-nitrobenzonitrile product was performed to highlight the practicality of the protocols.

Decarboxylative Cross-Coupling of Acyl Fluorides with Potassium Perfluorobenzoates

We report the transition metal-free decarboxylative cross-coupling reactions of acyl fluorides with potassium perfluorobenzoates. Compared with traditional transition metal-catalyzed cross-couplings, this protocol presents an extremely environmentally benign pathway to afford unsymmetrical diaryl ketones. To install perfluorophenyl groups, this method highlights highly selective, inexpensive, and nontoxic conditions. The reaction system tolerates various functional groups in acyl fluorides. Remarkably, all of the starting materials can be prepared from abundant carboxylic acids and the reaction proceeds without any catalysts and additives.

Gold Catalyzed Decarboxylative Cross-Coupling of Iodoarenes

This report details a decarboxylative cross-coupling of (hetero)aryl carboxylates with iodoarenes in the presence of a gold catalyst (>25 examples, up to 96% yield). This reaction is site specific, which overcomes prior limitations associated with gold catalyzed oxidative coupling reactions. The reactivity of the (hetero)aryl carboxylate correlates qualitatively to the field effect parameter (F_ortho). Reactions with isolated gold complexes and DFT calculations support a mechanism proceeding through oxidative addition at a gold(I) cation with decarboxylation being viable at either a gold(I) or a silver(I) species.

Highly Selective Room-Temperature Suzuki-Miyaura Coupling of Bromo-2-sulfonyloxypyridines for Unsymmetrical Diarylpyridines

A new and mild synthetic approach has been developed for the synthesis of pharmaceutically important unsymmetrical diarylpyridines via chemoselective Suzuki-Miyaura coupling reactions of bromo-2-sulfonyloxypyridines. Most reactions allow for facile access to aryl-2-sulfonyloxypyridines at room temperature in yields of 5-99% with excellent chemoselectivity in the presence of Pd(OAc)₂ (2.0 mol %) and Ad₂BnP (2.4 mol %). The second arylation of the remaining tosyl or triflyl group in the monoarylpyridine derivatives obtained was successfully accomplished for the synthesis of unsymmetrical 2,3-, 2,4-, 2,5-, and 2,6-diarylpyridine derivatives. Furthermore, a one-pot synthesis of unsymmetrical diarylpyridines starting from bromo-2-sulfonyloxypyridine was accomplished to demonstrate the practical convenience. Finally, with this method, an antibacterial agent, a topoisomerase inhibitor, and etoricoxib, a nonsteroidal anti-inflammatory drug, were successfully synthesized from the corresponding bromo-2-hydroxypyridines in overall yields of 80, 86, and 49%, respectively.

Approaching the Integer-Charge Transfer Regime in Molecularly Doped Oligothiophenes by Efficient Decarboxylative Cross-Coupling

A library of symmetrical linear oligothiophene was prepared employing decarboxylative cross-coupling reaction as the key transformation. Thiophene potassium carboxylate salts were used as cross-coupling partners without the need of co-catalyst, base, or additives. This method demonstrates complete chemoselectivity and is a comprehensive greener approach compared to the existing methods. The modularity of this approach is demonstrated with the preparation of discreet oligothiophenes with up to 10 thiophene repeat units. Symmetrical oligothiophenes are prototypical organic semiconductors where their molecular electrical doping as a function of the chain length can be assessed spectroscopically. An oligothiophene critical length for integer charge transfer was observed to be 10 thiophene units, highlighting the potential use of discrete oligothiophenes as doped conduction or injection layers in organic electronics applications.

Selective direct C–H polyfluoroarylation of electron-deficient N-heterocyclic compounds

An efficient protocol of C2-selective direct C–H polyfluoroarylation of six-membered N-heterocyclic compounds with polyfluorobenzoic acid via corresponding N-methyl quaternary ammonium salts.

Palladium-catalyzed salt-free double decarboxylative aryl allylation

We describe a palladium catalyzed salt-free decarboxylative aryl allylation of free benzoic acids with allyl tert-butyl-carbonates.

Palladium-Catalyzed Chemoselective Protodecarboxylation of Polyenoic Acids

Conditions for the first palladium-catalyzed chemoselective protodecarboxylation of polyenoic acids to give the desired polyenes in good yields are presented. The reactions proceed under mild conditions using either a Pd(0) or Pd(II) catalyst and tolerate a variety of aryl and aliphatic substitutions. Unique aspects of the reaction include the requirement of phosphines, water, and a polyene adjacent to the carboxylic acid.

Benzoate Cyclometalation Enables Oxidative Addition of Haloarenes at a Ru(II) Center

The first Ru(II)-catalyzed arylation of substrates without a directing group was recently developed. Remarkably, this process only worked in the presence of a benzoate additive, found to be crucial for the oxidative addition step at Ru(II). However, the exact mode of action of the benzoate was unknown. Herein, we disclose a mechanistic study that elucidates the key role of the benzoate salt in the C–H arylation of fluoroarenes with aryl halides. Through a combination of rationally designed stoichiometric experiments and DFT studies, we demonstrate that the aryl–Ru(II) species arising from initial C–H activation of the fluoroarene undergoes cyclometalation with the benzoate to generate an anionic Ru(II) intermediate. The enhanced lability of this intermediate, coupled with the electron-rich anionic Ru(II) metal center renders the oxidative addition of the aryl halide accessible. The role of an additional (NMe₄)OC(CF₃)₃ additive in facilitating the overall arylation process is also shown to be linked to a shift in the C–H pre-equilibrium associated with benzoate cyclometalation.

Palladium-Catalyzed Direct Arylation of Polyfluoroarenes for Accessing Tetra- ortho-Substituted Biaryls: Buchwald-type Ligand Having Complementary -PPh2 Moiety Exhibits Better Efficiency

The first general examples of direct C-H arylation of electron-deficient polyfluoroarenes with challenging di- ortho-substituted aryl(heteroaryl) chlorides for tetra- ortho-substituted biaryl synthesis are reported. Key to success is the use of Buchwald-type biaryl phosphine ligand, notably with inexpensive -PPh₂ moiety (instead of -PCy₂ group). Pd(OAc)₂ associated with ligand L9 exhibits even higher efficiency than the corresponding SPhos toward this reaction. A wide range of sterically hindered di- ortho-substituted chloroarenes bearing electron-donating or -withdrawing groups are found applicable. Excellent product yields are obtained under mild reaction conditions, and the catalyst loading down to 0.25 mol % of Pd can also be achieved.

Cross-coupling of sulfonic acid derivatives via aryl-radical transfer (ART) using TTMSS or photoredox

The intramolecular cross-coupling of sulfonic acid derivatives occurs in the presence of tris(trimethylsilyl)silane (TTMSS) at room temperature and in air to form biaryl compounds. A photoredox-catalyzed procedure is also described. These protocols provide mild and convenient alternatives to standard tin-mediated reactions.

Decarboxylative formylation of aryl halides with glyoxylic acid by merging organophotoredox with palladium catalysis

Decarboxylative formylation of aryl halides with glyoxylic acid enabled by combining organophotoredox with palladium catalysis.

Palladium-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylic Acids with Aryl Tosylates

Decarboxylative coupling reactions of alkynyl carboxylic acids with aryl tosylates were developed in the presence of a palladium catalyst. Among the commercially available phosphine ligands, only 1-dicyclohexylphosphino-2-(di-tert-butylphosphino-ethyl)ferrocene (CyPF-tBu) showed good reactivity. The reaction took place smoothly and gave the decarboxylative coupled products in moderate to good yields. This demonstrates the excellent functional group tolerance toward alkyl, alkoxy, fluoro, thiophenyl, ester, and ketone groups. In addition, alkyl-substituted propiolic acids, such as octynoic and hexynoic acids, were coupled with phenyl tosylate to provide the desired products. We found that the electronic properties of the substituents on the phenyl ring in arylpropiolic acids are an important factor. The order of reactivity was found to be aryl iodide > aryl bromide > aryl tosylate > aryl chloride. However, aryl chloride-bearing electron-withdrawing groups showed higher reactivity than those bearing aryl tosylates.

Transition-Metal-Free Decarboxylative Iodination: New Routes for Decarboxylative Oxidative Cross-Couplings

Constructing products of high synthetic value from inexpensive and abundant starting materials is of great importance. Aryl iodides are essential building blocks for the synthesis of functional molecules, and efficient methods for their synthesis from chemical feedstocks are highly sought after. Here we report a low-cost decarboxylative iodination that occurs simply from readily available benzoic acids and I₂. The reaction is scalable and the scope and robustness of the reaction is thoroughly examined. Mechanistic studies suggest that this reaction does not proceed via a radical mechanism, which is in contrast to classical Hunsdiecker-type decarboxylative halogenations. In addition, DFT studies allow comparisons to be made between our procedure and current transition-metal-catalyzed decarboxylations. The utility of this procedure is demonstrated in its application to oxidative cross-couplings of aromatics via decarboxylative/C–H or double decarboxylative activations that use I₂ as the terminal oxidant. This strategy allows the preparation of biaryls previously inaccessible via decarboxylative methods and holds other advantages over existing decarboxylative oxidative couplings, as stoichiometric transition metals are avoided.

Visible-Light-Driven Carboxylation of Aryl Halides by the Combined Use of Palladium and Photoredox Catalysts

A highly useful, visible-light-driven carboxylation of aryl bromides and chlorides with CO₂ was realized using a combination of Pd(OAc)₂ as a carboxylation catalyst and Ir(ppy)₂(dtbpy)(PF₆) as a photoredox catalyst. This carboxylation reaction proceeded in high yields under 1 atm of CO₂ with a variety of functionalized aryl bromides and chlorides without the necessity of using stoichiometric metallic reductants.

Highly efficient heterogeneous copper-catalyzed decarboxylative cross-coupling of potassium polyfluorobenzoates with aryl halides leading to polyfluorobiaryls

The decarboxylative cross-coupling of potassium polyfluorobenzoates with aryl halides has been achieved using a recyclable MCM-41-immobilized 1,10-phenanthroline copper(i) complex.

Dual C-F, C-H Functionalization via Photocatalysis: Access to Multifluorinated Biaryls

Multifluorinated biaryls are challenging to synthesize and yet are an important class of molecules. Because of the difficulty associated with selective fluorination, this class of molecules represent a formidable synthetic challenge. An alternative approach to selective fluorination of biaryls is to couple an arene that already possesses C-F bonds in the desired location. This strategy has been regularly utilized and relies heavily on traditional cross-coupling strategies that employ organometallics and halides (or pseudohalides) in order to achieve the coupling. Herein we report conditions for the photocatalytic coupling via direct functionalization of the C-F bond of a perfluoroarene and C-H bond of the other arene to provide an expedient route to multifluorinated biaryls. The mild conditions and good functional group tolerance enable a broad scope, including access to the anti-Minisci product of basic heterocycles. Finally, we demonstrate the value of the C-F functionalization approach by utilizing the high fluorine content to systematically build complex biaryls containing between two and five Caryl-F bonds via the synergistic use of photocatalysis and SNAr chemistry.