Suzuki Coupling of Cyclopropylboronic Acid With Aryl Halides Catalyzed by a Palladium–Tetraphosphine Complex

The tetraphosphine all‐cis‐1,2,3,4‐tetrakis(diphenylphosphinomethyl)cyclopentane (Tedicyp) in combination with [Pd(C₃H₅)Cl]₂ affords a very efficient catalyst for the coupling of cyclopropylboronic acid with aryl bromides and aryl chlorides. Higher reactions rates were observed with aryl bromides than with aryl chlorides; however, even in the presence of 1–0.4% of catalyst, a few aryl chlorides gave the coupling products in good yields. A wide variety of substituents such as alkyl, methoxy, trifluoromethyl, acetyl, benzoyl, formyl, carboxylate, nitro, and nitrile on the aryl halides are tolerated. The coupling reaction of sterically very congested aryl bromides such as bromomesitylene or 2,4,6‐triisopropylbromobenzene also proceeds in good yields.     

Synthesis and applications of a new palladacycle as a high active catalyst in the Suzuki couplings

The reaction of biphenyl-based phosphine P(o-C₆H₄Me)Ph₂ (1) with Pd(OAc)₂ in toluene affords the air and water stable palladacycle (2) as a binuclear compound which has been characterized by multi-nuclear NMR spectroscopy and elemental analysis as a mixture of cis and trans isomers with relative intensity of 1:3, respectively. This palladacycle is a highly efficient catalyst precursor for the coupling of aryl boronic acids and aryl halides. Both activated and deactivated aryl bromides and chlorides are efficiently coupled in the presence of 2 to furnish the corresponding cross-coupled products in excellent yields, and a wide variety of functional groups are tolerated in aryl halides. This methodology has also been extended for the coupling of bromoarylphosphines and bromoarylphosphine oxides with aryl boronic acids for the generation of hindered corresponding products.     

FeCl3/PPh3-catalyzed Sonogashira coupling reaction of aryl iodides with terminal alkynes

Conditions for a FeCl₃/PPh₃-catalyzed and palladium-, copper-, amine free-Sonogashira coupling reaction of aryl halides with terminal alkynes are reported. The protocol was applicable to a wide variety of substituted aryl iodides and alkynes with different steric and electronic properties and gave excellent yields of the desired coupling products.     

trans-Pd(OAc)2(Cy2NH)2 catalyzed Suzuki coupling reactions and its temperature-dependent activities toward aryl bromides

A new catalytic system based on Pd-simple amines for Suzuki coupling reactions of aryl bromides is described. A well-defined air-stable complex, trans-Pd(OAc)₂(Cy₂NH)₂ effectively promotes Suzuki couplings of aryl bromides with a range of aryl boronic acids to give diaryl products in high yields. It also exhibits temperature-dependent activity toward aryl bromides bearing different electronic substituents under reaction conditions.     

Palladaphosphacyclobutenes as catalysts in Heck and Suzuki reactions

Heck reactions of aryl halides with various olefins and Suzuki reactions of aryl halides with phenylboronic acid catalyzed by palladaphosphacyclobutene have been investigated. The scope of the Heck reaction has been investigated in N,N‐dimethylacetamide at 140 °C using NaOAc as base. Using 0.1% molar ratio of palladaphosphacyclobuyenes, aryl bromides were converted into 1,2‐substitutedethene products in good to high yields through coupling with both vinylarenes and acrylates. Actived aryl chloride reacted with styrene to afford 1,2‐substitutedethene products in moderate yields. The scope of the Suzuki reaction has been conducted in toluene at 110 °C using Cs₂CO₃ as base. Using 0.1% molar ratio of palladaphosphacyclobutene, aryl bromides reacted with phenylboronic acid to afford diaryl derivatives in excellent yield. Copyright © 2008 John Wiley & Sons, Ltd.     

Ni-catalyzed cross-coupling reaction of aryl chlorides with arylboronic acids in IPA without using a reducing reagent

The coupling reaction of aryl chlorides with arylboronic acids was successfully performed in isopropanol (IPA) by using [NiCl(Ph₂PCH₂CH₂OH)₂(H₂O)]Cl (5), a cationic Ni(II)-complex, as a precatalyst in the absence of a reducing agent. The coupling reaction proceeded smoothly under mild conditions to provide biaryls in satisfactory to excellent yields, and formation of the undesired dechlorination products of aryl chlorides was completely prevented.     

Gold(I)-catalyzed direct C-H arylation of pyrazine and pyridine with aryl bromides

An efficient procedure for the direct C-H arylation of electron-poor aromatics such as pyrazine and pyridine with aryl bomides is described. In the presence of catalytic amount of Cy₃PAuCl and with the use of t-BuOK as base, pyrazine undergoes the direct C-H arylation with aryl bromides at 100 °C, and the yields of the arylated products depend on the nature of aryl bromides. In the cases of electron-rich aryl bromides used, the arylated pyrazines can be obtained in good to high yields. For electron-poor aryl bromides, the addition of AgBF₄ is the crucial point to accelerate the coupling reaction to give the arylated products in moderate yields. Pyridine also reacts with electron-rich aryl bromides catalyzed by Cy₃PAuCl to give a mixture of arylated regioisomers in moderate yield. However, in order to realize the direct C-H arylation of pyridine with electron-poor aryl bromides, the addition of silver salt as additive and a milder reaction temperature (60 °C) are required.     

Sonogashira coupling reaction of homopropargyl ether with aryl bromides and synthesis of 2,5-disubstituted 3-bromofurans

This paper presents Sonogashira coupling reaction of aryl bromides with protected homopropargyl alcohols such as tert-butyldimethyl(1-phenylbut-3-ynyloxy)silane and tert-butyldimethyl(1-(2,4-dichlorophenyl)but-3-ynyloxy)silane in piperidine catalyzed by PdCl₂/PPh₃ without copper(I). The coupling products, disubstituted acetylene, are obtained in good or excellent yields. These products can be further used for the synthesis of 2,5-disubstituted 3-bromofurans.     

Palladium-catalyzed coupling of vinyl tosylates with arylsulfinate salts

The first palladium-catalyzed coupling of vinyl tosylates with arylsulfinate salts is described. A variety of cyclic and acyclic vinyl tosylates were coupled with aryl sulfinate salts using 2.5 mol % Pd₂(dba)₃/5.0 mol % XantPhos to give vinyl aryl sulfone products in good yields. The coupling was extended to the preparation of a cyclopropyl vinyl sulfone.     

Pd(OAc)2-Catalyzed Carbonylative Coupling of Aryl Iodide with Ortho-Haloamines in Water

The carbonylative cross coupling of aryl iodide with ortho-haloaniline to ortho-haloanilide using phosphine-free Pd(OAc)₂ catalyst in water as a reaction medium has been studied. The present protocol facilitated the reaction of o-haloanilines with a wide variety of hindered and functionalized aryl iodides, affording good yields of the desired products. The protocol was also extended for the synthesis of benzoxazoles through cyclization of ortho-haloanilide using Cu(acac)₂ catalyst.     

Pd-catalyzed coupling of aryl iodides with triarylbismuths as atom-economic multi-coupling organometallic nucleophiles under mild conditions

The facile cross-coupling reactivity of triarylbismuth compounds with aryl iodides was achieved under mild heating conditions. The established catalytic protocol using Pd(OAc)₂(Cy₂NH)₂ system exhibited high coupling reactivity with a variety of triarylbismuth and aryl iodide compounds under mild conditions. These coupling reactions were completed in short reaction time affording good to high yields of functionalized biaryl products. The studies of multi-coupling reactions with tris(4-iodophenyl)amine, 8 also furnished moderate to good yields of coupled products, 8a-8f.     

Palladium-catalysed direct arylations of NH-free pyrrole and N-tosylpyrrole with aryl bromides

The palladium-catalysed direct coupling of aryl halides with pyrroles provides a greener access to arylated pyrroles than more classical couplings such as Suzuki, Stille or Negishi reactions. However, so far, NH-free pyrrole and N-tosylpyrrole gave disappointing results for such couplings either in terms of regioselectivity of the arylation, catalyst loading or substrate scope. The reactivity of both NH-free pyrrole and N-tosylpyrrole was studied, and the tosylated pyrrole led to higher yields of coupling products due to better conversions of the aryl bromides. A range of aryl bromides undergo regioselective coupling at C2 of N-tosylpyrrole in moderate to good yields using 1 mol % [Pd(Cl(C₃H₅)]₂ as the catalyst, KOAc as the base in DMAc.     

CuI-catalyzed direct synthesis of diaryl thioethers from aryl boronic acids and arylsulfonyl chlorides

A CuI-catalyzed direct coupling of aryl boronic acids with arylsulfonyl chlorides for the preparation of diaryl thioethers was developed. The reaction is initiated by a PPh₃ reduction of the arylsulfonyl chloride, followed by a CuI-catalyzed C–S coupling with an aryl boronic acid. Various arylsulfonyl chlorides can directly serve as a sulfur source in this mild and efficient reaction giving the desired products in moderate to good yields. Moreover, this practical method has also been applied to the thioetherification of aryl iodides and acetylacetones.     

Palladium-catalyzed coupling reaction of amino acids (esters) with aryl bromides and chlorides

The bulky and electron-rich MOP type ligands and Pd(dba)₂ combinations showed high efficiency for the coupling reactions of amino acids and inactive aryl halides to give N-aryl amino acids. Under the catalytic conditions, not only α-amino acids, but also β-, γ-, and δ-amino acids have been coupled with aryl chlorides in moderate to high yields; in the case of optically pure β-amino acids as substrates, the optical purities of the coupling products retained.     

In Situ Generation of ArCu from CuF2 Makes Coupling of Bulky Aryl Silanes Feasible and Highly Efficient

A bimetallic system of Pd/CuF₂, catalytic in Pd and stoichiometric in Cu, is very efficient and selective for the coupling of fairly hindered aryl silanes with aryl, anisyl, phenylaldehyde, p‐cyanophenyl, p‐nitrophenyl, or pyridyl iodides of conventional size. The reaction involves the activation of the silane by Cu^II, followed by disproportionation and transmetalation from the Cu^I(aryl) to Pd^II, upon which coupling takes place. Cu^III formed during disproportionation is reduced to Cu^I(aryl) by excess aryl silane, so that the CuF₂ system is fully converted into Cu^I(aryl) and used in the coupling. Moreover, no extra source of fluoride is needed. Interesting size selectivity towards coupling is found in competitive reactions of hindered aryl silanes. Easily accessible [PdCl₂(IDM)(AsPh₃)] (IDM = 1,3‐dimethylimidazol‐2‐ylidene) is by far the best catalyst, and the isolated products are essentially free from As or Pd (<1 ppm). The mechanistic aspects of the process have been experimentally examined and discussed.     

CuI/PPh3‐catalyzed Sonogashira coupling reaction of aryl iodides with terminal alkynes in water in the absence of palladium

The Sonogashira cross‐coupling of aryl iodides with terminal alkynes catalyzed by a simple and inexpensive catalyst system of CuI/PPh₃ in water as the sole solvent has been reported. In the presence of CuI/PPh₃, with KOH used as a base, a number of aryl iodides were treated with alkynes to afford the corresponding products in moderate to excellent yields. Copyright © 2008 John Wiley & Sons, Ltd.     

Decarboxylative C(sp3)−O Cross‐Coupling

Alkyl aryl ethers are an important class of compounds in medicinal and agricultural chemistry. Catalytic C(sp³)?O cross‐coupling of alkyl electrophiles with phenols is an unexplored disconnection strategy to the synthesis of alkyl aryl ethers, with the potential to overcome some of the major limitations of existing methods such as C(sp²)?O cross‐coupling and S_N2 reactions. Reported here is a tandem photoredox and copper catalysis to achieve decarboxylative C(sp³)?O coupling of alkyl N‐hydroxyphthalimide (NHPI) esters with phenols under mild reaction conditions. This method was used to synthesize a diverse set of alkyl aryl ethers using readily available alkyl carboxylic acids, including many natural products and drug molecules. Complementarity in scope and functional‐group tolerance to existing methods was demonstrated.     

Ammonium Chloride Promoted Palladium-Catalyzed UIImann Coupling of Aryl Bromide

In water, ammonium chloride was found to promote palladium-catalyzed Ullmann coupling reactions of aryl bromides. In the presence of Pd/C, zinc, NH4Cl, and water, coupling of various aryl bromides was carried out smoothly to afford the corresponding homocoupling products in moderate yields.     

Metal-free synthesis of aryl esters by coupling aryl carboxylic acids and aryl boronic acids

A facile synthesis of aryl esters is developed by coupling aryl carboxylic acids and aryl boronic acids in the presence of PhI(OAc)₂ and carbonyl diimidazole. A wide range of functional groups were tolerant to the metal-free reaction condition that led to the desired products in good yields.     

Palladium supported on zinc ferrite: an efficient catalyst for ligand free C–C and C–O cross coupling reactions

An efficient superparamagnetic Pd–ZnFe₂O₄ solid catalyst has been synthesized by loading Pd(0) species on zinc ferrite nanoparticles. Sonogashira cross couplings between terminal alkynes and aryl halides were achieved in the absence of any Cu co-catalyst. A Heck–Matsuda coupling reaction of structurally different aryldiazonium tetrafluoroborate substrates was preceded at 40 °C in water. Cyanation of aryl halides was successfully done using K₄[Fe(CN)₆] as the cyanide source over Pd–ZnFe₂O₄. The catalyst was also employed for Ullmann type cross coupling reactions. Excellent yield of the products, reusability, and uncomplicated work-up make this catalyst efficient for C–C and C–O coupling reactions. Good yield of products, easy separation, and negligible leaching of Pd from the catalyst surface confirm the true heterogeneity in these catalytic reactions.