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.     

Synthesis and properties of z-1,3-bis-(aryl)-4-bromo-2-buten-1-ones

Bromination of 1,3-bis(aryl)-2-buten-1-ones by N-bromosuccinimide in anhydrous carbon tetrachloride gives Z-1,3-bis(aryl)-4-bromo-2-buten-1-ones. The effect of the nature of substituent in the benzene ring on the course of a reaction with nucleophiles has been studied. Heating an alcohol solution of these ketones (Ar = 4-MeOC₆H₄, 4-ClC₆H₄) in the presence of acid or in the presence of base (Ar = Ph) gave 2,4-bis(aryl)furans. Treatment of 1,3-bis(aryl)-4-bromo-2-buten-1-ones with thioacetamide gave 2,4-bis(aryl)thiophenes. The oxidation of the halo-substituted dypnones with H₂O₂/NaOH gave (3-bromomethyl-3-aryl-2-oxiranyl)(aryl)methanones. The reaction of halo-substituted dypnones with aryl hydrazines gave 1,3,5-triaryl-1,6-dihydropyridazines or 1,3,5-triarylpyridazinium bromides depending on the structure of the reagents.     

Palladium‐catalyzed cyanation reaction of aryl halides using K4[Fe(CN)6] as non‐toxic source of cyanide under microwave irradiation

An efficient method for preparation of aryl nitriles—using [Pd{C₆H₂(CH₂CH₂ NH₂)‐(OMe)₂,3,4} (µ‐Br)]₂ complex as an efficient catalyst and K₄[Fe(CN)₆] as a green cyanide source—from aryl bromides, aryl iodides and aryl chlorides under microwave irradiation has been reported. This complex has been demonstrated to be an active and efficient catalyst for this reaction. Using a catalytic amount of this synthesized palladium complex in DMF at 130 °C led to production of the cyanoarenes in excellent yields in short reaction times. Copyright © 2010 John Wiley & Sons, Ltd.     

Highly efficient orthopalladated complexes of second and third benzyl amine for catalyzing the Suzuki cross‐coupling reaction

In this work, ortho‐palladated complexes [Pd(µ‐Cl)(C₆H₄CH₂ NRR′‐κ²‐C,N)]₂ and [Pd(C₆H₄CH₂NH₂‐2‐C,N)Cl(Y)] were tested in the Suzuki–Miyaura cross‐coupling reaction. Cyclopalladated Pd(II) complexes as thermally stable catalysts can activate aryl bromides and chlorides. These complexes were active and efficient catalysts for the Suzuki–Miyaura reaction of aryl bromides and even less reactive aryl chlorides. The cross‐coupled products of a variety of aryl bromides and aryl chloride with phenylboronic acid in methanol as solvent at 60 °C were produced in excellent yields. Copyright © 2010 John Wiley & Sons, Ltd.     

Oxidative addition of aryl chlorides to palladium N-heterocyclic carbene complexes and their role in catalytic arylamination

Density functional theory has been used to investigate various solvated species that may be formed from palladium bis N-heterocyclic carbene complexes, [Pd(cyclo-C{NRCH}₂)₂], (PdL₂) in benzene solution. Formation of an η²-arene complex is shown to stabilise a monocarbene species, PdL(η²-C₆H₅X), where the arene is either the solvent or a reacting aryl halide. Oxidative addition of an aryl chloride has been modelled, and the most likely transition state has been established as a PdL(arylchloride) species, with just one carbene ligand coordinated to the palladium. The catalytic cycle for aryl amination has been investigated and the oxidative addition of the aryl halide shown to be the rate determining step. Reductive elimination of the aryl amine has a lower activation energy. Oxidative addition of alkyl halides has been shown to be less favourable because of the absence of an unsaturated group, such as the aryl ring, to bond to the palladium.     

Synthesis of Alkyl-Aryl Ethers by Copper-catalyzed Etherization Reactions of Aryl Fluorides with Tetraalkylammonium Bromides and H2O

Synthesis of alkyl aryl ethers via copper‐catalyzed etherizations of electron‐deficient aryl fluorides with quaternary ammonium bromides and water has been developed. In the presence of Cu(OAc)₂, POPh₃ ( L4 ) and Cs₂CO₃, a variety of electron‐deficient aryl fluorides underwent the reaction with quaternary ammonium bromides and H₂O in moderate to good yields. The mechanism was also discussed.     

One-pot synthesis of monosubstituted aryl(hetaryl)acetylenes by direct introduction of the CCH residue into arenes and hetarenes

A convenient one-pot synthesis of aryl(hetaryl)acetylenes by cross-coupling of aryl(hetaryl)iodides with acetylene in presence of PdCl₂(Ph₃)₂, CuI and K₂CO₃ in DMF has been developed.     

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.     

A facile microwave-assisted palladium-catalyzed cyanation of aryl chlorides

We report an efficient method for the preparation of aryl nitriles from aryl chlorides under either microwave assisted or thermal conditions. A catalyst system comprising tris(dibenzylidene acetone)dipalladium (Pd₂(dba)₃) and 2-(2′,6′-dimethoxybiphenyl)dicyclohexylphosphine (S-Phos) is shown to effectively promote cyanation of various aryl chlorides with Zn(CN)₂ as the cyanide source.     

Preparation of Complexes of Nickel(II) Aryl Carboxylates with Morpholine and Piperidine

Complexes of nickel(II) aryl carboxylates with a general formula Ni(RC₆H₄COO)₂L₂ where R=H, p-CH₃. p-Cl, m- & p-NO₂; and L = morpholine and piperidine; have been prepared by the interaction of nickel(II) aryl carboxylates with a large excess of appropriate amine. Unlike parent anhydrous nickel(II) aryl carboxylates all these complexes are soluble in common organic solvents.     

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.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

Polyfluoroorganoboron‐Oxygen Compounds. 1 Polyfluorinated Aryl(dihydroxy)boranes and Tri(aryl)boroxins

A general preparative procedure for polyfluorinated aryl(dihydroxy)boranes C₆H_5‐nF_nB(OH)₂ (n = 3 — 5) is described. Polyfluorinated aryl(dihydroxy)boranes are easily dehydrated to the corresponding tri(aryl)boroxins (C₆H_5‐nF_nBO)₃ by thermal or chemical treatment. The property of the acids C₆H_5‐nF_nB(OH)₂ to condensate depends on the number and on the position of the fluorine atoms in the aryl group. Examples of both classes of boron compounds were isolated as pure individuals and characterized by multinuclear NMR spectroscopy.     

Unexpected regioselectivity in the palladium‐catalyzed reaction of silacyclobutanes with aryl iodides

The reaction of aryl iodides with 1,1‐diphenyl‐silacyclobutane in the presence of a catalytic amount of Pd(PPh₃)₄ affords unexpected ring‐opening adducts, 1‐ and 2‐propenyl(triaryl)‐silanes, in good yields. On the other hand, the PdCl₂(PhCN)₂‐catalyzed reaction of 1,1‐diphenylsilacyclobutanes with aryl halides gives ­unexpected products, triarylsilanols, after ­hydrolysis in moderate yields. The catalysis involves the reaction of aryl–palladium intermediates with silacyclobutanes along with ­regioselective aryl–silicon bond formation. Copyright © 2001 John Wiley & Sons, Ltd.     

Three‐Step Synthesis of 3‐Aryl‐2‐sulfanylthieno[2,3‐b]‐, ‐[2,3‐c]‐, or ‐[3,2‐c]pyridines from the Corresponding Aryl(halopyridinyl)methanones

A convenient three‐step procedure for the synthesis of three types of 3‐aryl‐2‐sulfanylthienopyridines 4, 8 , and 12 has been developed. The first step of the synthesis of thieno[2,3‐b]pyridine derivatives 4 is the replacement of the halo with a (sulfanylmethyl)sulfanyl group in aryl(2‐halopyridin‐3‐yl)methanones 1 by successive treatment with Na₂S?9 H₂O and chloromethyl sulfides to give aryl{2‐[(sulfanylmethyl)sulfanyl]pyridin‐3‐yl}methanones 2 . In the second step, these were treated with LDA (LiNⁱPr₂) to give 3‐aryl‐2,3‐dihydro‐2‐sulfanylthieno[2,3‐b]pyridin‐3‐ols 3 , which were dehydrated in the last step with SOCl₂ in the presence of pyridine to give the desired products. Similarly, thieno[2,3‐c]pyridine and thieno[3,2‐c]pyridine derivatives, 8 and 12 , respectively, can be prepared from aryl(3‐chloropyridin‐4‐yl)methanones 5 and aryl(4‐chloropyridin‐3‐yl)methanones 9 , respectively.     

An Efficient and General Method for Formylation of Aryl Bromides with CO2 and Poly(methylhydrosiloxane)

The formylation of aryl halides with CO₂ to generate aryl aldehydes is challenging. Herein, we report a novel synthesis of aryl aldehydes by formylation of aryl bromides with CO₂ and a waste silane, poly(methylhydrosiloxane) (PMHS). It has been discovered that a simple combination of 1,3‐bis(diphenyphosphino)propane (DPPP)‐chelated Pd catalyst, Pd(DPPP)Cl₂, with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) is able to effectively catalyze the reaction, leading to aryl aldehydes in moderate to excellent yields, and without any by‐products in most cases. Moreover, this route could be extended to the formylation of aryl iodides with high efficiency. This approach is simple, less costly, and environmentally friendly, and also widens the applications of CO₂ to form value‐added chemicals by the construction of new C?C bonds.     

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.     

A practical synthesis of highly functionalized aryl nitriles through cyanation of aryl bromides employing heterogeneous Pd/C

An industrially viable cyanation of aryl bromides with Zn(CN)₂ was accomplished in the presence of inexpensive and readily accessible Pd/C, Zn dust, ZnBr₂, and PPh₃ in DMA to provide functionalized aryl nitriles in moderate to high yields.     

On the catalytic duo PdCl2(PPh3)2/AuCl(PPh3) that cannot effect a Sonogashira-type reaction: a correction

In contrast to the observation made by the Laguna group, we report that the combination of PdCl₂(PPh₃)₂ and AuCl(PPh₃) makes a unique catalytic system that allows Sonogashira-type cross-coupling of both aryl and alkyl alkynes with aryl halides in excellent yields.     

Cyclization–oxidation of Benzylidenehydrazinecarbothioamides by FeCl3.6H2O or ZnCl2.6H2O Catalysts and Synthesis of New 1,3,4‐Thiadiazolo‐[3,2‐ α]Pyrimidines

We report new method for preparation of 2‐amino‐5‐aryl‐1,3,4‐thiadiazoles by reaction of arylaldehyde with thiosemicarbazide and in the next step via cyclization of 2‐aryl hydrazinecarbothioamide in the presence of ZnCl₂.6H₂O or FeCl₃.6H₂O. Also, in this research, new substituted 1,3,4‐thiadiazolo‐[3,2‐α]pyrimidines were synthesized by the reaction of 2‐amino‐5‐aryl‐1,3,4‐thiadiazoles derivatives with DMAD or DEAD in the presence of K₂CO₃ under reflux conditions. The FT‐IR, ¹H‐NMR, ¹³C‐NMR, elemental analysis and single‐ crystal X‐ray analysis confirm the structures of the products.