A versatile method for the synthesis of diaryl and alkyl aryl ketones via palladium‐catalysed cross‐coupling reaction of arylboronic acids with acyl chlorides

An efficient catalytic system using 1‐benzyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane chloride and PdCl₂ was developed for the cross‐coupling reaction of arylboronic acids with acyl chlorides. The catalytic amount of this homogeneous catalytic system affords the corresponding diaryl and alkyl aryl ketones in good to excellent yields under mild reaction conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Imidazole‐coordinated monodentate NHC–Pd(II) complex derived from proline and its application to the coupling reaction of arylboronic acids with carboxylic acid anhydrides in water at room temperature

Cleavage of a C N bond of imidazolium salt derived from N‐phenyl‐substituted proline was observed in this laboratory. A novel imidazole‐coordinated monodentate NHC–Pd(II) complex 5 was obtained as the sole product in good yield in the reaction of imidazolium salt 4 with Pd(OAc)₂ in refluxing THF. The structure of complex 5 was determined unambiguously by an X‐ray diffraction. The complex was found to be a good catalyst in the cross‐coupling reaction of arylboronic acids with carboxylic acid anhydrides in water at room temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

Palladium‐catalysed Suzuki cross‐coupling of primary alkylboronic acids with alkenyl halides

The Suzuki reaction of primary alkylboronic acids with alkenyl halides proceeds nicely using the air‐stable catalyst PdCl(C₃H₅)(dppb), Cs₂CO₃ as base and toluene or xylene as solvent. A minor effect of the substituent position of the alkenyl bromide was observed. Quite similar yields were observed in the presence of α‐ or β‐substituted alkenyl bromides such as 2‐bromobut‐1‐ene or 1‐bromo‐2‐methylprop‐1‐ene with this catalyst. This reaction proceeded with a variety of alkylboronic acids such as 2‐phenylethylboronic acid or n‐octylboronic acid. Lower yields of coupling products were obtained in the presence of an alkenyl chloride. Copyright © 2008 John Wiley & Sons, Ltd.     

(N‐heterocyclic carbene)PdCl(N‐heterocyclic carboxylate) complexes: Synthesis and catalytic activities towards arylation of benzoxazoles with aryl halides

A series of N‐heterocyclic carboxylate‐stabilized N‐heterocyclic carbene palladium complexes have been synthesized and fully characterized. The solid‐state structures indicate that each of the palladium centers is coordinated by an N‐heterocyclic carbene, a chloride and a bidentate N,O‐donor N‐heterocyclic carboxylate ligand. The catalytic performance of the complexes was screened and the results revealed that the complexes exhibit moderate to high catalytic activities for the direct C─H bond arylation of benzoxazoles with aryl bromides.     

Polystyrene‐supported Pd(II)–N‐heterocyclic carbene complex as a heterogeneous and recyclable precatalyst for cross‐coupling of acyl chlorides with arylboronic acids

Palladium‐catalysed cross‐coupling reaction of aroyl chlorides with arylboronic acids was achieved in the presence of polystyrene‐supported palladium(II)–N‐heterocyclic carbene complex, using K₂CO₃ in acetone–water, providing diaryl ketones in high yields. Furthermore, the heterogeneous catalyst could be reused up to four times without significant loss of activity.     

The Suzuki cross‐coupling reaction in pure water catalyzed by ligandless palladium using polyethylene glycol derivatives as surfactant

The results of a ligandless Pd(OAc)₂‐catalyzed Suzuki–Miyaura coupling experiment are presented. It was found that the use of polyethylene glycol phosphonium salts (PEG‐quat) as surfactant resulted in very rapid reactions of aryl halides with phenylboronic acids in pure water. Moreover, aryl chlorides such as 4‐nitrochlorobenezene reacted quantitatively with phenylboronic acid under optimized conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Highly efficient N‐Heterocyclic carbene–palladium complex‐catalyzed multicomponent carbonylative Suzuki reaction: novel practical synthesis of unsymmetric aryl ketones

Highly efficient and chemoselective N‐heterocyclic carbene palladium complexes‐catalyzed multicomponent carbonyltive Suzuki reaction with sodium tetraphenylborate used as phenylating reagent has been demonstrated in this article. Both electron‐rich and electron‐deficient aryl iodides gave unsymmetric aryl ketones in excellent yields. Copyright © 2007 John Wiley & Sons, Ltd.     

Palladium‐catalyzed decarboxylative coupling of α,β‐unsaturated carboxylic acids with aryl tosylates

We report a general method for selective cross‐coupling of α,β‐unsaturated carboxylic acids with aryl tosylates enabled by versatile Pd(II) complexes. This method features the general cross‐coupling of ubiquitous α,β‐unsaturated carboxylic acids by decarboxylation. The transformation is characterized by its operational simplicity, the use of inexpensive, air‐stable Pd(II) catalysts, scalability and wide substrate scope. The reaction proceeds with high trans selectivity to furnish valuable (E)‐1,2‐diarylethenes.     

Pd‐Catalyzed Decarboxylative Cross‐Coupling of 2‐Carboxyazine N‐Oxides with Various (Hetero)aryl Halides

Decarboxylative cross‐coupling reactions of substituted 2‐carboxyazine N‐oxides, with a variety of (hetero)aryl halides, by bimetallic Pd⁰/Cu^I and Pd⁰/Ag^I catalysis are reported. Two possible pathways, a conventional bimetallic‐catalyzed decarboxylative arylation, as well as a protodecarboxylative/direct C?H arylation sequence have been considered. These methods provide the first general decarboxylative arylation methodology for the 2‐carboxyazine series.     

A Suzuki‐type cross‐coupling reaction of arylacetylene halides with arylboronic acids

A PdCl₂‐catalyzed direct alkynylation of arylboronic acids to give diarylacetylenes is described. The optimal conditions using PdCl₂ as catalyst, MeOH PhMe H₂O as solvent and K₂CO₃ as base effectively suppressed the formation of homo‐coupling product and afforded moderate to good yield of the desired unsymmetrical coupling product. This reaction represents a Suzuki‐type sp²(C B)–sp(C X) cross‐coupling. Copyright © 2011 John Wiley & Sons, Ltd.     

A Novel Metal‐free Reductive Esterification of N‐Tosylhydrazones with Carboxylic Acids

A novel method for the synthesis of esters via reductive coupling of N‐tosylhydrazones with carboxylic acids under metal‐free conditions has been developed. Various functional groups were found to be tolerable under the reaction conditions to afford low to good yields.     

Biaryl and Aryl Ketone Synthesis via Pd‐Catalyzed Decarboxylative Coupling of Carboxylate Salts with Aryl Triflates

A bimetallic catalyst system has been developed that for the first time allows the decarboxylative cross‐coupling of aryl and acyl carboxylates with aryl triflates. In contrast to aryl halides, these electrophiles give rise to non‐coordinating anions as byproducts, which do not interfere with the decarboxylation step that leads to the generation of the carbon nucleophilic cross‐coupling partner. As a result, the scope of carboxylate substrates usable in this transformation was extended from ortho‐substituted or otherwise activated derivatives to a broad range of ortho‐, meta‐, and para‐substituted aromatic carboxylates. Two alternative protocols have been optimized, one involving heating the substrates in the presence of Cu^I/1,10‐phenanthroline (10–15 mol %) and PdI₂/phosphine (2–3 mol %) in NMP for 1–24 h, the other involving Cu^I/1,10‐phenanthroline (6–15 mol %) and PdBr₂/Tol‐BINAP (2 mol %) in NMP using microwave heating for 5–10 min. While most products are accessible using standard heating, the use of microwave irradiation was found to be beneficial especially for the conversion of non‐activated carboxylates with functionalized aryl triflates. The synthetic utility of the transformation is demonstrated with 48 examples showing the scope and limitations of both protocols. In mechanistic studies, the special role of microwave irradiation is elucidated, and further perspectives of decarboxylative cross‐couplings are discussed.     

Palladium‐Catalyzed Aminocarbonylation of N‐Chloroamines with Boronic Acids

Aryl (pseudo)halide‐based (C?X) carbonylation reactions have been extensively studied during the past few decades. From both academic and synthetic points of view, the carbonylative transformation of N?X bonds represents an interesting and attractive area of investigation. In light of this, the first carbonylative cross‐coupling between N‐chloroamines and organoboronic acids has been developed. This new type of aminocarbonylation proceeds at mild temperatures (45–55 °C) with 2 mol % Pd/C (10 wt %) as the ligand‐free catalyst. Not only arylboronic acids, but also alkenyl‐ and alkylboronic acids can be applied as the substrates and bromide and iodide substituents in the substrates are well tolerated. Initial mechanistic investigations have also been performed.     

Synthesis of novel palladium N‐heterocyclic‐carbene complexes as catalysts for Heck and Suzuki cross‐coupling reactions

Novel palladium‐1,3‐dialkylperhydrobenzimidazolin‐2‐ylidene (2a–c) and palladium‐1,3‐dialkylimidazolin‐2‐ylidene complexes (4a,b) have been prepared and characterized by C, H, N analysis, ¹H‐NMR and ¹³C‐NMR. Styrene or phenylboronic acid reacts with aryl halide derivatives in the presence of catalytic amounts of the new palladium‐carbene complexes, PdCl₂(1,3‐dialkylperhydrobenzimidazolin‐2‐ylidene) or PdCl₂(1,3‐dialkylimidazolin‐2‐ylidene) to give the corresponding C? C coupling products in good yields. Copyright © 2006 John Wiley & Sons, Ltd.     

N‐Heterocyclic carbene/phosphite synergistically assisted Pd/C‐catalyzed Suzuki coupling of aryl chlorides

An N‐heterocyclic carbene and phosphite synergistically enhanced Pd/C catalyst system has been developed for Suzuki coupling of aryl chlorides and aryl boronic acids from commercially available Pd/C with sterically demanding N,N′‐bis(2,6‐diisopropylphenyl)imidazolylidene and trimethylphosphite. A remarkable increase in catalytic activity of Pd/C was observed when used along with 1 equiv. N,N′‐bis(2,6‐diisopropylphenyl)imidazolium chloride and 2 equiv. phosphite with respect to palladium in appropriate solvents that were found to play a crucial role in Pd/C‐NHC‐P(OR)₃‐catalyzed Suzuki coupling. A dramatic ortho‐substitution effect of carbonyl and nitrile groups in aryl chlorides was observed and explained by a modified quasi‐heterogeneous catalysis mechanism. The Pd/C catalyst could be easily recovered from reaction mixtures by simple filtration and only low palladium contamination was detected in the biparyl products. A practical process for the synthesis of 4‐biphenylcarbonitrile has therefore been developed using the N‐heterocyclic carbene/phosphite‐assisted Pd/C‐catalyzed Suzuki coupling. Copyright © 2013 John Wiley & Sons, Ltd.     

Electroinduced oxidative copolymerization of N‐vinyl carbazole with methyl ethyl ketone formaldehyde resin

In this study, a novel procedure to obtain the non‐crosslinked, photoconductive, white form of the linear copolymer of N‐vinyl carbazole (NVCz) and methyl ethyl ketone formaldehyde resin (MEKF‐R) is reported. A possible mechanism of copolymerization is suggested. The yield of the copolymer is increased almost 10 times by the addition of catalytic amounts of ceric ammonium nitrate as an oxidant during the electrochemical polymerization of NVCz in the presence of MEKF‐R in a divided electrochemical cell. Since cerium(III) is readily oxidized to cerium(IV) at the anode, the concentration of cerium(IV) remained constant and the deposition of green poly(NVCz) can be prevented. Copyright © 2004 John Wiley & Sons, Ltd.     

Palladium‐catalyzed carbonylative cyclization of β‐bromo‐α,β‐unsaturated carboxylic acids with primary amines leading to N‐alkylmaleimides

Cyclic β‐bromo‐α,β‐unsaturated carboxylic acids are carbonylatively cyclized with primary amines under carbon monoxide pressure in MeCN in the presence of a catalytic amount of PdCl₂(PPh₃)₂ to give N‐alkylmaleimides. Copyright © 2012 John Wiley & Sons, Ltd.     

The thermoregulated ligand–palladium‐catalyzed carbonylative Sonogashira coupling of aryl iodides with terminal alkynes in water

The carbonylative Sonogashira coupling of aryl iodides with terminal alkynes was studied by using thermoregulated ligand–palladium as an efficient and reusable catalyst at 80 °C in water. The corresponding alkynone products were obtained in good to excellent yields under 1 atm of carbon monoxide. The isolation of the products was readily achieved by extraction with ethyl acetate, and the catalyst recovered in water can be reused and recycled up to four times without significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

A study into Stille cross‐coupling reaction mediated by palladium catalysts deposited over siliceous supports bearing N‐donor groups at the surface

Mesoporous molecular sieve SBA‐15 and conventional silica gel were grafted with 3‐[2‐(diethylamino)ethylamino]propyl groups and used as supports for the preparation of deposited palladium catalysts, which were subsequently evaluated in Stille cross‐coupling reaction of aryl bromides. The highest conversions were achieved with the metal‐saturated catalyst resulting from the modified SBA‐15. Influence of various reaction parameters (solvent, additive, temperature, etc.) on the overall yield and selectivity was studied. Copyright © 2013 John Wiley & Sons, Ltd.     

A convenient and practical heterogeneous palladium‐catalyzed carbonylative Suzuki coupling of aryl iodides with formic acid as carbon monoxide source

A practical heterogeneous palladium‐catalyzed carbonylative Suzuki coupling of aryl iodides with arylboronic acids under carbon monoxide gas‐free conditions has been developed using a bidentate phosphino‐functionalized magnetic nanoparticle‐immobilized palladium(II) complex as catalyst. Formic acid was utilized as the carbon monoxide source with dicyclohexylcarbodiimide as the activator, and a wide variety of biaryl ketones were generated in moderate to high yields. The new heterogeneous palladium catalyst can be prepared via a simple procedure and can easily be separated from a reaction mixture by simply applying an external magnet and recycled up to 10 times without any loss of activity.