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.     

Tetraphosphine/palladium catalysed Suzuki cross-coupling reactions of aryl halides with alkylboronic acids

Through the use of [PdCl(C₃H₅)]₂/cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as a catalyst, a range of aryl bromides and chlorides undergoes Suzuki cross-coupling with alkylboronic acids in good yields. Several alkyl substituents such as ethyl, n-butyl, n-octyl, isobutyl or 2,2-dimethylpropyl on the alkylboronic acids have been successfully used. The functional group tolerance on the aryl halide is remarkable; substituents such as fluoro, methyl, methoxy, acetyl, formyl, benzoyl, nitro or nitrile are tolerated. Furthermore, this catalyst can be used at low loading, even for reactions of sterically hindered aryl bromides.     

N-picolinamides as ligands for Ullmann-type homocoupling reactions

The use of N-phenylpicolinamide (NPPA) as a ligand in Ullmann-type homocoupling reactions of aryl iodides and bromides in common solvents, such as DMF and MeCN has been successfully demonstrated at room temperature. In addition, this work provided the first example of the homocoupling of an aryl chloride at 82 °C, which is a relatively low temperature when compared to regular Ullmann reaction temperatures. Also, NPPA was successfully employed in base—and heat free Suzuki reactions, including electron rich and poor aryl halides with heteroarylboronic acids in moderate yields.     

Direct synthesis of 3-arylpropionic acids by tetraphosphine/palladium catalysed Heck reactions of aryl halides with acrolein ethylene acetal

Through the use of [PdCl(C₃H₅)]₂/Cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as a catalyst, a range of aryl bromides undergoes Heck reaction with acrolein ethylene acetal. With this acetal, the selective formation of 3-arylpropionic acids/esters was observed. The functional group tolerance on the aryl halide is remarkable; substituents such as fluoro, methyl, methoxy, acetyl, formyl, benzoyl, nitro or nitrile are tolerated. Furthermore, this catalyst can be used at low loading, even for reactions of sterically hindered aryl bromides.     

Heck cross-coupling of vinyl heteroaromatic compounds with aryl and heteroaryl halides using Pd(II) complex under phosphine-free conditions

The palladium-catalyzed cross-coupling reaction of vinyl heteroaromatic compounds with aryl bromides and heteroaryl bromides is described using air and moisture stable N,N′,N″,O-tetrafunctional Pd catalyst under phosphine-free conditions. As a result a variety of trans-1,2-disubstituted vinyl heterocycles were obtained in high to good yields.     

Palladium-catalyzed arylation of vinylic acetates. Phosphine ligand influenced regioselectivity

A palladium-catalyzed coupling reaction of aryl bromides with vinylic acetates in the presence of tributyltin methoxide has been described. The α-arylation aldehyde product and the aryl ketone were obtained in the presence of P(t-Bu)₃ and P(o-Tol)₃, respectively.     

Palladium(II)-N-heterocyclic carbene complex derived from proline towards Suzuki-Miyaura coupling reaction in water at room temperature

Palladium(II)-N-heterocyclic carbene complex 1 derived from proline has been proved to be a highly effective catalyst in the Suzuki-Miyaura coupling reaction of aryl iodides and bromides with arylboronic acids in water at room temperature. The reactions are tolerant towards various functional groups in the substrates. Moreover, the complex 1-catalyzed medium-scale (10.0 mmol) Suzuki-Miyaura reactions were also carried out and it was found that the complex was also effective enough in these cases.     

A palladium complex with a new hemilabile amino- and sulfur-containing phosphinite ligand as an efficient catalyst for the Heck reaction of aryl bromides with styrene. The effect of the amino group

A palladium complex with a new hemilabile amino- and sulfur-containing phosphinite ligand has been synthesised and its crystal structure determined. This system efficiently catalyses the Heck reaction of aryl bromides with styrene at 130°C after 24 h, with turnover numbers of up to 100000 and with a selectivity towards trans-stilbenes ranging from 91.5 to 96.3%. The analogous sulfur-containing phosphinite without the amino group has also been synthesised and subjected to the Heck reaction. The constructive role of the amino group on the formation of the P,S-chelate palladium complex as well as in the Heck reaction is discussed.     

Desulfinative palladium‐catalyzed cross‐coupling of arylsulfonyl hydrazides with aryl bromides under air

A highly efficient and mild palladium‐catalyzed cross‐coupling of arylsulfonyl hydrazides and aryl bromides for the selective synthesis of unsymmetrical biaryls has been developed. This methodology has the advantages of easily accessible starting materials, functional group tolerance and a wide range of substrates, which provide rapid access to biaryls derivatives. In this protocol, abundant and stable aryl bromides serve as the aryl sources by coupling reaction of the aryl group generated from arylsulfonyl hydrazides via in situ release of nitrogen and sulfur dioxide. No external oxidants or acids are needed for this kind of transformation.     

O-Aryloxime ether analogues as novel and efficient ligands for palladium-catalyzed Suzuki–Miyaura coupling in water

O-Aryloxime ether analogues L1–L3 were studied as ligands in palladium-catalyzed Suzuki–Miyaura cross-coupling reaction of aryl bromides and aryl boronic acids in water at room temperature. Reaction conditions for the cross-coupling were optimized using PdCl₂ and Pd(OAc)₂ under aerobic condition. From the three electronically diverse O-aryloxime ether ligands studied herein, the use of 1-phenyl-ethanone O-(4-chloro-phenyl)-oximeL2 exhibits the best catalytic system in the presence of K₂CO₃ as the base and TBAB as the promoter.     

Highly effective activation of aryl chlorides for Suzuki coupling in aqueous media using a ferrocene-based Pd(II)–diimine catalyst

The Suzuki coupling of aryl chlorides with boronic acids using a ferrocene-containing Pd(II)–diimine complex as catalyst, in aqueous media, under microwave heating is reported. A small amount of the catalyst (0.1%) was found to be highly effective for coupling unactivated aryl chlorides with boronic acids to form sterically hindered ortho-substituted biaryls. The same catalyst also enabled the coupling of aryl bromides and iodides with various boronic acids in very high yields. The catalyst is air stable and the catalytic reaction can be completed in 15 min.     

Copper-catalyzed aryl amination in aqueous media with 2-dimethylaminoethanol ligand

Copper-catalyzed amination of aryl bromides and iodides under mild conditions has been developed with 2-dimethylaminoethanol as ligand and water as solvent. A variety of hydrophilic and hydrophobic aryl halide substrates have been aminated in good yield with a variety of amino acids, amino alcohols and peptides. This method has successfully N-arylated some hydrophilic amino compounds not available by other methods.     

Simple amine/Pd(OAc)(2)-catalyzed suzuki coupling reactions of aryl bromides under mild aerobic conditions

A new palladium catalyst (DAPCy) made from Pd(OAc)(2) and commercially available, inexpensive dicyclohexylamine has been developed for the Suzuki coupling reaction of aryl bromides with boronic acids to give the coupling products in good to high yields. The air-stable catalyst was characterized and well-defined by X-ray crystallography. A catalytic system involving DAPCy in dioxane demonstrates a temperature-dependent reactivity toward aryl bromides with different electronic substituents, and selectively couples electron-deficient aryl bromides with boronic acids over electron-rich ones at room temperature. Another catalytic system employing DAPCy in EtOH provides a general and convenient method to prepare biaryls from aryl bromides and boronic acids with a broad range of functional groups at room temperature and under aerobic conditions.     

Heck reactions of 2-substituted enol ethers with aryl bromides catalysed by a tetraphosphine/palladium complex

cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ efficiently catalyses the Heck reaction of β-substituted enol ethers with aryl bromides. Employing β-methoxystyrene, 3-ethoxyacrylonitrile or methyl 3-methoxyacrylate, the regioselective α-arylation of these enol ethers was observed in all cases, and mixtures of Z and E isomers were generally obtained, which in many cases yielded a single ketone product after acid treatment. The stereoselectivity of this reaction depends on steric and electronic factors, and better stereoselectivities in favour of Z isomers were observed with electron-rich or sterically congested aryl bromides. Better yields were obtained for this reaction with electron-rich or sterically congested aryl bromides than with electron-poor aryl bromides. This observation suggests that with these β-substituted enol ethers the rate-limiting step of the catalytic cycle is not the oxidative addition of the aryl bromide to the palladium complex.     

Efficient indoles and anilines syntheses employing tert-butyl sulfinamide as ammonia surrogate

tert-Butyl sulfinamide is an ammonia equivalent for the palladium-catalyzed amination of aryl bromides and aryl chlorides. Using these amine derivatives, it has been observed that indoles and anilines with sensitive functional groups can be readily prepared. This surrogate has also been used for the synthesis of indoles from 2-halophenols using palladium catalyzed cross coupling reaction as the key step.     

Fluorogenic derivatization of aryl halides based on the formation of biphenyl by Suzuki coupling reaction with phenylboronic acid

The fluorogenic derivatization method for aryl halide was developed for the first time. This method was based on the formation of fluorescent biphenyl structure by Suzuki coupling reaction between aryl halides and non-fluorescent phenylboronic acid (PBA). We measured the fluorescence spectra of the products obtained by the reaction of p-substituted aryl bromides (i.e., 4-bromobenzonitrile, 4-bromoanisole, 4-bromobenzoic acid ethyl ester and 4-bromotoluene) with PBA in the presence of palladium (II) acetate as a catalyst. The significant fluorescence at excitation maximum wavelength of 275–290 nm and emission maximum wavelength of 315–350 nm was detected in all the tested aryl bromides. This result demonstrated that non-fluorescent aryl bromides could be converted to the fluorescent biphenyl derivatives by the coupling reaction with non-fluorescent PBA. We tried to determine these aryl bromides by HPLC-fluorescence detection with pre-column derivatization. The aryl bromide derivatives were detected on the chromatogram within 30 min without any interfering peak derived from the reagent blank. The detection limits (S/N = 3) for aryl bromides were 13–157 fmol/injection.     

环钯化二茂铁亚胺-三苯基膦配合物的合成、表征及催化Suzuki反应研究

为筛选高效催化Suzuki反应的催化剂, 合成了3种新的环钯化二茂铁亚胺-三苯基膦配合物2~4, 经元素分析(或HRMS)、 红外光谱和核磁共振谱对其结构进行了表征, 并通过X射线单晶衍射测定了化合物3的晶体结构. 这些化合物容易合成, 在空气和溶液中稳定, 可用作芳基溴及杂芳基溴与苯基硼酸偶联的Suzuki反应催化剂. 使用摩尔分数为0.01%的催化剂3, 以2倍量的K3PO4为碱, 于110 ℃下, 在甲苯中反应5~15 h, 使具有不同电子和位阻效应的取代芳基溴及杂芳基溴能以较高的产率与苯基硼酸反应生成偶联产物; 与溴苯相比, 带吸电子基的溴苯反应活性较高, 催化剂的摩尔分数降低至0.001%时, 仍能得到较高产率, 而带强给电子基的溴苯如4-溴苯甲醚及带邻位取代基的溴苯在其它条件相同时, 需要延长反应时间才能得到较高的产率.     

Use of tetrahydropyrimidinium salts for highly efficient palladium-catalyzed cross-coupling reactions of aryl bromides and chlorides

New, sterically demanding 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (2) as NHC precursors have been synthesized and characterized. These salts, in combination with palladium acetate, provided active catalysts for the cross-coupling of aryl chlorides and bromides under mild conditions. The catalytic system was applied to the Heck, Suzuki and benzaldehyde (Kumada) coupling reactions. Catalyst activity was found to be influenced by the presence of a methoxy group on the ring of the p-position of benzyl substituent of the ligand precursor.     

A direct functionalization of tertiary alkyl bromides with O-, N-, and C-nucleophiles

Silver oxide used in stoichiometric amounts promoted the direct functionalization of tert-alkyl bromides and provided the desired adducts in 39-96% isolated yield. Reaction of tert-bromides with carboxylic acids yielded esters, with alcohols and phenols yielded alkyl and aryl ethers, with amines and anilines yielded selectively mono-alkylated amines and anilines, and with a C-nucleophile yielded an all-carbon quaternary hydrocarbon. The method was applied to a sequential alkylation of a primary amine with two different alkyl bromides yielding selectively a tertiary amine with three different substituents in one-pot.     

Synthesis of unsymmetrical aroyl acyl imides by aminocarbonylation of aryl bromides.

Aroyl imides were prepared by a palladium-catalyzed aminocarbonylation reaction of aryl bromides with carbon monoxide and primary amides in good yields (58-72%). The reactions were carried out under mild conditions (5 bar, 120 degrees C) using 1 mol % of a palladium phosphine complex. Several aryl bromides were reacted with formamide, acetamide, benzamide, and benzenesulfonamide, respectively. For activated aryl bromides, a phosphine-to-palladium ratio of 2:1 was sufficient, but less reactive aryl bromides required a ligand-to-palladium ratio of 6:1 in order to stabilize the catalyst and achieve full conversion. The imides were very sensitive to aqueous basic conditions and were easily converted to aroyl amides or benzoic acids.