Synthesis of polyhydroxylated ester analogs of the stilbene resveratrol using decarbonylative Heck couplings

Protected 3,5-hydroxy-benzoyl chlorides 3 were coupled with styrenes 4 to give hydroxylated stilbenes, analogs of resveratrol, an important antioxidant disease preventative agent isolated from grape skins and other dietary sources. Levulinate and chloroacetate protecting groups allowed for the selective production of mono- and di-acetate variations under palladium-N-heterocyclic carbene (NHC) catalyzed decarbonylative coupling conditions. Fluorinated analogs were also produced using Heck conditions with bromofluorobenzenes. Human HL-60 cell assays showed the 4′-acetoxy variant 11 to have improved activity (ED₅₀ 17 μM) relative to resveratrol (24 μM).     

环钯-[PPh4]Br体系催化氯代芳烃的Heck芳基化反应研究

以氯代芳烃为底物，季鏻盐[PPh4]Br为助催化剂，用于环钯催化的Heek芳基化反应．结果表明，在环钯-[PPh4]Br催化体系中，以Na2CO3作为碱性试剂，使用0．3mol％Pd的环钯催化剂催化氯苯的Heek反应，就可得到比较高的产率（88％）和转化率（90％）．对于大部分卤代芳烃Heck反应而言，环钯-[PPh4]Br是一种有效的催化体系，即使是对含推电子基团的不活泼的氯代芳烃，在此体系中也能获得比较好的结果．此外，文中还探讨了反应温度、[PPh4]Br／Pd比值及催化剂回用对反应活性的影响．     

Palladium-catalyzed Heck reaction of in-situ generated benzylic iodides and styrenes

A palladium-catalyzed Heck reaction of in-situ generated benzylic iodides and styrenes has been achieved. The reaction proceeds in a one-pot manner through 1) addition perfluoroalkyl iodides to styrenes to give benzylic iodides, 2) followed by a palladium-catalyzed Heck coupling of the resulting benzylic iodides with the same alkenes in high regio- and stereoselectivity. A variety of perfluoroalkylated alkenes were obtained in moderate to excellent yields.     

Chemoselective Heck arylation of acrolein diethyl acetal catalyzed by an oxime-derived palladacycle

A dimeric 4-hydroxyacetophenone oxime-derived palladacycle has been used as a very efficient precatalyst for the chemoselective arylation of acrolein diethyl acetal to give either cinnamaldehyde derivatives or 3-arylpropanoate esters by proper choice of the reaction conditions. The synthesis of cinnamaldehyde derivatives can be performed by Heck reaction of acrolein diethyl acetal with iodo-, bromo- or chloroarenes in N,N-dimethylacetamide (DMA) using K₂CO₃ as base at 120 °C and tetra-n-butylammonium acetate (TBAA) and KCl as additives, followed by acid workup. In the case of 3-arylpropanoate esters the corresponding arylation of acrolein diethyl acetal with iodoarenes can be performed at 90 °C in aqueous DMA using (dicylohexyl)methylamine as base, whereas for bromoarenes the reaction has to be performed at 120 °C using tetra-n-butylammonium bromide (TBAB) as additive. Alternatively, this process can be performed under microwave irradiation. These couplings take place in good yields and with lower catalyst loading than with palladium(II) acetate as well as in shorter reaction times and with lower excess of acrolein diethyl acetal.     

Palladium-catalyzed Heck coupling reactions using different fluorinated phosphine ligands in compressed carbon dioxide and conventional organic solvents

Palladium-catalyzed Heck reaction of iodobenzene and styrene was investigated in compressed CO₂ using different fluorinated phosphine compounds as ligands at a temperature of 70 °C. The reaction mixture is a single phase at 12 MPa but biphasic at 8 MPa, a little higher than the critical pressure of pure CO₂ under the reaction conditions used. Although the solubility of fluorinated ligands is very high in dense CO₂, they have marginal improvements in Heck conversion in this medium compared with a non-fluorinated ligand of triphenylphosphine. The activity of palladium complexes strongly depends on the kind of phosphine compound used, in the order of bis(pentafluorophenyl)phenylphosphine (III)>triphenylphosphine (I), tris(pentafluorophenyl)phosphine (IV)>diphenyl(pentafluorophenyl)phosphine (II), tris(p-fluorophenyl)phosphine (V)>tris(p-trifluoromethyl phenyl)phosphine (VI), 1,2-bis[bis(pentafluorophenyl)phosphino]ethane (VII), for the homogeneous reaction at 12 MPa. This order of effectiveness of these ligands is different from those obtained in conventional organic solvents. Hexane, toluene, ethanol, and N-methylpyrrolidone (NMP) showed maximum conversions with the ligands VI, IV, V and VII, respectively. The conversion in CO₂ with the ligand III is comparable with those in polar solvents of ethanol and NMP, and larger than those in hexane and toluene in the presence of the best ligands. The dense CO₂ may affect the specific activity of palladium complex catalysts and/or the reactivity of reacting species. Small quantities of fluorinated products were observed to form at high pressure of CO₂ and this is direct evidence of P–C bond cleavage during Heck reaction in dense CO₂. The activity of palladium complexes with those ligands is higher in more polar solvent.     

Hybrid polyoxometalate palladacycles: DFT study and application to the Heck reaction

The phosphovanadotungstate polyanion [P₂W₁₅V₃O₆₂]^9? is a powerful support to stabilize palladacycles conjugated to the inorganic framework via an organic ligand. The insertion can be directed toward sp² or sp³ C–H insertion upon appropriate choice of the substitution pattern on the organic ligand. DFT modeling indicates that the strong withdrawing effect of the POM transmitted through the conjugated carbonyl was responsible for this easy insertion. The palladacycles led to the formation of stilbene via a Mizoroki–Heck reaction. However it is likely that the POMs act as Pd-reservoirs for the formation of nanoparticles.     

Pd/Cu-free Heck and Sonogashira coupling reactions applying cobalt nanoparticles supported on multifunctional porous organic hybrid

A new heterogeneous cobalt catalyst has been synthesized by immobilizing Co species onto a nitrogen-rich porous organic polymer (Co@imine-POP). The heterogeneous catalyst synthesized was efficient in Heck and Sonogashira cross-coupling reactions in green media under mild reaction conditions without inert air and phase transfer agents. This phosphine-, copper-, and palladium-free catalyst was stable under the reaction conditions and could be reused for at least eight successive runs without a discernible decrease in its catalytic activity.     

Heck reactions of aryl halides in phosphonium salt ionic liquids: library screening and applications

The Heck cross-coupling of aryl iodides and bromides with olefins proceeds in the phosphonium salt ionic liquid trihexyl(tetradecyl)phosphonium chloride (THP-Cl) in excellent yields. Furthermore, it is shown that the counter anion matched to the phosphonium cation exerts a measurable effect on the overall yield.     

Short synthesis of bis-NHC-Pd catalyst derived from caffeine and its applications to Suzuki, Heck, and Sonogashira reactions in aqueous solution

A short and efficient synthesis of a bis-NHC-palladium catalyst simply prepared from caffeine in two steps was reported. The air and moisture stable Pd catalyst can be used as a good catalyst in running Suzuki-Miyaura, Mizoroki-Heck, and Sonogashira reactions in aqueous solution.     

Controlled mono and double Heck reactions in water catalyzed by an oxime-derived palladacycle

The mono and β,β-diarylation of α,β-unsaturated carbonyl compounds with electron-deficient and electron-rich aromatic iodides in water is described. These reactions are catalyzed by the p-hydroxyacetophenone oxime-derived palladacycle 1 by controlling the stoichiometry of the aryl iodide and the alkene as well as the loading of the palladium catalyst. This one-pot protocol is performed in refluxing water and (dicyclohexyl)methylamine as base under thermal or microwave conditions and in the absence of an inert atmosphere.     

含有酯基二茂铁亚胺环钯化合物催化Suzuki和Heck反应

合成并表征了系列含有酯基二茂铁亚胺环钯化合物.结果表明,该系列环钯催化剂在纯水或有机溶剂中均能高效催化Heck和Suzuki偶联反应.     

Efficient Synthesis of Pyridylacrylonitriles via the Heck Reaction

A new synthetic pathway to pyridylacrylonitriles has been developed based on a palladium‐catalyzed Heck reaction. The optimized process and the preparation of related functionalized pyridylacrylonitriles are discussed.     

Suzuki and Heck coupling reactions mediated by palladium complexes bearing trans-spanning diphosphines

Palladium complexes of three trans-spanning diphosphines are examined for effecting C-C coupling reactions. Ten aryl halides of varying electron density were screened in Suzuki coupling reactions with phenylboronic acid and in Heck reactions with styrene. The results are discussed in terms of the unique flexibility and shape of the meta-terphenyl backbone upon which the diphosphine ligand is built.     

钯催化Heck反应制备长共轭生色二苯乙烯衍生物

采用Heck反应合成出6个带有不同推拉电子基团的二苯乙烯衍生物,产率68%～84%.研究了反应物分子结构对Heck偶联反应的影响,对实验条件进行了优化并探讨了其反应机理.结果表明,反应温度120℃,溶剂DMF 和Et3N体积比为2: 1时可以获得较高产率.同时我们还发现,不同的反应物结构对Heck反应产率的影响较大,随着反应物中双键的电子云密度的降低(对甲基苯乙烯>苯乙烯>4-乙烯吡啶),反应产率依次降低;芳卤的反应活性表现为:NO2-Ar-Br>H-Ar-Br>CH3-Ar-Br.     

Heck reactions in monoglyme and diglyme using BmimCl as pre‐ligand

Heck reactions between iodobenzene and methyl acrylate were carried out in monoglyme and diglyme as solvents, using different ligands and palladium sources, and good to high yields were obtained in the production of (E)‐substituted olefins. The ionic liquid BmimCl was successfully utilized as pre‐ligand to substitute triphenylphosphine. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and characterization of phospha-palladacycles and their catalytic properties in the olefination of chloro- and bromoarenes

Acetylacetonates of phospha-palladacycles are new catalysts in the Heck coupling of aryl chlorides and bromides with styrene. Turnover numbers (TON) of much higher than 300,000 and product yields up to 99% are obtained.     

Synthesis of Entacapone by Pd-Catalyzed Heck Coupling Reaction

Synthesis of entacapone from 4-iodo-2-methoxy-phenol with 2-cyano-N,N-diethylacrylamide by palladium-catalyzed Heck reaction, as a key step, is described.     

1,3-Dicarbonyl compounds as phosphine-free ligands for Pd-catalyzed Heck and Suzuki reactions

Some 1,3-dicarbonyl compounds (such as pentane-2,4-dione and 3-oxo-N-phenylbutanamide) were found to constitute highly efficient, yet low-priced and phosphine-free ligands for the Pd-catalyzed Heck and Suzuki reactions of aryl bromides and iodides with very high turnover numbers (ca. 103-104).     

Synthesis, characterization, and applications in Heck and Suzuki coupling reactions of amphiphilic cyclopalladated ferrocenylimines

A series of novel amphiphilic ferrocenylimines and their cyclopalladated complexes of general formula [Fe(η⁵-C₅H₅)(η⁵-C₅H₄CR₁NR₂)] (R₁=H, R₂=C₁₂H₂₅-n4a, R₁=H, R₂=C₁₆H₃₃-n4b, R₁=CH₃, R₂=C₁₂H₂₅-n4c, R₁=CH₃, R₂=C₁₆H₃₃-n4d), [PdCl{[(η⁵-C₅H₅)]Fe[(η⁵-C₅H₃)CR₁NR₂]}]₂ (5a-d), [PdCl{[(η⁵-C₅H₅)]Fe[(η⁵-C₅H₃)-CR₁NR₂]}(PPh₃)] (6a-d), were prepared and characterized by ¹H NMR, ¹³C NMR, ³¹P NMR, IR, HRMS, and elemental analysis. The crystal structures of 5c,d were determined by X-ray crystallography. These amphiphilic cyclopalladated complexes are thermally stable and insensitive to oxygen and moisture. The redox properties of 4a-d, 5a-d, 6a-d were also investigated using cyclic voltammetric technique. Compounds 5a-d, 6a-d displayed good activity in the Heck reaction of a variety of aryl halides with ethyl acrylate or styrene and the Suzuki-Miyaura cross-coupling reaction of aryl bromides with phenylboronic acid in bulk solution. They are also suitable for formation of Langmuir-Blodgett (LB) films.     

Desymmetrisation of a diallyl system by intramolecular Heck reaction

The development of a desymmetrising cyclisation of a benzylic diallyl iodide is reported. The final procedure generates a new quaternary chiral centre in greater than 80% yield giving a highly functionalised methylene indan product suitable for further application in synthesis.