Heck reaction coupling

When Heck reactions and other C-C coupling reactions are carried out in imidazolium-based ionic liquids, the base can react with the acidic proton on the 

The problem with carbene formation is that they can displace the phosphine ligands attached to the catalyst and deactivate the catalyst. In general, the active catalyst is a palladium(O) compound and this low oxidation state is best stabilized by very bulky phosphines such as P(lBu)3 mentioned above. 

The reaction between iodobenzene and methyl acrylate in scCC 2 using the Pd(OAc)2/fluorous-derivatized phosphine catalyst gave a superior yield of methyl cinnamate compared to the same reaction in a conventional organic solvent. The 

Heck reaction has some important applications in industry because it is one of the effective tools for the formation of new C-C bonds [49]. The traditional Heck reaction is performed with a Pd catalyst with phosphine ligands in the presence of a base under an inert atmosphere. However, the expensive Pd complex is often lost at the end of the reaction, which limits the large-scale application of Heck reactions. On the other hand, phosphine ligands, especially the electron-rich ones, are often toxic, and water and air sensitive. For industrial application, it is important to have good strategies for catalyst-product separation and catalyst recycling. SIL catalyst is one of the promising alternatives for the development of eco-friendly processes. 

Stable and thermally stable to allow easy use and storage, which is advantageous for wide appHcation in various Pd-catalyzed reactions. Besides, PEG-SlL([PEGmim]Cl) was synthesized and applied to the Pd-catalyzed Heck couphng reactions with excellent yields of the products [49b]. Furthermore, the Pd(OAc)2/[PEGmim]Gl catalytic system could be recycled five times without obvious deactivation. 

1 Palladium-catalysed multiple and asymmetric arylations of vinyl ethers 

CARRYING CO-ORDINATING NITROGEN AUXILIARIES SYNTHESIS OF ARYLATED KETONES AND ALDEHYDES 

1 Triarylation synthesis of A,./V-dimethyl-2-[l,2,2-(triaryl)ethenyloxy] ethanamines with subsequent hydrolysis furnishing 1,2,2-triaryl 

3 Asymmetric Heck arylation synthesis of 2-aryl-2-methyl 

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The first reaction pathway for the in situ formation of a metal-carbene complex in an imidazolium ionic liquid is based on the well loiown, relatively high acidity of the H atom in the 2-position of the imidazolium ion [29]. This can be removed (by basic ligands of the metal complex, for example) to form a metal-carbene complex (see Scheme 5.2-2, route a)). Xiao and co-workers demonstrated that a Pd imida-zolylidene complex was formed when Pd(OAc)2 was heated in the presence of [BMIMjBr [30]. The isolated Pd carbene complex was found to be active and stable in Heck coupling reactions (for more details see Section 5.2.4.4). Welton et al. were later able to characterize an isolated Pd-carbene complex obtained in this way by X-ray spectroscopy [31]. The reaction pathway to the complex is displayed in Scheme 5.2-3. 

OUTLINE OF THE CATALYTIC CYCLE FOR THE HECK COUPLING REACTION... 

Andrus and Liu exploited a Pd(NHC) decarbonylative Heck coupling reaction in the total synthesis of resveratrol [59], The catalyst was formed in situ with Pd(OAc), and IPr HCl. 

The Heck coupling reaction appeared to be a route of choice to achieve the synthesis of the modified-DIOP ligands. We previously studied the palladium-catalyzed coupling of acrolein and acrolein acetals with several polyaromatic and heteroaromatic bromides either in the presence of homogeneous or heterogeneous catalytic systems (6, 7). After optimization of the reaction conditions, high conversions and selectivities were achieved except with anthracenyl derivatives (8). Based on these results, we developed the synthesis of the desired ligands. The... 

The aqueous Heck coupling reaction was also used for the synthesis of unprotected branched-chain sugar. In the media of DMF-H2O (5 1) and the use of Pd(dba)2 and P(o-tol)3 the Heck reaction proceeded smoothly to give the coupling product with high yield (up to 84%) (Eq. 3.38).148... 

Water-soluble phosphine ligands containing m-guanidinium moieties were synthesized and applied to aqueous Heck coupling reactions.149 High temperature appears beneficial for Heck-type coupling of simple alkenes in water.150... 

Reaction of organic halides with alkenes catalyzed by palladium compounds (Heck-type reaction) is known to be a useful method for carbon-carbon bond formation at unsubstituted vinyl positions. The first report on the application of microwave methodology to this type of reaction was published by Hallberg et al. in 1996 [86], Recently, the palladium catalyzed Heck coupling reaction induced by microwave irradiation was reported under solventless liquid-liquid phase-transfer catalytic conditions in the presence of potassium carbonate and a small amount of [Pd(PPh3)2Cl2]-TBAB as a catalyst [87]. The arylation of alkenes with aryl iodides proceeded smoothly to afford exclusively trans product in high yields (86-93%) (Eq. 61). 

The incredibly powerful and versatile Heck coupling reaction has found enormous utility in indole ring synthesis and in the elaboration of this important heterocycle. Due to the enormity... 

Bars, J.L., Specht, U., Bradley, J.S., and Blackmond, D.G., A catalytic probe of the surface of colloidal palladium particles using heck coupling reactions, Langmuir, 15, 7621, 1999. 

Triphenylphosphine-Functionalized Amphiphiles for Rhodium-Catalyzed Hydroformylation and Palladium-Catalyzed Heck Coupling Reaction... 

In the second series of experiments, O. Nuyken et al. investigated the Heck reaction of iodobenzene with styrene as a model for the numerous palladium-catalyzed coupling reactions (Scheme 6.6) [54]. In the literature only a few Heck coupling reactions of hydrophobic substrates in aqueous solution are known. The most detailed study has been performed by Jeffery et al. on the model reaction of iodobenzene with methylacrylate in the presence of tetrabutylammonia salts. Product yield was at least 95% after 2 h reaction time at 50 °C in pure aqueous solution [55], however more... 

Shore and coworkers [64] used a capillary reactor with a Pd thin film and microwave-assisted continuous-flow conditions for Suzttki-Miyara and Heck coupling reactions. The Pd film was prepared by passing Pd(OAc)2 solution into the 1150 pm eapillary at 150°C resulting in a highly porous catalyst composed of nanometer-size grains. 

Heterogenization of homogeneous metal complex catalysts represents one way to improve the total turnover number for expensive or toxic catalysts. Two case studies in catalyst immobilization are presented here. Immobilization of Pd(II) SCS and PCP pincer complexes for use in Heck coupling reactions does not lead to stable, recyclable catalysts, as all catalysis is shown to be associated with leached palladium species. In contrast, when immobilizing Co(II) salen complexes for kinetic resolutions of epoxides, immobilization can lead to enhanced catalytic properties, including improved reaction rates while still obtaining excellent enantioselectivity and catalyst recyclability. 

Scheme 27 Synthesis of P-lactam and olefination by Heck coupling reaction...

The polymers are synthesized by utilizing the Heck coupling reaction. Their structures are shown as polymers V to VII (Scheme 6). The metal-to-ligand charge transfer of the ruthenium complexes of polymer VI results in... 

Hudlicky et al. described an elegant strategy based on two intramolecular Heck coupling reactions for the enantioselective synthesis of codeine from 2-phenylbro-moethane (Scheme 10.36).64... 

In the presence of palladium(II) and silver(I) salts, arene carboxylates could be converted to aryl palladium species, which were engaged in Heck coupling reactions.90 Since the more electrophilic palladium trifluoroacetate proved to be the bestcatalyst, decarboxylation probably occurred by aromatic electrophilic substitution... 

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