Palladium Heck coupling

Palladium-catalyzed coupling reactions of organic halides with olefins or dienes (R. F. Heck, 1979) are broad in scope and simple to carry out. Anhydrous conditions or any special technique are not required and most functional groups are tolerated. 

Due to their successful synthesis of 2-(4 -chlorophenyl)-4-iodoquinoline from the corresponding precursor acetylene, Arcadi et al. (99T13233) developed a one-step synthesis of 2,4-disubstituted quinolines via palladium-catalyzed coupling reactions. An example is the Heck reaction of 4-iodoquinoline (131) with a-acetamidoacrylate (132). This one-pot synthesis yielded adduct 133 in 50% overall yield after purification via flash chromatography. 

The coupling reaction of aryl-alkenyl halides with alkenes in the presence of a palladium catalyst and a base is known as the Heck coupling (Scheme 9.4).6 Since the early 1980s, this type of coupling reaction has been used for die syndiesis of poly(arylenevinylene) and related polymers by polymerization of AB- or AA/BB-type of monomers (Scheme 9.5).7... 

Another methodology that is widely used for C-C bond formation is the Heck coupling (Heck, 1985 T.suji, 1995). The Heck reaction involves the palladium-catalysed arylation of olefinic double bonds (Eqn. (12)) and provides an alternative to Friedel-Crafts reactions for attaching carbon fragments to aromatic rings. 

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... 

Most commercial palladium scavengers are designed for use after a reaction - thus at low temperatures. Is the solid poison being considered stable at the temperatures of the reaction Many Heck couplings are used at well over 100°C and some polymeric poisons may bre down under these conditions. This could lead to ineffective poisoning of solution species as well as unwanted interaction of small molecule degradation products with supported palladium species. 

Diazonium salts react with various nucleophiles in water (Eq. 11.62).106 In acidic aqueous solution, p-pheny I e ncbis di azo ni um ion reacts with alcohols more rapidly than it does with water.107 In the presence of nucelophiles such as halides, the substitution products are obtained. Furthermore, diazonium salts of aromatic compounds are excellent substrates for palladium-catalyzed coupling reactions such as the Heck-type reactions in water. 

Therefore, a good catalyst leads to weak fluorescence in the Heck product (15). A relatively small library of 96 known phosphines was tested in the palladium-catalyzed Heck coupling. Several sterically hindered ligands led to high catalyst activity. Fluorescence tags have also been used in the combinatorial search for metal-free catalysts in other types of reaction.42,43... 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

Scheme 7.121 Heck couplings utilizing an oligo(ethylene glycol)-bound SCS-palladium(ll) complex as catalyst.

Scheme 7.122 Heck couplings utilizing palladium on porous glass.

Under microwave heating, the Heck olefinations were achieved in 30-60 min, as opposed to 10-40 h by conventional heating. The recyclable heterogeneous LDH-Pd(0) catalytic system circumvents the need to use expensive and air-sensitive basic phosphines as ligands in the palladium-catalyzed coupling of chloroarenes. This novel Mg-Al layered double-hydroxide (LDH) support in the catalytic system stabilizes the nanopalladium particles and also supplies adequate electron density to the anchored palladium(O) species and facilitates the oxidative addition of the deactivated electron-rich chloroarenes. 

Typically, the Pd species for Heck couplings are homogeneous catalysts, stabilized by air-sensitive ligands. They present economic and environmental problems regarding separation, regeneration and reuse. These difficulties can be diminished with heterogeneous catalysts that are more easily recoverable from the reaction mixture. As mentioned in Sect. 2.6, a catalyst consisting of palladium metal deposited on por-... 

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). 

Figure 6.19. Heck coupling catalysed by fluorinated f/y-l i iBINAP palladium complex.[63]...

Arylation of cycloalkenes.1 Aryl halides undergo Heck coupling with cy-cloalkenes in the presence of a palladium catalyst. The reaction involves addition of an arylpalladium intermediate to the double bond followed by elimination of a palladium hydride. 

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. 

Fig. 27. Heck coupling of substituted arylhalides to acrylates in the presence of sc(C02) soluble PPI dendrimers containing palladium nanoparticles is highly selective for the non-standard 1,1-substituted product...

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... 

Palladium-catalyzed coupling of organostannanes, 50, 1 Palladium intermediates in Heck reactions, 60, 2... 

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