Heck homogeneous

Much of the recent interest in insertion reactions undeniably stems from the emphasis placed on development of homogeneous catalysis as a rational discipline. One or more insertion is involved in such catalytic processes as the hydroformylation (31) or the polymerization of olefins 26, 75) and isocyanides 244). In addition, many insertion reactions have been successfully employed in organic and organometallic synthesis. The research in this general area has helped systematize a large body of previously unrelated facts and opened new areas of chemistry for investigation. Heck 114) and Lappert and Prokai 161) provide a comprehensive compilation and a systematic discussion of a wide variety of insertion reactions in two relatively recent (1965 and 1967) reviews. 

HCR Homogeneous catalytic reaction including hydrogenation, Heck coupling, and Suzuki reaction. 

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... 

To overcome this drawback, we studied the arylation of diethyl 2-vinyl-[l,3]-dioxolane-4,5-diacetate 2 with several bromo polyaromatic and heteroaromatic substrates (Table 21.1 and Scheme 21.4). In parallel, the Heck coupling of several vinyl dioxolane derivatives with aryl bromides was studied in the presence of homogeneous catalysts (Table 21.1). 

Homogeneity/Heterogeneity via Application of Insoluble Metal Scavengers Application to Heck... 

Stevens, P.D., Li, G.F., Fan, J.D., Yen, M. and Gao, Y. (2005) Recycling of homogeneous Pd catalysts using superparamagnetic nanoparticles as novel soluble supports for Suzuki, Heck, and Sonogashira cross-coupling reactions. Chemical Communications (35), 4435-4437. 

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-... 

Bis(pyrazolyl)borate copper complex 47 has been employed as a catalyst in the homogeneous and heterogeneous styrene epoxidation reactions <00JCS(CC)1653>. Pyrazole palladacycles 48 have proven to be stable and efficient catalysts for Heck vinylations of aryl iodides <00JCS(CC)2053>. An asymmetric borane reduction of ketones catalyzed by N-hydroxyalkyl-/-menthopyrazoles has been reported <00JHC983>. 

Several important industrial applications of the Heck reactions are known. The world s largest producer of Naproxen is Albemarle and they make Naproxen using two homogeneously catalysed steps, a Heck reaction and a palladium catalysed hydroxycarbonylation. The last step is carried out using palladium without chiral ligand and the enantiomers obtained are separated, see Figure 13.18. 

In Figure 13.19 we have shown a route to L-699,392 published by Merck involving three steps based on homogeneous catalysts, viz. two Heck reactions and one asymmetric hydrogen transfer reaction, making first an alcohol and subsequently a sulphide [21], Stoichiometric reductions for the ketone function have been reported as well [22] and the Heck reaction on the left-hand side can be replaced by a classic condensation reaction. L-699,392 is used in the treatment of asthma and related diseases. 

Our attention was next drawn to palladiiun-catalyzed Heck condensations of aryl hahdes [38,39]. These are commonly conducted at temperatures of 80-140 °C in higher-boihng solvents such as DMF. Under appropriate conditions all products and by-products remain soluble at room temperature. They therefore represent excellent test reactions for the protocols in Fig. 1. For homogeneous moleciflar catalysts, palladium hahdes are believed to be... 

Homogeneous Catalysis in Supercritical CO2 Using Dendrimer-Encapsulated Metal Particles Heck Chemistry... 

The Mizoroki-Heck reaction in liquid imidazolium salts as the solvent is a special case of an in situ system Under the reaction conditions NHC complexes of palladium are formed as the active catalyst from the solvent and the ligand-free palladium precursor. In general, ionic liquids are novel reaction media for homogeneous catalysis. They allow easy separation of product and catalyst after the reaction. ... 

---