Heck-Suzuki-type reaction

To mention a few synthetic appHcations of trialkylsilanols, trimethylsilanol 4 adds readily to 2-chloroacrylonitrile in diethyl ether in the presence of triethylamine as triethylammonium trimethylsilanolate followed by ehmination of triethylamine hydrochloride to give 99 [32] (cf. discussion of the strongly nucleophihc properties of ammonium trimethylsilanolate 155 in Section 4.2.1). The stable potassium trimethylsilanolate 97 has also been used for the saponification of esters (Section 4.7). Dimethylphenylsilanol 100 adds readily to a,y9-unsaturated carbonyl compounds such as methyl vinyl ketone 764 in the presence of Pd(OAc)2 in a Heck-Suzuki-type reaction to give the sihcon-free /9-phenylmethylvinylketone 101 [33]. 

A drawback of the Heck-type reaction is that it is not strictly regioselective [119]. Depending on the substituents >1% of 1,1-diarylation is observed. Soluble 2,5-dialkoxy-PPVs 63 or 2-phenyl-PPV PPPV 93, without 1,1-diarylated moieties, were synthesized by Heitz et al. in a Suzuki-type cross coupling of substituted 1,4-phenylenediboronic acids and fran5-l,2-dibromoethylene, catalyzed by Pd(0) compounds [120]. However, about 3% of biaryl defect structures are observed in the coupling products (M up to 12,000), resulting from homocoupling of boronic acid functions. 

Other successful examples of catalysts containing NHC ligands are found in palladium- and nickel-catalyzed carbon-carbon bond formations. The catalyst development with these metals has focused in particular on Heck-type reactions, especially the Mizoroki-Heck reaction itself [Eq. (42)] and various cross coupling reactions [Eq. (43)], e.g., the Suzuki-Miyaura reaction ([M] = and the Kumada-Corriu reaction ([M] = MgBr). " Related reactions like the Sonogashira coupling [Eq. (44)]326-329 Buchwald-... 

Heck-, Suzuki- and Stille-type Couplings - The Heck reaction, palladium-catalysed coupling of aryl or vinyl halides with alkenes or alkynes, is an extremely useful synthetic method. Only recently have Heck reactions been performed in aqueous media, probably due to the perception that water must be carefully... 

Choudary, B.M., Madhi, S., Chowdari, N.S., Kantam, M.L. and Sreedhar, B., Layered double hydroxide supported nanopalladium catalyst for Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes, J. Am. Chem. Soc., 2002, 124, 14127-14136. 

Heck and Suzuki type couplings have been described by Fu [2] et al. The reaction of chlorobenzene and styrene in refluxing dioxane in the presence of [Pd2(dba)3 ] and the electron rich tri-tert.-butyl-phosphane [eq. (a)] gives rise to trans-stilbene in 83% yield. Besides the choice of the ligand - aryl phosphanes, tri-n-butyl-phosphane or tri-cyclo-hexyl-phosphane show no conversion - the base is also crucial for success. Cesium carbonate gives the best results, although the cheaper potassium phosphate gives comparable yields. 

Palladacycles [17] have been established as important class of catalysts, an unusual phosphine-free sulfur containing catalyst was introduced by Zim [18] et al. A phosphinite based palladacycle [19] proved to be very efficient in Suzuki coupling reactions. An N,P-Ligand type was synthesized by Kocovsky [20] et al. Tridentate pincer ligands [21] have been proved use-fill in the Heck reaction. Recent developments regarding Heck (22] and Suzuki [23] reactions have been reviewed by Fu and Littke. A new catalyst especially suitable for Heck couplings has been introduced by Beller [24] et al. 

Aryl diazonium salts can be used coupled with alkenes in a Heck-Uke reaction (12-15)7 Other reactive aryl species also couple with aryldiazonium salts in the presence of a palladium catalyst7 A Suzuki type coupling (13-9) has also been reported using arylboronic acids, aryldiazonium salts and a palladium catalyst/ ... 

A new type of soluble polystyrene-supported palladium complex was synthesised (Figure 6.1) as an excellent and recyclable palladacycle catalyst for carbon-carbon bond formation in Heck, Suzuki and Sonogashira reactions to give high yields of the desired products. 

Intramolecular Reaction of Aryl and Vinyl Halides Heck-, Suzuki-, and Stille-Type Reactions... 

Figure 1.6. Test reaction for (a) Suzuki-type and (h) Heck-type cross-coupling using palladium nanoparticles stahihzed in SPB particles as a catalyst.

The reproducibility was found to be very good for palladium nanoparticles as catalyst of both Suzuki- and Heck-type reactions. In four runs the products were removed by ether and new starting materials were added to the water phase. We found that Pd SPB could be used repeatedly without loss of activity. After these four... 

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