Aryl halides Heck couplings

Arylation or vinylation of aUcenes with aryl or vinyl halides (Heck coupling)... 

In a reaction analogous to the catalytic coupling of aryl halides, Heck 94, 101) found that benzyl and vinyl halides would also undergo the reaction ... 

Reaction medium. By virtue of its attributes supercritical carbon dioxide deserves its increasing applications as a reaction medium in synthesis. These include epoxidation" with oxygen and PhCHO, rhodium-catalyzed hydroboration, Pd(0)-catalyzed 1,4-hydroarylation of enones" and Heck reaction in the presence of Pd-C," carbonylation of aryl halides, Glaser coupling of 1-alkynes (mediated by CuCy using a solid ba.se (NaOAc)," as well as seandium(III) perfluorooctanesulfonate-catalyzed Diels-Alder and hetero-Diels-Alder reaetions. ... 

Oxazoles and benzoxazoles are viable participants in the heteroaryl Heck reaction, whereby the alkyl halide or aryl halide is coupled to the unfunctionalized oxazole. First developed by Ohta and colleagues, it was demonstrated that a diverse array of aromatic heterocycles can be substrates in the reaction with chloropyrazines. While substitution was expected to occur at the 2-position, the reaction with chloropyrazine as the aryl halide resulted in substitution at the 5-position. When benzoxazole is used as the coupling partner, substitution is effected at the 2-position. More recently, a systematic study by Strotman and co-workers has demonstrated that slight modifications of the reaction conditions can allow completely regioselective coupling at either the 2- or 5-position. ... 

Closely related to the Heck reaction is the Sonogashira reaction i.e. the palladium-catalyzed cross-coupling of a vinyl or aryl halide 20 and a terminal alkyne 21 ... 

Carbon-carbon bond formation reactions and the CH activation of methane are another example where NHC complexes have been used successfully in catalytic applications. Palladium-catalysed reactions include Heck-type reactions, especially the Mizoroki-Heck reaction itself [171-175], and various cross-coupling reactions [176-182]. They have also been found useful for related reactions like the Sonogashira coupling [183-185] or the Buchwald-Hartwig amination [186-189]. The reactions are similar concerning the first step of the catalytic cycle, the oxidative addition of aryl halides to palladium(O) species. This is facilitated by electron-donating substituents and therefore the development of highly active catalysts has focussed on NHC complexes. 

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... 

Nanometer size Pd colloids in block copolymer micelles of polystyrene polyvinylpyridine as catalysts have been used is a novel way by Klingelhofer for Heck reaction of C-C coupling of aryl halides with olefins. 

Under all the conditions studied, addition of bare Si02-SH to Heck or Suzuki coupling reactions using a variety of bases, aryl halides and solvents resulted in complete cessation of the catalytic activity (35). These results suggest that catalysis with this precatalyst is also associated with labile palladium species that... 

Heck coupling of aryl halides with n-butylacrylate under m/w irradiation. 

Transition metal-catalyzed transformations are of major importance in synthetic organic chemistry [1], This reflects also the increasing number of domino processes starting with such a reaction. In particular, Pd-catalyzed domino transformations have seen an astounding development over the past years with the Heck reaction [2] - the Pd-catalyzed transformation of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - being used most often. This has been combined with another Heck reaction or a cross-coupling reaction [3] such as Suzuki, Stille, and Sonogashira reactions. Moreover, several examples have been published with a Tsuji-Trost reaction [lb, 4], a carbonylation, a pericyclic or an aldol reaction as the second step. 

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). 

Herrmann WA, Brossmer C, Reisinger CP, Riermaier T, Ofele K, Beller M (1997) Coordination chemistry and mechanisms of metal-catalyzed C-C coupling reactions. Part 10. Palladacycles efficient new catalysts for the Heck vinylation of aryl halides. Chem Eur J 3 1357-1364 Iyer S, Jayanthi A (2001) Acetylferrocenyloxime palladacycle-catalyzed Heck reactions. Tetrahedron Lett 42 7877-7878 Iyer S, Ramesh C (2000) Aryl-Pd covalently bonded palladacycles, novel amino and oxime catalysts di- x-chlorobis(benzaldehydeoxime-6-C,AT)dipalla-dium(II), di- x-chlorobis(dimethylbenzylamine-6-C,A)dipalladium(II) for the Heck reaction. Tetrahedron Lett 41 8981-8984 Jeffery T (1984) Palladium-catalysed vinylation of organic halides under solid-liquid phase transfer conditions. J Chem Soc Chem Commun 1287-1289 (b) idem,... 

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. 

The scope of the multiphasic system was extended to coupling reactions—like the Heck reaction—using a heterogeneous supported catalyst, such as Pd/C. The rationale here lay in the observation that aryl halides were activated in the multiphasic system (as seen for hydrodehalogenation), and that therefore they should also be activated toward C-C coupling reactions. 

Table3. Results obtained from Heck coupling of n-butylacrylate (BA) with aryl halides (X = halide, and R = para substituent) under various conditions using 3-5 mol % Pd...

Olefin that undergoes dihydroxylation is generated in situ from aryl halide and a terminal olefin via Pd-catalyzed Heck coupling. 

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