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Heck reaction dioxide

Apart these cases, many other reactions have been investigated, including carbo-nylations, Heck reactions, vinyl substitutions, and hydrosylation. In general, based on available data, it is difficult to establish whether these studies could extend beyond the laboratory scale. However, as Eric Beckman has stressed, when reviewing the use of supercritical or near-critical carbon dioxide in green chemical syntheses [26], the role of these studies in demonstrating the extreme versatility of... [Pg.19]

Bhanage BM, Ikushima Y, Shirai M et al (1999) Heck reactions using water-soluble metal complexes in supercritical carbon dioxide. Tetrahedron Lett 40(35) 6427-6430... [Pg.7]

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. ... [Pg.87]

Heterocycles. 5-Vinyloxazolidin-2-ones expel carbon dioxide and then incorporate CO to form dihydropyridones. 3.4-Cycloindoles are accessible from pen -nitro 1-methylenetetralin and analogues by a reductive cyclization process. Interestingly, the simplest way to prepare the substrates is by an intramolecular Heck reaction. [Pg.328]

The Heck reaction of allenyl catbinols under carbon dioxide leads to cyclic carbonates."... [Pg.332]

Employing the same dendrimer-stabilized palladium colloids for Heck reactions in supercritical carbon dioxide, after 24 h reaction time and 55% conversion no further reaction was observed for reasons not clarified. Remarkably, methyl 2-phenylacrylate was formed exclusively instead of the expected methyl cinnamate (Scheme 1) [37]. [Pg.802]

Recently, a combination of fluorous substituents and a sugar-derived structure allowed the preparation of the scC02-soluble copolymer 53 as a novel phase-transfer catalyst (Figure 4.8). ° Dendrimers with fluorous substituents were also prepared for the same use. ° They are soluble in dense carbon dioxide and can solubilize otherwise C02-insoluble compounds such as Pd-nanoparticles (Scheme 92). The resulting dendrimer-encapsulated Pd catalyzes the hydrogenation of styrene and the Heck reaction of phenyl iodide. [Pg.170]

In the last decade, a lot of attention has been paid to environmental aspects. As to the Mizoroki-Heck reaction, environmentally benign media currently involved in the design of catalytic systems encompass supercritical carbon dioxide (scCOa), fluorous systems, water and aqueous systems, solvent-free systems [66]. In this context, it should be noted that the so-called solvent-free reactions are actually not literally such, but are performed in media composed of substrates and often liquid amine. This was described as early as in 1972 by Heck himself [2, 8] (microwave heated version [53]). Amines are good coordinating solvents during the reaction, the amine is transformed into amine salt, which, being a major constituent or reaction mixture in the absence of a true solvent, adds to the net media polarity. [Pg.64]

Shezad, N., Clifford, A.A. and Ra5mer, C.M. (2001) Suppression of double bond isomerisation in intramolecular Heck reactions using supercritical carbon dioxide. Tetrahedron Lett., 42, 323-5. [Pg.526]

Kayaki, Y., Noguchi, Y. and Ikariya, T. (2000) Enhanced product selectivity in the Mizoroki-Heck reaction using a supercritical carbon dioxide-liquid biphasic system. Chem. Commun., 2245-6. [Pg.527]

Bhanage, B.M., Fujita, S.-i. and Aral, M. (2003) Heck reactions with various types of palladium complex catalysts application of multiphase catalysis and supercritical carbon dioxide. [Pg.527]

Thus, oxidation of the allylic alcohol 363 to the corresponding aldehyde in the presence of a large excess of manganese dioxide initiated the domino oxidation/Diels-Alder/hetero-Diels-Alder sequence. After formation of 366 via an endo-E-syn transition state, the terminal aldehyde 367 then gave the tetracycle 364 in the concluding hetero-Diels-Alder step in 28% yield after 2 days. Intermediate 364 was then further transformed into the natural product 365 in an additional 14 steps, featuring an intramolecular Heck reaction and an iridium-catalyzed isomerization. [Pg.571]

Some of the latest developments in terms of substrates for the Heck reactions are nitrophenyl benzoates [55], acyl benzoates (mixed anhydrides) [236], and substituted benzoic acids [53]. For the last two, the leaving groups are carbon dioxide and carbon monoxide, respectively. A variety of alkenes have been coupled with these substrates. While esters and anhydrides presumably react in a catalytic cycle like that of the classical Heck reaction [237], arenecarboxylic acids, when treated with an equimolar amount of a silver salt as reoxidant, appear to undergo a nonclassical Heck reaction as demonstrated by the coupling with 2-cyclohexenone to give a 3-arylcyclohexenone. [Pg.555]

Some reactions of Pd(PPh3)4 are given in Fig. 5.18. The platinum derivative behaves similarly. Sulphur dioxide acts as a Lewis acid. The reactions with alkyl halides usually follow the Sj 2 mechanism, although free radical pathways can also participate. The reactions of aryl halides, which are normally rather unreactive towards nucleophiles are of interest. The palladium complexes catalyse the arylation of alkenes (the Heck reaction) by the following cycle ... [Pg.182]

In this process, carboxylic acids and olefins are converted to vinylarenes in the presence of palladium in catalytic amounts and silver in overstoichiomettic amounts (Scheme 4). It is initiated by formation of a silver arenecarboxylate salt, which then reacts with a palladium(ll) halide complex (a) to give the silver halide and palladium carboxylate b. The extrusion of carbon dioxide, and thus the conversimi of the carboxylate to the organometallic species c, occurs within the ligand sphere of palladium. The subsequent steps, i.e., insertion of the olefin into the palladium-carbon bond, internal rotation, and (3-hydride elimination, correspond to the classical Heck reaction [26]. An additional oxidation step converts the palladium(0) species f back to palladium(ll). It is this oxidation by silver that... [Pg.125]

Supercritical fluids Carbon dioxide forms a supercritical phase under relatively low temperatures and pressures and it therefore has been explored as a solvent for tbe Heck reaction. Following the reaction, the gas can be collected and recycled, allowing the design of true waste-free technology. The dielectric constant of supercritical CO2 is similar to pentane and therefore modified catalytic systems are often required to aid solubility.Unusually, one of the best catalytic precursors in supercritical CO2 is Pd(OCOF3)2, a strong electrophile and oxidant. Heck reactions in supercritical water have also been investigated. ... [Pg.27]

The 1,2-benzothiazepine 1,1-dioxides 126 were prepared in fair yields (e.g. 126, R = H, Ar = p-ClC6H4, 52%) by a Heck coupling on the precursors 125, which were obtained in turn from an aza Baylis-Hillman reaction involving the appropriate sulfonamide, aldehyde, and methyl acrylate reactants <06TL8591>. [Pg.455]

Heck, W. W. Plant injury induced by photochemical reaction products of propylene-nitrogen dioxide mixtures. J. Air Pollut. Control Assoc. 14 255-261, 1. ... [Pg.568]

Gordon and Holmes32 used a supported triphenylphosphine-Pd(II) complex as an effective catalyst for Heck and Suzuki couplings in supercritical carbon dioxide (entry 27). After optimization of the amine base for the reaction, the final products have been isolated in good yields and high purity with no traces of metal. [Pg.359]

Tin Reagents. Vinyltrialkyltin reagents can be used for introduction of alkenyl substituents into the 4-position in N-protected imidazoles 130 (Scheme 55). In this particular case alkenylation reaction under Heck conditions was unsatisfactory due to facile homocoupling of the heterocycle. A related series of reactions has been used for introduction of an allylic alcohol substituent into the imidazole 4-position in a ribosylimidazole nucleoside 131.Vinylation of 5-bromo-3-diethylamino-4-(4-methoxyphenyl)isothiazole 1,1-dioxide 132 with vinylstannane reagents can be used for the preparation of 5-alkenylated isothiazole 1,1-dioxides. "... [Pg.448]


See other pages where Heck reaction dioxide is mentioned: [Pg.95]    [Pg.215]    [Pg.95]    [Pg.95]    [Pg.242]    [Pg.215]    [Pg.95]    [Pg.16]    [Pg.77]    [Pg.329]    [Pg.141]    [Pg.143]    [Pg.188]    [Pg.121]    [Pg.164]    [Pg.172]    [Pg.126]    [Pg.750]    [Pg.145]    [Pg.228]    [Pg.750]    [Pg.136]    [Pg.145]    [Pg.614]    [Pg.275]    [Pg.24]   
See also in sourсe #XX -- [ Pg.894 , Pg.895 ]




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