Alkenes Heck reaction

Aryl coupling reactions" Heck reaction Alkene Arylalkene 6 71 71-83... 

Larhed, M., Hallberg, A. The Heck reaction (alkene substitution via carbopalladation-dehydropalladation) and related carbopalladation reactions, in Handbook of Organopalladium Chemistry for Organic Synthesis (eds. Negishi, E.-i.,De Meijere, A.), 1,1133-1178 (Wiley-... 

IV.2 The Heck Reaction (Alkene Substitution via Carbopalladation-Dehydropalladation) and Related Carbopalladation Reactions... 

Negishi E, de Meijere A (2002) Handbook of organopalladium chemistry for organic synthesis, Chapter IV.2. The Heck Reaction (Alkene substitution via carbopalladation-dehydropal-ladation). J Wiley Interscience, New York... 

Intramolecular reactions with alkenes. While the intermolecular reaction is limited to unhindered alkenes, the intramolecular version permits the participation of even hindered substituted alkenes, and various cyclic compounds are prepared by the intramolecular Heck reaction. Particularly the... 

The best procedures for 3-vinylation or 3-arylation of the indole ring involve palladium intermediates. Vinylations can be done by Heck reactions starting with 3-halo or 3-sulfonyloxyindoles. Under the standard conditions the active catalyst is a Pd(0) species which reacts with the indole by oxidative addition. A major con.sideration is the stability of the 3-halo or 3-sulfonyloxyindoles and usually an EW substituent is required on nitrogen. The range of alkenes which have been used successfully is quite broad and includes examples with both ER and EW substituents. Examples are given in Table 11.3. An alkene which has received special attention is methyl a-acetamidoacrylate which is useful for introduction of the tryptophan side-chain. This reaction will be discussed further in Chapter 13. 

Heck reaction, palladium-catalyzed cross-coupling reactions between organohalides or triflates with olefins (72JOC2320), can take place inter- or intra-molecularly. It is a powerful carbon-carbon bond forming reaction for the preparation of alkenyl- and aryl-substituted alkenes in which only a catalytic amount of a palladium(O) complex is required. 

The regioselectivity of the addition of complex 4 to a substituted alkene is mainly influenced by steric factors. The substitution of hydrogen occurs preferentially at the carbon center which has the larger number of hydrogens. The Heck reaction... 

The Heck reaction is considered to be the best method for carbon-carbon bond formation by substitution of an olefinic proton. In general, yields are good to very good. Sterically demanding substituents, however, may reduce the reactivity of the alkene. Polar solvents, such as methanol, acetonitrile, N,N-dimethylformamide or hexamethylphosphoric triamide, are often used. Reaction temperatures range from 50 to 160 °C. There are various other important palladium-catalyzed reactions known where organopalladium complexes are employed however, these reactions must not be confused with the Heck reaction. 

An important virtue of the Heck reaction is that it can be applied with much success to essentially every type of olefin, although electron-deficient olefins are particularly well-suited. Moreover, the Heck reaction tolerates a variety of functional groups, and often does not require rigorous exclusion of oxygen and water.llb In fact, many alkene arylations proceed very efficiently in water.14... 

Larhed et al. investigated enantioselective Heck reactions with 2,3-dihydrofuran as alkene [86]. In the coupling with phenyl triflate, conditions previously reported by Pfaltz [87] were attempted under microwave irradiation. Interestingly, the catalytic system Pd2(dba)3/(4S)-4-t-butyl-2-[2-(diphenylphosphanyl)phenyl]-4,5-dihydro-l,3-oxazole, identified by the Swiss team, was found suitable for high-temperature microwave-assisted enantioselective Heck reactions (Scheme 76). Using a proton sponge as a base and benzene as a solvent gave the best conversions (Scheme 76). At tempera-... 

S)-N-methyl-2-vinyloxymethylpyrrolidine have also been used as an alkene partner in Heck reactions on vinyl triflates under microwave irradiation [91]. 

An interesting parallel was found while the microwave-enhanced Heck reaction was explored on the C-3 position of the pyrazinone system [29]. The additional problem here was caused by the capability of the alkene to undergo Diels-Alder reaction with the 2-azadiene system of the pyrazinone. An interesting competition between the Heck reaction and the Diels-Alder reaction has been noticed, while the outcome solely depended on the substrates and the catalyst system. Microwave irradiation of a mixture of pyrazinone (Re = H), ethyl acrylate (Y = COOEt) and Pd(dppf)Cl2 resulted in the formation of a mixture of the starting material together with the cycloaddition product in a 3 1 ratio (Scheme 15). On the contrary, when Pd(OAc)2 was used in combination with the bulky phosphine ligand 2-(di-t-butylphosphino)biphenyl [41-44], the Heck reaction product was obtained as the sole product. When a mixture of the pyrazinone (Re = Ar) with ethyl acrylate or styrene and Pd(dppf)Cl2 was irradiated at 150 °C for 15 min, both catalytic systems favored the Heck reaction product with no trace of Diels-Alder adduct. 

Arylation and Alkylation of Alkenes by Organopalladium Compounds The Heck Reaction... 

Unlike 14-18, the Heck reaction is not limited to activated substrates. The substrate can be a simple alkene, or it can contain a variety of functional groups, such as ester, ether,carboxyl, phenolic, or cyano groups. It can also be a... 

The Mizoroki-Heck reaction is a metal catalysed transformation that involves the reaction of a non-functionalised olefin with an aryl or alkenyl group to yield a more substituted aUcene [11,12]. The reaction mechanism is described as a sequence of oxidative addition of the catalytic active species to an aryl halide, coordination of the alkene and migratory insertion, P-hydride elimination, and final reductive elimination of the hydride, facilitated by a base, to regenerate the active species and complete the catalytic cycle (Scheme 6.5). 

This method ensures the deposition of very reactive metal nanoparticles that require no activation steps before use. We shall review here the following examples of catalytic reactions that are of interest in line chemical synthesis (a) the hydrogenation of substituted arenes, (b) the selective hydrogenation of a, 3-unsaturated carbonyl compounds, (c) the arylation of alkenes with aryl halides (Heck reaction). The efficiency and selectivity of commercial catalysts and of differently prepared nanosized metal systems will be compared. 

Studies on heterogeneous Pd metal catalysts for the arylation of alkenes with aryl halides (the Mirozoki-Heck reaction often reported as Heck reaction) [28] continue to... 

The Heck reaction consists in the Pd(0)-catalysed coupling of alkenes with an aryl or alkenyl halide or triflate in the presence of a base to form a substituted alkene (Scheme 7.1). The reaction is performed in the presence of an organopalladium catalyst. The halide or triflate is an aryl or a vinyl compound and the alkene contains at least one proton. 

Heck-type reactions 233-41 Heck reaction 233-5 Henry reactions 318-20, 321, 322 meso heterobicyclic alkenes, ring opening of 348-50 heterodonating ligands 9 heterodonor ligands with... 

Another important type of reactivity of palladium, namely oxidative addition to Pd(0), is the foundation for several methods of forming carbon-carbon bonds. Aryl126 and alkenyl127 halides react with alkenes in the presence of catalytic amounts of palladium to give net substitution of the halide by the alkenyl group. The reaction, known as the Heck reaction,128 is quite general and has been observed for simple alkenes, aryl-substituted alkenes, and substituted alkenes such as acrylate esters, vinyl ethers, and A-vinylamides.129... 

In aqueous DMF, the reaction can be applied to the formation of C-C bonds in a solid-phase synthesis with resin-bound iodobenzoates (Eq. 6.33).80 The reaction proceeds smoothly and leads to moderate to high yield of product under mild conditions. The optimal conditions involve the use of 9 1 mixture of DMF-water. Parsons investigated the viability of the aqueous Heck reactions under superheated conditions.81 A series of aromatic halides were coupled with styrenes under these conditions. The reaction proceeded to approximately the same degree at 400°C as at 260°C. Some 1,2-substituted alkanes can be used as alkene equivalents for the high-temperature Heck-type reaction in water.82... 

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