Organic halides alkenes

With a combination of organic halide, alkene or alkyne, and palladium catalyst, the reaction may take a superficially similar, but different pathway other than a Heck-type reaction. In these, the halogen is retained in the products, as an alkyl or vinyl halide. These results occur when the starting organic halide is allyl, a- to a carbonyl or similar group, or attached to a perhalogenated carbon atom. In much of the early work, mixtures with Hecklike elimination products were obtained, due to elimination caused by the presence of amine bases in the reaction mixture (equation 165)323. 

Several Pd(0) complexes are effective catalysts of a variety of reactions, and these catalytic reactions are particularly useful because they are catalytic without adding other oxidants and proceed with catalytic amounts of expensive Pd compounds. These reactions are treated in this chapter. Among many substrates used for the catalytic reactions, organic halides and allylic esters are two of the most widely used, and they undergo facile oxidative additions to Pd(0) to form complexes which have o-Pd—C bonds. These intermediate complexes undergo several different transformations. Regeneration of Pd(0) species in the final step makes the reaction catalytic. These reactions of organic halides except allylic halides are treated in Section 1 and the reactions of various allylic compounds are surveyed in Section 2. Catalytic reactions of dienes, alkynes. and alkenes are treated in other sections. These reactions offer unique methods for carbon-carbon bond formation, which are impossible by other means. 

In Grignard reactions, Mg(0) metal reacts with organic halides of. sp carbons (alkyl halides) more easily than halides of sp carbons (aryl and alkenyl halides). On the other hand. Pd(0) complexes react more easily with halides of carbons. In other words, alkenyl and aryl halides undergo facile oxidative additions to Pd(0) to form complexes 1 which have a Pd—C tr-bond as an initial step. Then mainly two transformations of these intermediate complexes are possible insertion and transmetallation. Unsaturated compounds such as alkenes. conjugated dienes, alkynes, and CO insert into the Pd—C bond. The final step of the reactions is reductive elimination or elimination of /J-hydro-gen. At the same time, the Pd(0) catalytic species is regenerated to start a new catalytic cycle. The transmetallation takes place with organometallic compounds of Li, Mg, Zn, B, Al, Sn, Si, Hg, etc., and the reaction terminates by reductive elimination. 

Acyl halides are intermediates of the carbonylations of alkenes and organic-halides. Decarbonylation of acyl halides as a reversible process of the carbo-nylation is possible with Pd catalyst. The decarbonylation of aliphatic acid chlorides proceeds with Pd(0) catalyst, such as Pd on carbon or PdC, at around 200 °C[109,753]. The product is a mixture of isomeric internal alkenes. For example, when decanoyl chloride is heated with PdCF at 200 C in a distillation flask, rapid evolution of CO and HCl stops after I h, during which time a mixture of nonene isomers was distilled off in a high yield. The decarbonylation of phenylpropionyl chloride (883) affords styrene (53%). In addition, l,5-diphenyl-l-penten-3-one (884) is obtained as a byproduct (10%). formed by the insertion of styrene into the acyl chloride. Formation of the latter supports the formation of acylpalladium species as an intermediate of the decarbonylation. Decarbonylation of the benzoyl chloride 885 can be carried out in good yields at 360 with Pd on carbon as a catalyst, yielding the aryl chloride 886[754]. 

Oxidative reactions of alkenes with Pd(II) are treated in Chapter 3,. Section 2, catalytic reactions of alkenes with organic halides are discussed in this chapter. Section 1.1, and other catalytic reactions of alkenes are discussed in this section. 

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

The elimination of hydrogen halide from organic halides under basic conditions generates alkenes and is a fundamental reaction in organic chemistry. It is sometimes carried out with a base in aqueous media.14 In contrast, the corresponding Hofmann-type eliminations of quaternary ammonium hydroxides are frequently carried out in aqueous media,15 which will be covered in Chapter 11. 

Olefinations using a solid-supported triphenylphosphine were accomplished within 5 min of microwave heating at 150 °C using potassium carbonate as the base and methanol as the solvent (Scheme 7.96). A variety of aldehydes and organic halides were studied with the solid-supported phosphine, yielding the corresponding alkenes in excellent purities. 

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). 

The dehalogenation of organic halides by organotin hydrides takes place in most cases with a free-radical mechanism [1, 84, 85], The stereospecific reduction of 1,1-dibromo-l-alkenes with Bu3SnH discovered by Uenishi and coworkers [86-89], however, did not occur in the absence of palladium complexes and did not involve radicals. For the synthesis of (Z)-l-bromo-l-alkenes, [(PPh3)4Pd] proved to be the most effective catalyst which could also be generated in situ. The reaction in Eq. (7) proceeded at room temperature and a wide range of solvents could be used. 

If one wants to use only a metal halide as the initiator for an alkene polymerisation, an analysis similar to ours can be made for the metal halide alone. In addition, there is a 1 2 equilibrium for the organic halide [35, 36] and a molecular aggregate <-> single molecule equilibrium associated with the metal halide. Thus, a solution of a carbocation salt is more exactly described by the series of linked equilibria summarised in Scheme 5. 

Vinylation or arylation of alkenes with the aid of a palladium catalysts is known as the Heck reaction. The reaction is thought to proceed through the oxidative addition of an organic halide, RX onto a zero-valent [PdL2] species followed by coordination of the olefin, migratory insertion of R, reductive elimination of the coupled product and dehydrohalogenation of the intermediate [HPdXL2] (Scheme 6.1). 

An early example of a dendritie eatalyst was reported by Knapen et al. 24), who functionalized GO (generation zero) and G1 earbosilane dendrimers with up to 12 NCN pincer-nickel(II) groups (7a). These dendrimers were applied as eatalysts in the Kharasch addition of organic halides to alkenes (Seheme 3). 

Braese, S. de Meijere, A. Gross-Coupling of Organic Halides with Alkenes the Heck Reaction. In Metal-Catalyzed Cross-Coupling Reactions, 2nd ed. de Meijere, A., Diederich, F., Eds. Wiley-VCH Weinheim, 2004 pp 217-315. 

The reaction of the organic halide with magnesium is carried out in a non-protic polar solvent, usually diethyl ether or THF. Typical by-products are RR, RH and R(-H) (alkene), resulting from coupling and disproportionation reactions of the organic moiety. Also, by-products resulting from solvent attack are sometimes formed, but usually to a lesser extent. 

Titanocene dichloride also catalyzes a regioselective carbomagnesiation of alkenes 187 (equation 115) and dienes 188 (equation 116). The reaction proceeds at 0°C in THF in the presence of Cp2TiCl2, an organic halide and n-BuMgCl which leads to the catalytic species, affording benzyl, allyl or a-silyl alkylmagnesium halides, which are trapped with electrophiles (equation 117) . ... 

Tetrabutylammonium(triphenylsilyl)difluorosilicate is a new fluoride source soluble in anhydrous, nonhygroscopic and neutral organic solvents. This reagent converts organic halides and sulfonates into fluorides, however, 4-6 equivalents are required. 1-Iodooctane is converted to 1-fluorooctane (33) in 74% yield, the rest (26%) being the alkene.221 Apparently with tetra-alkylammonium fluorides, the formation of alkenes is generally not completely suppressable. 

The reaction of heterocyclic lithium derivatives with organic halides to form a C-C bond has been discussed in Section 3.3.3.8.2. This cannot, however, be extended to aryl, alkenyl or heteroaryl halides in which the halogen is attached to an sp2 carbon. Such cross-coupling can be successfully achieved by nickel or palladium-catalyzed reaction of the unsaturated organohalide with a suitable heterocyclic metal derivative. The metal is usually zinc, magnesium, boron or tin occasionally lithium, mercury, copper, and silicon derivatives of thiophene have also found application in such reactions. In addition to this type, the Pd-catalyzed reaction of halogenated heterocycles with suitable alkenes and alkynes, usually referred to as the Heck reaction, is also discussed in this section. 

In the early days of organic chemistry, alkenes were described as unsaturated because, in contrast to the saturated alkanes, they were found to react readily with substances such as halogens, hydrogen halides, oxidizing agents, and so on. Therefore, the chemical affinity of alkenes was regarded as unsatisfied or unsaturated. (Also see Section 1-11.)... 

Reviews are available on the palladium-catalyzed carbonylation of organic halides,554 dienes555 and mixtures of alkenes and organic halides.556... 

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