Alkenes conjugate reactions

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. 

Our discussion of chemical reactions of alkadienes will be limited to those of conjugated dienes. The reactions of isolated dienes are essentially the same as those of individual alkenes. The reactions of cumulated dienes are—like their preparation— so specialized that their treatment is better suited to an advanced course in organic chemistry. 

Conjugated nitroso alkenes in reactions with heterocycles 98UK523. 

Enamines react with acceptor-substituted alkenes (Michael acceptors) in a conjugate addition reaction for example with o ,/3-unsaturated carbonyl compounds or nitriles such as acrylonitrile 8. With respect to the acceptor-substituted alkene the reaction is similar to a Michael addition ... 

Nenajdenko et al. described the first example of addition of a 1,2-dication to C-C mutiple bonds. The only S-S dication found to participate in this reaction was the highly strained dication 115 derived from 1,4-dithiane. The reaction with alkenes 119 proceeded under mild conditions and led to derivatives of dithioniabicyclo[2.2.2]octane 120 as shown in Equation (33) and Table 21 <1998JOC2168>. This reaction was sensitive to steric factors and proceeded only with mono and 1,2-disubstituted ethylenes. Only alkenes conjugated with aromatic or cyclopropane moieties underwent this reaction. For the 1,2-disubstituted alkenes used in this study, the relative configuration of substitutents at the double bond was preserved and only one diastereomer was formed (see entries 2 and 3). 

Reaction with alkenes is sensitive to steric factors - in the case of dication 49, only reaction with mono- and 1,2-disubstituted ethylenes afforded identifiable reaction products. Only alkenes conjugated with aromatic or cyclopropane moiety undergo this reaction. In the case of 1,2-disubstituted alkenes, the relative configuration of substitutents at the double bond is preserved and only one diastereomer is formed. 

In total, over the past six years, the chelating P,N-ligands have shown considerable promise in a variety of enantioselective processes, including transfer-hydrogenation and hydrosilylation of ketones, hydroboration of alkenes, conjugate addition to enones and Lewis-acid catalysed Diels-Alder reactions, in addition to those described above.128,341 It is anticipated that this list will continue to grow, and... 

Tetraalkylammonium bromide was found to be a good catalyst for the conjugate addition of thiols to a,p-unsaturated nitriles, carboxylic esters, ketones, aldehydes, and nitro alkenes. The reactions proceeded rapidly and gave high yields of products (typically, 90%) (160). 

Some interesting new chemistry has been produced on the well-known 1,5-electrocyclization reaction of alkene-conjugated nitrile ylides but the greatest... 

Very little work has been done on reactions involving nucleophiles formed from hydrocarbons.124-142 The limitation on basicity of the carbanion, so that it does not react with solvent, has led to use of conjugated hydrocaibons, such as dienes or alkenes conjugated with aromatic rings. When initiated by dissolving alkali metal in liquid ammonia, complex mixtures are often produced on account of reduction processes,124 and regiochemistry and multiplicity of arylation in conjugated systems also create prob-... 

Stabilized ylids, that is ylids whose anion is stabilized by further conjugation, usually within a carbonyl group, give E-alkenes on reaction with aldehydes. These ylids are also enolates and were discussed in Chapter 27. 

CO)2Fe (THF) BFT A transition state model for the syn stereoselective cyclo-propanations of alkenes with diazoacetic ester by Rh-porphyrin catalysts has been proposed. Alkenes , conjugated dienes and enol ethers are stereoselectively cyclopropanated with Rh(II) -stabilized 1- (alkoxycarbonyl)vinyl carbenoids derived from the diazo precursors and Rh2(OAc)4 (equation 95). The Cu(acac)2-catalyzed reactions of Me3SiCH2COCHN2 with alkenes provide the expected adducts in good yields ". ... 

The cyclopropanation of alkenes with dihalocarbenes, CX2 or CX X, except for CF2, can be efficiently executed by the PTC procedures (CHX3/strong aqueous base/catalyst), which are well-documented in books and reviews . The dichloro- and dibromo-carbene additions by the PTC procedure have successfully been applied for many alkenes, conjugated polyolefins and allenes. Satisfactory results are also reported for the reactions of sterically hindered olefins as well as electronically deactivated olefins, which frequently... 

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