Alkenes electrophile reactions with

The next step is merely a repeat instead of an electrophilic reaction with a proton, we have an electrophilic reaction with a carbocation. The reasoning is the same we get the tertiary carbocation intermediate. What then follows is loss of a proton to give an alkene, and there are two possible products, depending upon which proton is released. Both products are formed, though we would expect the more-substituted alkene to predominate. We are not asked for, or given, any information about product ratios. 

A second type of organopalladium intermediates are 7r-allyl complexes. These complexes can be obtained from Pd(II) salts and allylic acetates and other compounds with potential leaving groups in an allylic position.79 The same type of 7i-allyl complexes can be prepared from alkenes by reaction with PdCl2 or Pd(02CCF3)2.80 The reaction occurs by electrophilic attack on the n electrons followed by loss of a proton. The proton loss probably proceeds via an unstable species in which the hydrogen is bound to... 

The effect of monofluorination on alkene or aromatic reactivity toward electrophiles is more difficult to predict Although a-fluonne stabilizes a carbocation relative to hydrogen, its opposing inductive effect makes olefins and aromatics more electron deficient. Fluorine therefore is activating only for electrophilic reactions with very late transition states where its resonance stabilization is maximized The faster rate of addition of trifluoroacetic acid and sulfuric acid to 2-fluoropropene vs propene is an example [775,116], but cases of such enhanced fluoroalkene reactivity in solution are quite rare [127] By contrast, there are many examples where the ortho-para-dueeting fluorine substituent is also activating in electrophilic aromatic substitutions [128]... 

Thus, with electron-rich or electron-poor monosubstituted alkenes, the reaction with tri-fluoroacetonitrile oxide is more regioselective than with benzonitrile oxides. and the oxygen of the nitrile oxide adds to the substituted carbon. With other dipolarophiles, cyeloaddition is less regioselective. Competitive reactions include an electrophilic addition on the nitrile oxide, in particular with 1,1-disubstituted alkenes. and a further cyeloaddition which can occur when the dipolarophile is used in excess. ... 

Returning to a reaction we met right at the start of this chapter will illustrate that the regio-and stereochemistry of many different electrophilic reactions with alkenes can be controlled by intramolecular nucleophiles. The mercuration of the cis alkene Z-184 leads to a 6 1 ratio of diastereoisomers of a cyclic ether 185 by a related trapping of the intermediate by the internal OH group. 

Metallated alkenes such as alkenyllithium or Grignard species undergo addition reactions with various electrophiles. Reaction with primary alkyl bromides or iodides is possible. Wurtz self-coupled products can be avoided if the alkenyllithium species is generated by tin-lithium exchange, or by insertion of lithium metal into... 

Organoaluminum reagents also undergo a variety of synthetically useful reactions with alkynes. The addition of dialkylaluminum hydrides to alkynes is a stereospecific cis addition. Vinylalanes that are capable of being converted to substituted alkenes by reaction with electrophilic reagents are formed. 

In the laboratory, alkenes are often hydrated by the oxymercuration-demercuration procedure. Oxymercuration involves electrophilic addition of Hg2+ to the alkene on reaction with mercury(II) acetate [(CH3C02)2Hg, often abbreviated Hg(OAc)2] in aqueous tetrahydrofuran (THF) solvent. When the intermediate organomercury compound is then treated with sodium borohydride, NaBH4, demercuration occurs to produce an alcohol. For example ... 

Pd(II) compounds coordinate to alkenes to form rr-complexes. Roughly, a decrease in the electron density of alkenes by coordination to electrophilic Pd(II) permits attack by various nucleophiles on the coordinated alkenes. In contrast, electrophilic attack is commonly observed with uncomplexed alkenes. The attack of nucleophiles with concomitant formation of a carbon-palladium r-bond 1 is called the palladation of alkenes. This reaction is similar to the mercuration reaction. However, unlike the mercuration products, which are stable and isolable, the product 1 of the palladation is usually unstable and undergoes rapid decomposition. The palladation reaction is followed by two reactions. The elimination of H—Pd—Cl from 1 to form vinyl compounds 2 is one reaction path, resulting in nucleophilic substitution of the olefinic proton. When the displacement of the Pd in 1 with another nucleophile takes place, the nucleophilic addition of alkenes occurs to give 3. Depending on the reactants and conditions, either nucleophilic substitution of alkenes or nucleophilic addition to alkenes takes place. 

Ozone IS a powerful electrophile and undergoes a remarkable reaction with alkenes m... 

The double bond m the alkenyl side chain undergoes addition reactions that are typical of alkenes when treated with electrophilic reagents... 

The stabilization of chloromethoxycarbene (234) was intensively studied. It is formed from diazirine (233) in a first order reaction with fi/2 = 34h at 20 C. It reacts either as a nucleophile, adding to electron poor alkenes like acrylonitrile with cyclopropanation, or as an electrophile, giving diphenylcyclopropenone with the electron rich diphenylacetylene. In the absence of reaction partners (234) decomposes to carbon monoxide and methyl chloride (78TL1931, 1935). 

With very electrophilic olefins, an alternative hydrogen fluoride addition process is often preferred This process, involving reaction of the olefin with fluoride ion in the presence of a proton donor, is applicable to certain perhalogen ated alkenes [/] and substrates with other electron attracting groups attached to the double bond [i5, 36] (equations 4 and 5)... 

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