Methylcyclopentane alkylation

The second termination reaction is alkyl chain end transfer from the active species to aluminium [155]. This termination becomes major one at lower temperatures in the catalyst systems activated by MAO. XH and 13CNMR analysis of the polymer obtained by the cyclopolymerization of 1,5-hexadiene, catalyzed by Cp ZrCl2/MAO, afforded signals due to methylenecyclopentane, cyclopentane, and methylcyclopentane end groups upon acidic hydrolysis, indicating that chain transfer occurs both by /Miydrogen elimination and chain transfer to aluminium in the ratio of 2 8, and the latter process is predominant when the polymerization is carried out at — 25°C [156]. The values of rate constants for Cp2ZrCl2/MAO at 70°C are reported to be kp = 168-1670 (Ms) 1, kfr = 0.021 - 0.81 s 1, and kfr = 0.28 s-1 [155]. 

Aluminum chloride, used either as a stoichiometric reagent or as a catalyst with gaseous hydrogen chloride, may be used to promote silane reductions of secondary alkyl alcohols that otherwise resist reduction by the action of weaker acids.136 For example, cyclohexanol is not reduced by organosilicon hydrides in the presence of trifluoroacetic acid in dichloromethane, presumably because of the relative instability and difficult formation of the secondary cyclohexyl carbocation. By contrast, treatment of cyclohexanol with an excess of hydrogen chloride gas in the presence of a three-to-four-fold excess of triethylsilane and 1.5 equivalents of aluminum chloride in anhydrous dichloromethane produces 70% of cyclohexane and 7% of methylcyclopentane after a reaction time of 3.5 hours at... 

None of the 3-methylpentene isomers formed more methylcyclopentane than did 3-methylpentane. With the alkene-alkyl insertion mechanism the reverse should be expected, especially for 3-methyl-l-pentene. 

Cycloalkanes possessing a tertiary carbon atom may be alkylated under conditions similar to those applied for the alkylation of isoalkanes. Methylcyclopentane and methylcyclohexane were studied most.5 Methylcyclopentane reacts with propylene and isobutylene in the presence of HF (23-25°C), and methylcyclohexane can also be reacted with isobutylene and 2-butene under the same conditions.20 Methylcyclopentane is alkylated with propylene in the presence of HBr—AlBr3 (—42°C) to produce l-ethyl-2-methylcyclohexane.21 C12H22 bicyclic compounds are also formed under alkylation conditions.21 22 Cyclohexane, in contrast, requires elevated temperature, and only strong catalysts are effective. HC1—AICI3 catalyzes the cyclohexane-ethylene reaction at 50-60°C to yield mainly dimethyl- and tetra-methylcyclohexanes (rather than mono- and diethylcyclohexanes). The relatively weak boron trifluoride, in turn, is not active in the alkylation of cyclohexane.23... 

One of these initiator radicals should react with methylcyclopentane to give a free-radical version of methylcyclopentane. As we have seen, a bromine or chlorine radical can abstract a hydrogen atom from an alkane to generate an alkyl radical. The bromine radical is highly selective, and the most stable alkyl radical should result. Abstraction of the tertiary hydrogen atom gives a tertiary radical. 

Cyclic 1,2-diketones, such as3-methylcyclopentane-l,2-dione, act as oxygen nucleophiles in palladium(0)-catalyzed reactions with a range of cyclic and acyclic allylic esters. The products of these reactions were subjected to a lanthanide-catalyzed Claisen rearrangement to access the C-alkylated products. 

In a study of the reaetion between alkyl halides and the electrogenerated naphthalene radical anion, Sease and Reed [297] observed that only alkyl chlorides, such as 1-chloro-hexane and 6-chloro-l-hexene, are catalytically reduced 1-chlorohexane gives only n-hex-ane, whereas 6-chloro-l-hexene affords methylcyclopentane and 1-hexene. In an earlier paper [296], the reactions of 1-bromo- and 1-chlorobutane with the electrogenerated radical anions of rmn -stilbene and anthracene in DMSO were examined. Britton and Fry [298] elucidated the kinetics of the electron-transfer reaction between 1-chlorooctane and the phenanthrene radieal anion in DMF. 

Indeed the carbene-alkyl insertion mechanism in Scheme 45 neatly explains why the rates of dehydrocyclization of 1, 2, and 3 are so similar. However, since 2-methylhexane also undergoes 1-5 dehydrocyclization, involvement of methylenic carbon atoms and not simply terminal carbon atoms must also be possible. The pathway for the C7-alkanes must be the reverse of nonselective hydrogenolysis of methylcyclopentane (Mechanism A), since it also results in isomerization to 2,4-dimethylpentane and 3-methylhexane, most likely via adsorbed 1,3-dimethylcyclopentane (scheme 46). It is... 

D.1. Reactions with Nucleophiles. Previously, a jr-allylic palladium complex was generated by reaction of palladium reagents with allylic hydrocarbons prior to reaction with nucleophiles. In the catalytic version of this reaction, an allylic halide or an allylic acetate is used with a palladium(O) reagent. Why use a palladium complex when enolate alkylation is a well-known process (sec. 9.3.A) A typical enolate coupling reaction is the conversion of 2-methylcyclopentane-l,3-dione (373) to the enolate anion by reaction with NaOH, allowing reaction with allyl bromide. Under these conditions only 34% of 374 was obtained. When allyl acetate was used in place of allyl bromide in this reaction and tetra w(triphenylphosphino)palladium was used as a catalyst, a 94% yield of 374 was obtained.224 in this reaction, formation of the Jt-allyl palladium complex facilitated coupling with the nucleophilic enolate derived from 373, which exhibited poor reactivity in the normal enolate alkylation sequence. 

Metal cations Metal cation reduction Metal cations in MeAPO synthesis Metal corrosion prevention Metallocene, supported catalyst 24-0-05 Metallosilicates, microporous Methanol adsorption Methanol amination Methanol conversion Methanol dehydrogenation Methanol formation Methanol in alkylation 15-0-03 25-0-03 Methanol to hydrocarbons Methanol, reagent Methanol, steam reforming Methylamine in MFI synthesis N-Methylation, aniline Methylation, 4-methylbiphenyl Methylation, toluene, model 4-methylbiphenyl, methylation Methylcyclohexane cracking Methylcyclopentane hydroconversion Methylene silanes... 

Insertion into C-H bonds is more probable than insertion into C-C bonds. Insertion into C-C bonds does not appear to occur at all. For example, photolysis of diazomethane in cyclopentane at —75 °C produced only methylcyclopentane, with cyclohexane not being observed. Singlet carbenes are thought to add to C- H bonds by a concerted process, while triplet carbenes can produce net addition through hydrogen abstraction and then recombination of the alkyl radicals. It was found that o-(2-endo-norbornyl)phenylcarbene inserts into the 3-position in such a way as to give a trans-junction (Scheme 5.47). 

The reaction is stereospecific the alkyl group migrates with retention of configuration, as illustrated for the oxidation of c/5-l-acetyl-2-methylcyclopentane only the cis product is obtained. 

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