Cycloalkanes reaction with activated

Introduction of the allene structure into cycloalkanes such as in 1,2-cyclononadiene (727) provides another approach to chiral cycloalkenes of sufficient enantiomeric stability. Although 127 has to be classified as an axial chiral compound like other C2-allenes it is included in this survey because of its obvious relation to ( )-cyclooctene as also can be seen from chemical correlations vide infra). Racemic 127 was resolved either through diastereomeric platinum complexes 143) or by ring enlargement via the dibromocarbene adduct 128 of optically active (J3)-cyclooctene (see 4.2) with methyllithium 143) — a method already used for the preparation of racemic 127. The first method afforded a product of 44 % enantiomeric purity whereas 127 obtained from ( )-cyclooctene had a rotation [a]D of 170-175°. The chirality of 127 was established by correlation with (+)(S)-( )-cyclooctene which in a stereoselective reaction with dibromocarbene afforded (—)-dibromo-trans-bicyclo[6.1 0]nonane 128) 144). Its absolute stereochemistry was determined by the Thyvoet-method as (1R, 87 ) and served as a key intermediate for the correlation with 727 ring expansion induced... 

In addition to enol silyl ethers, an optically active boryl enolate underwent the highly anri-stereoselective aldol reaction with a wide variety of aldehydes in the presence of TiCU (Eq. 34) [120]. The vinyl sulfides shown in Eq. (35) reacted with a,fi-unsaturated ketones via the 1,4-addition pathway in the presence of a titanium salt, but the reaction was followed by the cleavage of a carbon-carbon bond in the cycloalkane to give open chain products in a stereoselective manner [121]. The 1,2-type addition was observed, if the olefinie acetal was used instead of the corresponding carbonyl compound, as shown in Eq. (36) [121], The successive scission of the carbon-carbon bond took place analogously to give the same type of products as shown in Eq. (35). 

The preparation of allyltitanium compounds including those having functional groups is described by reaction of allylic halides or allylic alcohol derivatives with the system Ti(OPr1)4/MgXPr1 (X = C1, Br) (Scheme 7).24 Analogous allyltitanium complexes have also been reported by treatment of Ti(n) species with allylic alcohol derivatives, which proceeds via an oxidative addition pathway. Their reactions have been studied.25-27 These compounds are used to promote efficient syntheses of alkylidenecyclopropane and cycloalkane derivatives by regioselective reactions with carbonyl compounds,28,29 the stereoselective syntheses of optically active substituted piperidines and pyrrolidines... 

A recent synthesis of 11-deoxyanthracyclinones makes use of the ability of bromosulphones such as 75 to undergo annulation reactions with cycloalkan-ones which lack additional activating groups. Reductive desulphonylation and dehydration of the condensation product 77 gave 78 which was converted to ( )-7,ll-dideoxydaunomycinone 79 [65]. 

In metathesis polymerization, the catalyticaUy active species is a stable metal-carbene bond that is formed between the metal and the alkene. Upon reaction with cycloalkane, a living moiety capable of chain growth is formed. The olefin metathesis reaction mechanism is shown in Scheme 3.18. 

TABLE 5. Preexponentials (A) of the ozone reaction with cycloalkanes at 300 K calculated by the method of the activated complex. 

In a seminal contribution, C.-J. Li reported in 2007 the first iron-catalyzed CDC reaction between alkanes and activated methylene derivatives such as p-ketoesters or p-diketones. A simple FeCl2 catalytic system (20 mol%) can promote the coupling reaction in the presence of 2 equiv. of di-fert-butyl peroxide ( BuOO Bu) as the oxidant in an alkane as the solvent (Scheme 4.2). The CDC reaction is efficient with cycloalkanes and p-ketoesters (48-88% yields). It is worth mentioning that linear alkanes such as n-hexane produce moderate yields (42%) with a mixture of two regio-isomers in a 1.2 1 ratio. By contrast, the reaction with p-diketones is a more difficult task, and only low yields (10-15%) are obtained. 

Table XV summarizes kinetic parameters for hydrogenolysis reactions of alkanes and cycloalkanes over film catalysts and over supported catalysts for which it can be reasonably assumed that reaction is confined to the metallic phase. These kinetic parameters refer to the overall reaction, i.e., to the rate of disappearance of the parent molecule. It will be evident from Table XV that the catalytic activity of a given metal with a given...

In the case of iridium, complex [IrH2(PPh3)2(acetone)2] BF4 (11) was the first to carry out catalytically the dehydrogenation of cycloalkanes [13, 14]. However, it was later realized that the halocarbons used as solvents reacted with 11 to produce the stable species [HL2lr(p-Cl)2(. i-X)IrL2H]BF4 (X = Cl (14) or H (15)) [16] (Scheme 13.8), and that elimination of the solvent by running the reactions in neat alkane not only improved yields but also permitted the activation of other previously unreactive cycloalkanes, such as methyl- and ethyl-cyclopentane. However, it was also noted that the system in some cases was not catalytic, due mainly to decomposition of the catalyst at the temperatures employed [16]. 

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... 

Italogenation catalyst. Chromium carbonyl catalyzes the monohalogenation of cyclohexane by CC14 (78% yield). Other cycloalkanes undergo the same reaction, liioniination can be effected in this way with CBrCl,. Other metal carbonyl complexes arc less active. Cr(CO)f, is actually more efficient than di-/-butyl peroxide. A free indical mechanism is involved. 

Fig. 8.12 The molecular orbitals of 1,5-pentanediyl and cyclopentane, relevant to the C-C cleavage of the cycloalkane that leads to the acyclic diradical. Calculated with the HF/STO-3G wavefunction and localized by the NBO method. The cyclopentane C-C bonding orbital, MO 10, relevant to this reaction, must be switched with MO 20, a pure C-H bonding MO with no relevance here, to move the C-C MO into the active space. Note that these molecules have 40 electrons...

Electron-transfer reactions of higher cycloalkanes were also studied. Electron transfer from C-C7H14 to unstable holes generated by radiolysis in Freon-113 gave rise to a stable radical cation, c-Ci A f its spectrum was interpreted in terms of a twisted chair form with C2 symmetry [37]. Finally, radiolysis of c-CgHie in a Freon-113 matrix generated a Jahn-Teller-active radical cation, c-CgHie, with three sets of non-equivalent protons [37]. A detailed discussion of these species exceeds the scope of this review. 

It is fairly apparent that encapsulation of the RuFiePc complex in NaX dramatically alters the catalytic activity and selectivity, however, that in itself is not evidence for the intrazeolite location of the complex. Therefore, we examined the oxidation of the much larger cyclododecane using the same reaction conditions as for cyclohexane. We found the homogeneous RuFisPc catalyst had virtually no preference for either cycloalkane, showing approximately the same number of turnovers per day. In contrast, the RuFiePc-NaX catalyst exhibited relatively low activity ( 300 tumovers/day) for the larger cyclododecane. The acti dty of the zeolite encapsulated complex was nearly 10 times greater for the smaller cyclohexane. This shape selectivity is consistent with the active sites located inside the zeolite. 

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