Cyclopentane, from cyclohexene

Cyclopentene-l-carboxaldehydes are obtained from cyclohexene precursors by the sequence cyclohexene - cyclohexane-1,2-diol -> open-chain dialdehyde - cyclopentane aldol. The main advantage of this ring contraction procedure is, that the regio-and stereoselectivity of the Diels-Alder synthesis of cyclohexene derivatives can be transferred to cyclopentane synthesis (G. Stork, 1953 G. BUchi, 1968). 

Likewise it is possible to differentiate between substituted and unsubstituted alicycles using inclusion formation with 47 and 48 only the unbranched hydrocarbons are accommodated into the crystal lattices of 47 and 48 (e.g. separation of cyclohexane from methylcyclohexane, or of cyclopentane from methylcyclopentane). This holds also for cycloalkenes (cf. cyclohexene/methylcyclohexene), but not for benzene and its derivatives. Yet, in the latter case no arbitrary number of substituents (methyl groups) and nor any position of the attached substituents at the aromatic nucleus is tolerated on inclusion formation with 46, 47, and 48, dependent on the host molecule (Tables 7 and 8). This opens interesting separation procedures for analytical purposes, for instance the distinction between benzene and toluene or in the field of the isomeric xylenes. 

Trans-1 -allyl-2-(trimethylsilyl)cyclopentane and trans-1 -allyl-2-(trimethylsilyl)-cyclohexane are formed from the reaction of la with cyclopentene and cyclohexene, respectively. A second allylsilylation reaction of these compounds with la also gives unusual allylsilylation products, 7-cyclopent-l-enyl-2,2-dimethyl-4-(trimethylsilyl-methyl)-2-silaheptane (30%) and 4-((cyclohex-l-enyl)methyl)-2,2,8,8-tetramethyl-2,8-disilanonane (39%). As observed in the allylsilylation of 4-(trimethylsilyl-methyl)-l-alkenes, these products are likely formed via intramolecular silyl rearrangements. In this case, the results strongly suggest that a 1,5-silyl shift and... 

Goda et al. (1995) separated capsanthin esters from oleoresin of paprika fruits from Spain and determined their chemical structures without saponification. The major monoesterified capsanthin was identified as 3 -0-myristoylcapsanthin. It is suggested that the rate of esterification of fatty acid to the hydroxyl group on the cyclopentane ring of capsanthin is different to that on the cyclohexene ring. 

Petrov and Shchekin (297) showed that below the cracking temperature (250-316°C.) cyclohexene undergoes over silica-alumina hydrogen disproportionation and dimerization. Identical results were obtained from 1-methyl-l-cyclopentene. Ring expansion of lower alkylated cyclopentanes occurs simultaneously with polymerization. However, no bicyclic compounds with similar rings were formed. 

When dehydrogenation was carried out in a stream of hydrogen at 325°C, the yield of aromatic hydrocarbons formed in the dehydrogenation of cyclohexane and cyclohexene derivatives was 87—99%. As a result of side-reactions an insignificant amount of dealkylation products (benzene, toluene) was also formed. Decalin was most difficult to dehydrogenate, and in this instance, together with naphthalene, tetralin was also formed. Under these conditions isomerization of cyclopentane derivatives into cyclohexane hydrocarbons did not take place, and aromatic hydrocarbons were not formed from cyclopentane hydrocarbons. The process, however, was complicated by hydrocracking reactions. 

COMPARISON OF THE RATIOS OF THE RATE coefficients OF ELIMINATION FROM CIS AND trcinS ISOMERS IN THE CYCLOHEXENE AND CYCLOPENTANE SYSTEMS... 

The heat of hydrogenation is a measure of the difference between the chemical bonding energy in the unsaturated and saturated cyclic compounds, so that to make a useful comparison between c3 clopentene and cyclohexene allowance must be made, in the heat of hydrogenation of cyclopentene, for the strain which appears in cyclopentane, but not in cyclohexane. This strain energy of 6 0 kcal/mole has been evaluated from a comparison of the heats of combustion of the cycloalkanes with the higher, normal straight-chain alkanes. 

It is of interest to show that the experimental data points of many organic compounds from other families (especially liquids) closely fit the correlation defined by Eq. (20). The log values of low molecular weight alcohols are about 0.2-0.4 unit higher than values calculated from their solubilities by Eq. (20). Hexachloro-1,3-butadiene with log = 4.90 and log S = -5.01 (20) and other alkylhalides (44) are well represented by the above correlation. Similarly, the measured log A ow values of pentane, cyclopentane, cyclohexane, and cyclohexene (66) are in close agreement with values estimated from their sol-ubiliti (44), Lindane, with a solubility of 7.8 ppm at 25T (108), = 386 K,... 

Cyclopentene reacts exclusively to give cyclopentane carboxylic acid. Formation of methyl-substituted four-membered rings has not been observed. Also cyclohexene reacts to give nearly 90 % of cyclohexane carboxylic acid, whereas cycloolefins containing 8, 9 and 10 C-atoms in the ring generally do not form secondary acids. The performance of the methyl-substituted cycloalkenes can be seen from fig. 18. 

The unsaturated fatty acids are also transformed, via the radicals formed during heating to higher temperatures (e.g. during frying), into cyclic fatty acids with five- and six-membered rings. Cyclic acids derived from oleic acids are saturated compounds. The products formed from linoleic acid have one double bond. These products include cyclopentene acids and cyclopentane and cyclohexane acids with one cis double bond in the side chain. Linolenic acid forms products with two double bonds, such as cyclopentene and cyclohexene acids with one cis double bond in the side chain. 

In addition to the cyclic dimers of the cyclohexene type, some cyclic cyclopentane C-C dimers and acycKc C-C dimers may also be formed. The mechanism of their formation (Figure 3.21) is demonstrated for reactions of one of the four main free radicals generated from oleic acid. An acycUc dimer forms by recombination of two radicals (reaction A in Figure 3.21), but also by addition of a radical to the double bond of another radical (reactions B... 

The product distribution depends on the nickel-phosphine ratio and the best yield of A (70% cis/trans = 19/1) is obtained when bisdiene is treated in toluene at 60 °C with llmol% Ni(COD)2 and 33mol% PhjP [124]. When a phosphite ligand is used, cyclohexene B or cyclopentane C derivatives are the major products. Functional groups such as esters, ketones, or ethers remain intact under the reaction conditions. The reaction is stereoselective and has been used for the synthesis of polycyclic natural products [125-128]. For example, the key intermediate for the enantioselective synthesis (-H)-asteriscanolide is obtained from a similar synthetic route [128]. The use of this strategy for the construction of a taxan skeleton has been briefly explored [129]. 

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