Cyclopentane Cyclopropane

Very recently, the first catalytic asymmetric intramolecular a-alkylation of an aldehyde has been achieved by the List group [70]. In the presence of a-methyl-substituted L-proline, (S)-61, as organocatalyst, ring-forming reactions leading to chiral cyclopentanes, cyclopropanes, and pyrrolidines proceed with high enantioselectivity - in the range 86-96% ee. Selected examples are shown in Scheme... 

In 2004, Vignola and List [111] demonstrated the ability of proline-derived catalysts to overcome drawbacks associated with the stoichiometric alkylation of preformed aldehyde enolates when they described an elegant amino acid catalyzed intramolecular a-alkylation reaction of haloaldehydes. The reaction furnished substituted cyclopentanes, cyclopropanes, and pyrrolidines in good yields and good enantio-selectivities (Scheme 8.23), when commercially available (5)-a-methyl proline (LV) as catalyst was used. The presence of a stoichiometric amount of additional base (tertiary amine) was required, not only to trap the hydrogen halide produced in the reaction but also because it has also significant effect on the stereoselectivity of the C—C bond-formation process by stabilizing the ant/ -TS of the /ra 5-enamine intermediate. Nevertheless, an intermolecular version of the reaction remains still elusive, mainly because of the deactivation of the amine catalyst by A -alkylation with the alkyl halide [112]. 

Complex 1 was found to activate a wide variety of hydrocarbons, including propane, pentane, cyclohexane, cyclopentane, methane, mesitylene, isobutene, and r-butylethylene [8, 9]. For linear hydrocarbons, a kinetic preference was observed for the exclusive activation of the C-H bonds of the terminal methyl groups. The activation of secondary C-H bonds was only observed when no other primary C-H bonds were available (e.g., cyclohexane, cyclopentane, cyclopropane [10]). With mesitylene, both aromatic and benzylic C-H bonds were cleaved. These observations were interpreted in terms of initial coordination of the hydrocarbon C-H bond to the 16-electron rhodium fragment, followed by rapid migration along the chain to... 

The hydrocarbons acetone, benzene, butene, cw-butene, cyclohexane, cyclopentane, cyclopropane, ethylene, isobutene, isooctane, methylcyclohexane, propylcyclohexane, neopentane, propyne, franj-hutene, and toluene. 

Some straightforward, efficient cyclopentanellation procedures were developed recently. Addition of a malonic ester anion to a cyclopropane-1,1-dicarboxylic ester followed by a Dieckmann condensation (S. Danishefsky, 1974) or addition of iJ-ketoester anions to a (l-phenylthiocyclopropyl)phosphonium cation followed by intramolecular Wittig reaction (J.P, Marino. 1975) produced cyclopentanones. Another procedure starts with a (2 + 21-cycloaddition of dichloroketene to alkenes followed by regioselective ring expansion with diazomethane. The resulting 2,2-dichlorocyclopentanones can be converted to a large variety of cyclopentane derivatives (A.E. Greene. 1979 J.-P. Deprds, 1980). 

At one time all cycloalkanes were believed to be planar It was expected that cyclopentane would be the least strained cycloalkane because the angles of a regular pentagon (108°) are closest to the tetrahedral angle of 109 5° Heats of combustion established that this is not so With the exception of cyclopropane the rings of all cycloalkanes are nonplanar... 

NBS can also be used to brominate alkanes. For example, cyclopropane, cyclopentane, and cyclohexane give the corresponding bromides when irradiated in a solution of NBS in dichloromethane. Under these conditions, the succinimidyl radical appears to be involved as the hydrogen-abstracting intermediate ... 

In addition to unsaturated fatty acids, several other modified fatty acids are found in nature. Microorganisms, for example, often contain branched-chain fatty acids, such as tuberculostearic acid (Figure 8.2). When these fatty acids are incorporated in membranes, the methyl group constitutes a local structural perturbation in a manner similar to the double bonds in unsaturated fatty acids (see Chapter 9). Some bacteria also synthesize fatty acids containing cyclic structures such as cyclopropane, cyclopropene, and even cyclopentane rings. 

Identify the lowest-energy conformer from among those provided cyclopropane, planar and puckered cyclobutane, planar and puckered cyclopentane and chair, half-chair, boat and twist-boat cyclohexane. (If... 

Physical properties of cycloalkanes [49, p. 284 50, p. 31] show reasonably gradual changes, but unlike most homologous series, different members exhibit different degrees of chemical reactivity. For example, cyclohexane is the least reactive member in this family, whereas both cyclopropane and cyclobutane are more reactive than cyclopentane. Thus, hydrocarbons containing cyclopentane and cyclohexane rings are quite abundant in nature. 

The data in Figure 4.3 show that Baeyer s theory is only partially correct. Cyclopropane and cyclobutane are indeed strained, just as predicted, but cyclopentane is more strained than predicted, and cyclohexane is strain-free. Cycloalkanes of intermediate size have only modest strain, and rings of 14 carbons or more are strain-free. Why is Baeyer s theory wrong ... 

Cyclopropane (115 kj/mol strain) and cyclobutane (110.4 kj/mol strain) have both angle strain and torsional strain. Cyclopentane is free of angle strain but has a substantial torsional strain due to its large number of eclipsing interactions. Both cyclobutane and cyclopentane pucker slightly away from planarity to relieve torsional strain. 

Conjugated chains, 14, 46 Correlation diagrams, 44, 50 Cyclobutadiene, 171 Cyclobutane, 47, 222 orbital ordering, 26 through-space interactions, 26 Walsh orbitals, 27 Cyclobutene, 200 Cyclohexane, 278 Cyclohexene (half-boat), 274 Cyclopen tadiene, 225 Cvclopen tadienone, 269 Cyclopentadienyl anion, 237 Cyclopentane, 254 Cyclopen ten e, 241 Cyclopropane, 41, 47, 153 construction of orbitals, 19, 22 Walsh orbitals, 22, 36, 37 Cyclopropanone, 48, 197 bond lengths, 38 Cyclopropen e, 49, 132 reactivity, 40... 

Cyclopentane, 1-cyano-l-phenyl-, 55, 94 Cyclopentane, methyl-, 55, 62, 112 Cyclopropane, 1-acetyl-1-phenyl-, 55, 94... 

Cyclohexene-l,4-dione, 2,3,5-tiichloro-3, 6-bis(l,l-dimethylethyl)- [5-Cyclo-hexcne-1,4-dione, 2,3,5-tnchloio-3,6-dwert-butyl-], 55, 33 Cyclopentadiene, 55, 15,16 Cyclopentane acetyl-,55,25 Cyclopentane 1-cyano-l-phenyl-, 55,94 Cyclopentane methyl-, 55, 62 Cyclopropane, 1-acetyl-l-phenyl-, 55 94... 

Investigation of Ethane, Propane, Isobutane, Neopentane, Cyclopropane, Cyclopentane, Cyclohexane, Allene, Ethylene, Isobutene, Tetramethylethylene, Mesitylene, and Hexamethylbenzene. Revised Values of Covalent Radii (by Linus Pauling and L. O. Brockway)... 

Fig. 3.—Radial distribution curves for (A) cyclopropane, (B) cyclopentane and (C) cyclohexane.

Cyclopropane, Cyclopentane, and Cyclohexane.—The sample of cyclopropane used was provided by Professor G. S. 

Fig. 4.—Theoretical intensity curves for cyclopropane, cyclopentane and cyclohexane.

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