Cyclopentane ring system

SCHEME 4. Some natural long-chain acids with a cyclopentane ring system. 

Iridoids (Loganin and Secologanin). The relatively small group of richly oxidized terpenes resulting from a cycUzation giving rise to a fused pyran-cyclopentane ring system is widely known as iridoids. All of those isolated so far have a ds-fused... 

Assemble a model of norbornane (bicyclo[2.2.1]heptane). Observe the two cyclopentane ring systems in the molecule. The structure may also be viewed as having a methylene (CH2) bridge between carbon atoms 1 and 4 of cyclohexane. Describe the conformation of the cyclohexane ring system in norbornane. How many eclipsing interactions are present ... 

Hydrosilylation of 1,6-dienes accompanied by cyclization giving a five-membered ring system is emerging as a potential route to the synthesis of functionalized carbocycles.81,81a,81b 82 As its asymmetric version, diallylmalonates 86 were treated with trialkylsilane in the presence of a cationic palladium catalyst 88, which is coordinated with a chiral pyridine-oxazoline ligand. As the cyclization-hydrosilylation products, //ww-disubstituted cyclopentanes 87 were obtained with high diastereoselectivity (>95%), whose enantioselectivity ranged between 87% and 90% (Scheme 25).83 83a... 

In contrast, the so-called bis-nor-Wieland-Miescher ketone (2) is a more complex synthetic problem, since the molecule is a multidissonant system with two dissonant bifunctional group relationships (1,4-D and 1,6-D) and two dissonant cyclopentane rings, besides a 1,5-consonant bifunctional group relationship. Its synthesis was only accomplished 30 years after the synthesis of its consonant homologue [5],... 

Naphthenic Acids Acids derived from crude oil which are usually monocarboxylic, monocyclic, and completely saturated. Many are derivatives of cyclopentane and more complex alicyclic ring systems. 

Hydrogenative ring opening of cycloalkanes is also a well-studied area.16 252 253 289-292 Mainly cyclopropanes and cyclopentanes were studied, since three- and five-membered adsorbed carbocyclic species are believed to be intermediates in metal-catalyzed isomerization of alkanes (see Section 4.3.1). Ring-opening reactivity of different ring systems decreases in the order cyclopropane > cyclobutane > cyclopentane > cyclohexane.251 Cyclopropane and its substituted derivatives usually react below 100°C. 

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