Cyclopentane structure

Cyclopolymerisation leading to polymers with monocyclic units in the main chain proceeds in two steps the first step involves a 1,2-insertion of the coordinated a, ffl-diolefin via one olefinic bond, and the second step, which is a ringclosing reaction, involves an intramolecular insertion of the other olefinic bond undergoing coordination scheme (89) presents both steps for 1,5-hexadiene cyclopolymerisation leading to a cycloaliphatic polymer with poly(methylene-1,3-cyclopentane) structural units [30,450,497] ... 

How many mono-, di-, and trichloro derivatives are possible for cyclopentane (Structure given in Sec. 9.5.)... 

The close relationship between monoterpenes and insects is, of course, well known, and work has intensified on what attracts, say, bark beetles to appropriate trees. One of the most intriguing aspects is the potentiating effect ethanol has on the aggregation of certain species when in conjunction with the pheromone. This aspect has little to do with total synthesis, but the discovery of new pheromones and defense secretions certainly has. Many are described in this chapter, but one of the more unusual types is the new cyclopentane structure found by Eisner and Meinwald in pheromones of certain carrion beetles, the synthesis of which is described in the appropriate section (Section 6). °... 

The direct formation of cyclopentane structure from alkane(s) on a metal was demonstrated by Kazanskii and Plate (44). Aromatic rings are... 

Fig. 16. Poly(methylene-l,3-cyclopentane) structures of maximum order.

In polybutadiene, a substituted cyclopentane structural unit has been identified for polymerization carried out at low concentration. It was suggested that this unit is due to an intramolecular cyclization involving a penultimate 1,2-unit. 

There are many examples of preparing cyclopentane structures from enynes by gold-catalyzed carbocyclization reactions. Toste et al. have reported that Au(l)-phosphine complexes act as superior catalysts for isomerization of 1,5-enynes to bicyclo[3.1.0]hexenes [124]. For example, treatment of 1,5-enyne (86) with 1 mol% of PhsP-AuPFfi in dichloromethane at room temperature results in formation of cyclopropane-fused cyclopentene (87) in 99% yield (Scheme 18.30). 1,6-Enynes also undergo similar cycloisomerization to five-membered cyclic compounds under the influence of cationic gold(l) catalysts [125, 126], Hydroxylated enynes are versatile precursors for cyclopentenones by gold-catalyzed cycloisomerization... 

The cyclohexane structure is structural features drawn simply as a hexagon and the cyclopentane structure as a pentagon. In such drawings, it is understood that there is a carbon in every corner and that there are two hydrogens bonded to each carbon, even though neither the hydrogens nor the bonds are shown. Such a structure is sometimes referred to as a bond-line structure (Figure 14.19a). 

Cyclopentane is nonplanar, with a structure that resembles an envelope (see Fig. 1.5). Four of the carbon atoms are in one plane, and the fifth is out of that plane. The molecule is in continual motion so that the out-of-plane carbon moves rapidly around the ring. 

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. 

Fig. 7-6). Two unichiral amides which have been known capable of this reaction are 1-phenylethylamine [15] and l-(l-naphthyl)ethylamine [16]. Marfey s reagent [N-a-(2,4-dinitro-5-fluorophenyl)-L-alaninamide] was introduced as a reagent to deriva-tize amino acids with cyclopentane, tetrahydroisoquinoline or tetraline structures [17]. Simple chiral alcohols such as 2-octanol can also be used to derivatize acids such as 2-chloro-3-phenylmethoxypropionic acid [18]. 

Prostaglandin F, a hormone that causes uterine contraction during childbirth, has the following structure. Are the two hydroxyl groups (-OH) on the cyclopentane ring cis or trans to each other What about the two carbon chains attached to the ring ... 

Petroleum contains hydrocarbons other than the open-chain alkanes considered to this point. These include cycloalkanes in which 3 to 30 CH2 groups are bonded into closed rings. The structures of the two most common hydrocarbons of this type are shown in Figure 22.5 (p. 585). Cyclopentane and cyclohexane, where the bond angles are close to the ideal tetrahedral angle of 109.5°, are stable liquids with boiling points of 49°C and 81°C, respectively. 

The chain and branched chain saturated hydrocarbons make up a family called the alkanes. Some saturated hydrocarbons with five carbon atoms are shown in Figure 18-11. The first example, containing no branches, is called normal-pentane or, briefly, n-pentane. The second example has a single branch at the end of the chain. Such a structural type is commonly identified by the prefix iso- . Hence this isomer is called /50-pentane. The third example in Figure 18-11 also contains five carbon atoms but it contains the distinctive feature of a cyclic carbon structure. Such a compound is identified by the prefix cyclo in its name—in the case shown, cyclopentane. 

PGF2a- The cyclopentane ring of the Corey lactone (9) is the host of four contiguous stereogenic centers. Retrosynthetic simplification of 9 provides 10, a construct which is more complex than 9 Nevertheless, intermediate 10 possesses structural features that satisfy the requirement for the iodolactonization transform. The iodolactone in 10 constitutes the retron for the iodolactonization transform.11 Cleavage of the indicated bonds in 10 sacrifices two of the five stereocenters and provides unsaturated carboxylic acid... 

The reaction of methyl acrylate and acrylonitrile with pentacarbonyl[(iV,iV -di-methylamino)methylene] chromium generates trisubstituted cyclopentanes through a formal [2S+2S+1C] cycloaddition reaction, where two molecules of the olefin and one molecule of the carbene complex have been incorporated into the structure of the cyclopentane [17b] (Scheme 73). The mechanism of this reaction implies a double insertion of two molecules of the olefin into the carbene complex followed by a reductive elimination. 

Identify each of the following pairs as structural isomers, geometrical isomers, or not isomers (a) butane and cyclobutane (b) cyclopentane and pentene ... 

Fig. 8 Superimposition of inhibitors and key active site residues in influenza A virus sialidase cyclopentane-based inhibitor peramivir 34 (brown carbons, PDB - 117f), Neu5Ac2en 4 (green carbons, PDB - lf8b). Note the overlap of the carboxyl and acetamido-methyl groups of the inhibitors, and the alternative conformations of the side-chain of Glu276. To the right is shown peramivir 34 oriented as in the crystal structure...

Chan T-H, Xin Y-C, von Itzstein M (1997) Synthesis of phosphonic add analogs of siaUc acids (Neu5Ac and KDN) as potential sialidase inhibitors. J Org Chem 62 3500-3504 Chand P, Kotian PL, Dehghani A, El-Kattan Y, Lin T-H, Hutchison TL, Babu YS, Bantia S, Elliott AJ, Montgomery JA (2001) Systematic structure-based design and stereoselective synthesis of novel multisubstituted cyclopentane derivatives with potent antiinfluenza activity. J Med Chem 44 4379 392... 

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