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Cyclopentane trans isomer

RhH(PPh3)4 (1 mol%) exhibited higher catalytic activity and promoted a complete reversal in stereoselectivity to provide the trans isomer of 24 and 25 as the major reaction product. The czs-cyclopentane 29, derived from optically active 28, was converted to the differentially protected cyclopentane triol 29, which, in turn, converted to the differentially protected tetrad 30, a key intermediate in the synthesis of enantiopure bioactive carbo-cyclic nucleosides [19]. [Pg.120]

In the ring closures of the 1,2-disubstituted 1,3-difunctional cyclohexane, cycloheptane, and cyclooctane derivatives discussed in Sections II,A,B, and C, no appreciable differences were found in the reactivities of the cis and trans isomers. In contrast, very significant differences were observed in the cyclization reactivities of the cis and trans 1,2-disubstituted 1,3-difunctional cyclopentane derivatives, such as 1,3-amino alcohols, 2-hydroxy-l-carboxamides or /S-amino acids. Whereas the cis isomers reacted readily, their trans counterparts did not undergo ring closure in most cases. This difference was manifested in the formation of both d - and e -fused derivatives. [Pg.398]

Figure 3-13 compares the cis-trans isomers of but-2-ene with those of 1,2-dimethyl-cyclopentane. Make models of these compounds to convince yourself that cis- and trans-1,2-dimethylcyclopcntanc cannot interconvert by simple rotations about the bonds. [Pg.109]

Most of the major metabolites of linolenic acid, listed in Figure 35, contain the cyclopentane (or -ene) ring and the two side chains arrayed in the cis fashion on the ring. Some of the metabolites, however, take the tram arrangement. Although isomerization to the trans isomer during isolation/purification is a likely process, a... [Pg.78]

The diester 110 (E = C02Et) reacts with a mixture of trimethyltin chloride and sodium cyanoborohydride under AIBN catalysis to give the cyclopentane 111 as a 4 1 mixture of cis- and trans-isomers. The products are destannylated to the acetals 112 by treatment with methanolic ceric ammonium nitrate (CAN). The 1,7-octadienyl derivative 113 was similarly converted into the cyclohexanes 114 (cis/trans =1 1) (equation 60). ... [Pg.523]

Another example is the preparation of l,2-di(methoxycarbonyl)-4-cyclopentanone. This compound has been prepared from dimethylmaleate as a mixture of its cis- and trans-isomers (yield 45-55 %) 235). A second approach starts with the Diels-Alder adduct of 1,3-butadiene and maleic anhydride and leads to the trans-diacid (yield 40 %)236). The oldest preparation of 1,2-di(methoxycarbonyl)-4-cyclopentanone stems from Auwers in 189 3 237). Now, the trans-isomer is available from methylenecyclopropane and dialkylfumerate in an overall yield of 85 %, whereas the pure m-isomer can be obtained from methylenecyclopropane and dialkylmaleate in 53 % yield. With dimethylmaleate, the Pd(0) catalyzed codimerization leads to a cis/trans-mixture of 4-methylene-l,2-cyclopentane-dimethylcarboxylate in the ratio 8 2 under optimal conditions (see Table 11) after oxidation, the pure c/ s-cyclopentanone derivative can be isolated by simple crystallization from pentane 193 195>. [Pg.140]

Lead tetraacetate is very frequently used for cleavage of 1,2-diols and preparation of fhe resulting carbonyl compounds. The rate of reaction is highly dependent on the stereochemistry of the substrate. There is usually correlation between the rate of oxidation and the spatial proximity of the hydroxy groups. For example, the rate of the oxidative cleavage of cis-cyclopentane-l,2-diol is much faster than that of trans isomer. It is, however, possible to oxidize trans-l,2-diol to diketone (Scheme 13.51) [72 a]. [Pg.741]

The ideal substrates for these reactions are 1,6-dienes [37-38], for example (Scheme 7), dimethyl diallylmalonate is easily transformed into cyclopentane derivatives, as a mixture of cis and trans isomers. The methodology also applies to analogous enynes [39-40], diynes [41], or eneallenes [42]. The radical acceptor in the cyclization step can even be an imino group [43a-c], or a nitrile [43d]. [Pg.990]

It is noteworthy that the ring closures of 1,2-disubstituted cyclohexane, cycloheptane and cyclooctane derivatives revealed no appreciable differences in the reactivities of the cis and trans isomers in the formation of six-membered 1,3-heterocycles [117]. In contrast, striking differences were observed in the cyclizations of the cis and trans cyclopentane derivatives. For instance, the above cyclizations to pyrimidinones, starting from the trans counterparts, were unsuccessful. The attempted ring closure from 104 did not result in the cyclized products, but gave hydrolysed derivatives 105 and 106 [111]. [Pg.292]

The most frequent cyclopentane conformations show carbon atoms that carry two substituents equally disposed above and below the ring plane (Fig. 1.2.7). These are called isoclinal (i). Substituted cyclopentanes usually do not show significant conformational preferences. cw-l,3-Dimethylcyclopentane, for example, is only 0.5 kcal/mol more stable than the trans isomer, compared with an approximate 2 kcal/mol difference between the 1,3-dimethyl-cyclohexanes. [Pg.11]

The ring of cyclopentane is almost flat and gives rise to cis- and trans- isomers, as though it were a big double bond. The ring of cyclohexane, although not flat, is flat enough to give this result. Thus both cis- 12.25) and trans- 12.26) forms of... [Pg.501]

Figure 6-1 I shows a cyclic case where one of the faces of a cyclopentane ring has been labeled by a deuterium atom. Deuterium has the same size and shape as hydrogen and it undergoes the same reactions. It distinguishes between the two faces of the ring The bromine atom is cis to the deuterium in the reactant, so the nucleophile is cis to the deuterium in the retention product. The nucleophile is trans to the deuterium in the inversion product. The product mixture contains both cis and trans isomers, with the trans isomer slightly favored because the leaving group hinders approach of the nucleophilic solvent from the front side. Figure 6-1 I shows a cyclic case where one of the faces of a cyclopentane ring has been labeled by a deuterium atom. Deuterium has the same size and shape as hydrogen and it undergoes the same reactions. It distinguishes between the two faces of the ring The bromine atom is cis to the deuterium in the reactant, so the nucleophile is cis to the deuterium in the retention product. The nucleophile is trans to the deuterium in the inversion product. The product mixture contains both cis and trans isomers, with the trans isomer slightly favored because the leaving group hinders approach of the nucleophilic solvent from the front side.
Using a planar pentagon representation for the cyclopentane ring, draw structural formulas for the cis and trans isomers of (See Examples 3.10, 3.11)... [Pg.101]

First, note that this compound exists in cis and Irans forms and that the latter is much more highly strained. (It may not be evident from the structures shown, but while the internal and external C-C-C bond angles at the bridgehead carbon are lOb-O and 115.4°, respectively, in the cis isomer, those in the Irans are 102.3° and 125.8°.) If we use two cyclopentane increments, we can calculate approximately correctly the heat of formation for the cis isomer, where the total strain is approximately the same as that of two cyclopentanes. But the trans isomer is much more strained than that (about 6kcal/mol more), due to very distorted bond angles, and the calculated heat of formation value would be very wrong. [Pg.260]

FIGURE 4. a) Influence of DIPIP/Li ratio on chemical shifts of the y carbon in isoprenyllithium in cyclopentane at 20°. Major peak-cis isomer, minor peak-trans isomer. [Pg.45]

In principle, three kinds of structural isomerism are possible, i.e., cis and trans isomers of the cyano group with respect to the two 1,3-bonds of the cyclopentane ring, cis and trans isomers about the C=C bond and the head-to-tail and head-to-head (tail-to-tail) arrangements of the consecutive monomer units. [Pg.312]

The alkaline hydrolysis of ethyl c/s-2-hydroxycyclopentanecarboxy-late is 1.8 to 11 times faster than that of ethyl cyclopen tanecarboxy late but this rate difference probably does not arise from intramolecular catalysis since the trans-isomer for which such catalysis is unlikely reacts even faster. The solvent dependence of the rates of both the cis- and lrans-2-hydroxy esters in aqueous dioxan is much smaller than that for ethyl cyclopentane-2-carboxylate and this was tentatively attributed to solvent sorting [53]. [Pg.354]


See other pages where Cyclopentane trans isomer is mentioned: [Pg.282]    [Pg.95]    [Pg.107]    [Pg.303]    [Pg.109]    [Pg.354]    [Pg.394]    [Pg.402]    [Pg.413]    [Pg.163]    [Pg.43]    [Pg.105]    [Pg.355]    [Pg.282]    [Pg.107]    [Pg.287]    [Pg.20]    [Pg.1175]    [Pg.92]    [Pg.160]    [Pg.237]    [Pg.243]    [Pg.237]    [Pg.243]    [Pg.185]    [Pg.84]    [Pg.367]    [Pg.80]    [Pg.524]    [Pg.176]   
See also in sourсe #XX -- [ Pg.12 ]




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Cyclopentane

Cyclopentanes

Trans isomers

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