Cyclopentene cross-metathesis

Conversions of about 80% were obtained within a few minutes at 90°C. The polymer could also be cleaved by cross-metathesis with an excess of 4-octene which gave, as the main product, 9-tridecenyl-7-undecenoate, thus confirming the structure assignment as indicated in Eq. (62). The unsaturated lactone was also copolymerized with cyclooctene, 1,5-cy-clooctadiene, and cyclopentene under the previously stated conditions to afford linear copolymers which were high molecular weight, unsaturated, rubbery polyesters (110). 

Cross-metathesis of terminal alkyne 142 and cyclopentene gives cyclic compound 143 having a diene moiety [Eq. (6.114)]. ° Terminal ruthenium carbene generated from an alkyne and methylidene ruthenium carbene complex reacts with cyclopentene to afford two-carbon elongated cycloheptadiene 143 ... 

Ruthenium catalysts, coordinated with an N-heterocyclic carbene allowed for the ROMP of low-strain cyclopentene and substituted cyclopentenes (10,23). Suitable ruthenium and osmium carbene compounds may be synthesized using diazo compounds, by neutral electron donor ligand exchange, by cross metathesis, using acetylene, cumulated olefins, and in an one-pot method using diazo compounds and neutral electron donors (24). The route via diazo compounds is shown in Figure 1.7. 

A pairwise mechanism involving a quasi-cyclobutane structure was suggested first, Eq. (3) [18], but cross metathesis between cyclopentene and 2-pentene produced a statistical ratio of cross-products 1-3 (1 2 3 = 1 2 1), Eq. (4) [19]... 

The intermolecular enyne cross metathesis, and consecutive RCM, between a terminal alkyne and 1,5-hexadiene produces cyclohexadienes, by cascade CM-RCM reaction, and trienes, formed during the sole CM step. Studies of various parameters of the reaction conditions did not show any improvement of the ratio of desired cyclohexadiene product [25] (Scheme 12). The reaction with cyclopentene instead of hexadiene as the alkene leads to 2-substituted-l,3-cycloheptadienes [26]. After the first cyclopentene ROM, the enyne metathesis is favored rather than ROMP by an appropriate balance between cycloalkene ring strain and reactivity of the alkyne. 

The cross-metathesis of cyclopentene with imsymmetrical olefins is catalyzed by WOCl4/Bu4Sn or WOCl4/Et2AlCl. Herisson (1971) observed that the products of reaction with pent-2-ene consisted of three series of compounds Q M Q , Q M Q, and Q M Q (n = 1-4), where Q = ethylidene, = propylidene, and M represents n ring-opened units of cyclopentene M. These series were formed in the statistical ratio 1 2 1 even in the initial products. Similar results were obtained with cyclooctene, cycloocta-1,5-diene, and cyclododeca-l,5,9-triene in place of cyclopentene. It was these observations that led to the proposal of the metal carbene mechanism, since direct exchange between the double bonds of the reactant molecules would yield only the unsymmetrical series. The formation of the three series of compounds is accounted for in terms of reactions (l)-(6). 

Fig. 15.2 GC of the polyenes obtained by cross-metathesis of cyclopentene (CPE) and pent-l-ene (C5). Catalyst system WCl6/EtAlCl2/CCl3CH20H in benzene at 25°C. Internal...

The synthesis of a,co-difunctional telomers by cross-metathesis between cyclic olefins and acyclic functionalized olefins is possible in the presence of functional-group-tolerant catalysts. Thus, cross-metathesis of dimethyl hex-3-enedioate with cycloocta-1,5-diene (Pinazzi 1980 Reyx 1982b, 1990), cyclopentene (Reyx 1986, 1987), or norbomene (Cramail 1991a) in the presence of the catalyst system WCV Mc4Sn allows the synthesis of a,m-difunctional oligomers, e.g. reaction (2). 

We have seen that end-groups may be detected by C NMR spectra and inferred from mass spectra. Other methods for the detection of end-groups in the products of cross-metathesis of cyclic and acyclic olefins include IR and UV spectra, and elementary analysis. For example, polymers of norbomene made in the presence of pent-l-ene show a band at 1375 cm attributable to methyl groups, and bands at 905 and 990 cm due to vinyl groups (Porri 1974). Such bands become stronger relative to the main band as [M2]/[Mi] is increased, thereby reducing the MW. Polymers of cyclopentene made in the presence of 5-(j3-naphthoxypent-l-ene) have... 

Scheme IS.2 Mechanism of cross-metathesis between cyclopentene and pent-l-ene P = polymer chain.

Chauvin and Herisson found in 1970, that the initial product distribution in the cross metathesis of cyclopentene and 2-pentene is not in accordance with such a simple pairwise mechanism [30,50]. Therefore, they proposed a novel non-pairwise mechanism with metal carbene complexes as intermediates (5) [50]. 

Water-soluble mthenium vinyUdene and aUenylidene complexes were also synthetized in the reaction of [ RuCl2(TPPMS)2 2] and phenylacetylene or diphenylpropargyl alcohol [29]. The mononuclear Ru-vinylidene complex [RuCl2 C=C(H)Ph)(TPPMS)2] and the dinuclear Ru-aUylidene derivative [ RuCl(p,-Cl)(C=C=CPh2)(TPPMS)2 2] both catalyzed the cross-olefin metathesis of cyclopentene with methyl acrylate to give polyunsaturated esters under mild conditions (Scheme 7.10). 

Polymers of monocyclic olefins (cyclopentene, cyclooctene) produced by ring-opening metathesis are linear elastomers. Their properties are somewhat similar to those of poly eri-1,4-hn i.idiene). Polymers of dicy-clopentadiene produced with the same catalysts are heavily cross-linked resins displaying high toughness and tensile strength as well as excellent impact strength at low temperatures. 

However, under certain conditions the double bond in the disubstituted cyclopentene ring may also undergo metathesis, thereby giving rise to cross-linking (eq. (21)). 

Ring-opening metathesis polymerization of dicyclopentadiene (DCPD) can take place by two different pathways in the first, the reaction occurs with opening of the norbornene unit leading to linear polydicyclopentadiene while in the second both the norbornene and cyclopentene rings are successively opened forming a cross-linked polymer (Scheme 1) [1-3]. Due to substantial differences in reactivity of the double... 

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