1,7-Octadiene, metathesis

Deeatriene may, of course, react further to 1,5,9,13-tetradeca-tetraene, 1,5,9,13,17-octadecapentaene, etc. (18). Even the conjugated system 1,3-butadiene participates in metathesis reactions (14). An example of an intramolecular process is the reaction of 1,7-octadiene, which gives cyclohexene and ethene (13, 15) ... 

The purpose in offering this rather complicated scheme was to rationalize the presence of minor amounts of 1-butene in the metathesis of 1,7-octadiene, thus requiring existence of a propylidene moiety. 

V.P. Conticello, D.L. Gin, and R.H. Grubbs, Ring-opening metathesis polymerization of substituted bicyclo[2.2.2]octadienes a new precursor route to poly(p-phenylene vinylene), J. Am. Chem. Soc., 114 9708-9710, 1992. 

Damez C, Bouquillon S, Henin F, Muzart J (2006) Reactivity of l-phenoxy-2,7-octadiene under metathesis conditions. Eur J Org Chem 2006 4565 1567... 

Dimerization of butadiene is used for the selective formation of 1,5-cyclo-octadiene (1,5-COD), which on selective hydrogenation gives cyclooctene. By ring-opened metathesis polymerization of cyclooctene a specialty polymer is obtained (see Section 7.6.1). Hulls sells this polymer as Vestenamer . 

The polymerization of ether and thioether monomers was also studied, and it was found that the rate of polymerization was a great deal slower with the functionalized monomers. The number of methylene units between the olefin and the heteroatom greatly affected the rates observed, giving credence to the chelation effect shown in Fig. 6.1. In addition, catalyst 2 polymerizes 1,5-hexadiene, whereas catalyst 6 mainly cyclizes the metathesis dimer to cyclo-l,5-octadiene. At this point there is no clear explanation for this result, and, furthermore, the reason that the COD generated did not undergo ROMP in these reactions is unclear. The data from these experiments clearly shows that Lewis basic functionality retards the rate of metathesis with complex 6 more than with complex 2, although 6 is clearly the more functional group-tolerant complex overall [35]. 

Further mechanistic studies ruled out the original pairwise [2 + 2] mechanism and provided additional support for the Chauvin mechanism. Labeling studies, such as the experiment in Fig. 4.18, revealed that the kinetic product (the product at low conversion) of the metathesis of 1,7-octadiene derivatives is a statistical distribution (1 2 1) of d -, d2-, and ii 44abeled ethylene [58]. This is inconsistent with the pairwise [2 + 2] mechanism, which would have produced a non-statistical distribution (1 1.6 1) of labeled ethylene. 

During ring-opening metathesis polymerization (ROMP) of norbornadiene (NBD) with the Grubbs catalyst a free radical is also observed as a 1 2 1 triplet, which is also formed, but to a much weaker extent, with norbornene (NBE), cyclopentene and 1,7-octadiene. The identity of this triplet, and that of a transient doublet observed together with the triplet in the case of benzonorbornadiene, are discussed as well as the possible role of radicals in initiation of ROMP, crosslinking of ROMP products, and polymerization of a-methylstyrene. 

In order to explain reactions of olefins with carbene complexes, the fomation of metallacyclobutane compounds has been postulated [equations (5.127)-(5.131)]. The validity of the carbene mechanism is supported by metathesis reactions of 1,7-octadiene... 

Cross-Enyne Metathesis/Diels-Alder MCRs Ruthenium-based complexes are known to catalyze the metathesis between alkynes and alkenes to afford 1,3-dienes. Fnstero, del Pozo et al. further exploited this cross-enyne metathesis (CEYM) by trapping the 1,3-diene with a dieno-phile via an intermolecnlar Diels-Alder reaction [198]. Thns, the Ru-catalyzed MCR between alkynes 220-221 and 1,7-octadiene as an in situ sonrce of ethylene by RCM generates a 1,3-diene that can snbseqnently nndergo a Diels-Alder reaction with a wide variety of dienophiles 222... 

S. Fustero, P. Bello, J. Mird, A. Sim6n, C. del Pozo, Chem.-Eur. J. 2012, 18, 10991-10997. 1,7-Octadiene-assisted tandem multicomponent cross-enyne metathesis (CEYM)-Diels-Alder reactions a useful alternative to Mori s condition. 

Hexadiene motifi have been found to lead to sequestration of the catalyst in some reactions. Snapper isolated T -complex 86 from the ringopening reaction of cyclobutene 87 with G1 as well as from the metathesis of 1,5-hexadiene 88 (Scheme 2.35). The stability of this product was such that it could be isolated and crystaUized, so this represents an extreme case. In a later study, Percy and coworkers showed that even the simplest parent molecule, 1,5-hexadiene, reduced the rate of RCM reactions of 1,6-heptadiene and 1,7-octadiene, suggesting that the formation of such T -complexes impedes RCM reactions via catalyst sequestration. 

Under standard conditions all unsubstituted cycloolefins apart from cyclohexene are metathetically polymerizable (Table 4). In fact, polymers of (Z, )-cyclodeca-1,5-diene [251] or 1,3-cyclooctadiene [252] containing 1,7-octadiene units pinch off cyclohexene in the presence of suitable metathesis catalysts. But even cyclohexane has recently been oligomerized at lower temperature [253]. 

The cross-metathesis of 1,9-octadiene with an excess of trialkoxy- and trisiloxy-substituted vinylsilanes results in the formation of bis(silyl)dienes (Eqs. 7 and 8) [14]. 

Reaction mechanism As discussed in Sect. 2.3.1, [ (ArNCMe)2CH Ca(p-H) (THF)]2 undergoes insertion reactions with 1,1-diphenylacetylene and myrcene (7-methyl-3-methylene-l,6-octadiene), a terpene that contains three double bonds [121]. Experimental evidence for the o-bond metathesis step was provided by not only the reaction of the calcium complexes isolated from these latter reactions with H2 but also an H/D exchange reaction. Treatment of the calcium deuteride [ (ArNCMe)2CH Ca(p-D)(THF)]2 with 1 bar H2 at 20 °C led to complete H/D exchange after 20 min at room temperature as evidenced by NMR spectroscopy. The reaction of H2 with Ca-C bonds required slightly more forcing reactions conditions and, consistent with those reported for the catalytic reaction, could be achieved at 20 bar H2 at 20 °C in either benzene or THF solution [130]. 

Apart from halogen substituted alkenes, heteroatoms normally deactivate catalytic systems. However the synthetic utility of such reactions has encouraged further research in this field. Chlorine substitution at vinylic positions deactivates the double bond but halogen substituted alkenes in which the double bond is in an position undergo cross metathesis with internal alkenes. For example, 5-bromo-l-pentene undergoes cross metathesis with 2-pentene. Unsaturated compounds containing ester groups also react, e.g. methyl-9-octadecenoate is converted to 9-octadiene and dimethyl-9-octadecenedioate by the WCl —Sn(CH3)4 catalytic combination [15]. 

The metathesis reaction offers some opportunities for the synthesis of highly pure cycloolefins, as well. A first efficient method consists of the metathesis cycli-zation of linear a, co-dienes in the presence of tungsten- or molybdenum-based catalysts. Ethene or other low alkenes formed as by-products are easily removed from the reaction mixture, enabling convenient separation of the cycloalkene. A pertinent example is the synthesis of cyclohexene, in high yield, from 1,7-octadiene with molybdenum nitrosyl complexes [23] ... 

I advise Dr. Maxwell to make a polymer of methyl substituted cyclo-octadiene, which can be done via an ordinary metathesis process using butyl lithium and tungsten hexachloride. A ring system can be made. I d like to see how this polymer behaves in Maxwell s experimental system. Would one get rid of one of the T>Tg peaks ... 

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