Hexenes, cross-metathesis

Cross Metathesis of Nitrile Rubber with 1-Hexene... 

Cross-metathesis of methyl oleate with 3-hexene under similar conditions led, in addition to the above products [Eq. (54)], to 3-dodecene and the methyl ester of 9-dodecenoic acid. 

WC16 Na[Re04] [C4C im][BF4] [C4C1im]Cl-AlCl3 Cross-metathesis of linear olefins, e.g. conversion of 1-hexene to 4-octene and 5-decene rather low conversions (<15-30%) addition of 10-30% SnBu4 significantly increases the yield and the selectivity for 4-octene (> 95%). [25]... 

Cross-metathesis of oleyl acetate and 3-hexene produces, with 3-dodecene and self-metathesis products of the acetate, 9-dodecenyl acetate, the pheromone of a leaf roller, Eucosma sonomana. Even the isomeric mixture obtained from this metathesis reaction was active in disrupting insect mating [23]. Although many other pheromones have been synthesized by use of homogeneous catalysts these reactions might also be performed with suitable heterogeneous catalysts. 

The selectivity of cross-metathesis reactions has been demonstrated by the reaction of trans-3-hexene with vinyl acetate or a,yff-unsaturated esters (e. g. methyl rran -crotonate) in the presence of a supported rhenium oxide catalyst (Eq. 14). 

Apart from Ru-catalyzed metathesis in ionic liquids two examples of tungsten catalyzed metathesis reactions have also been reported. Vasnev and coworkers studied the metathesis of Thexene catalyzed by WCle in tetrafluoroborate ionic liquids [266]. In the reaction sequence under investigation, l-hexene first isomerized to 2-hexene which then formed 4-octene and ethylene by cross-metathesis. The yields of the metathesis product were demonstrated to increase with increasing reaction temperature and with addition of a tin-containing promoter. 4-octene was obtained in selectivies up to 97% (at 25% l-hexene conversion) when tetrabutyl tin was applied as the promoter in this reaction. 

On the other hand, instead of shortening the carbon chain of unsaturated esters, it is also possible to lengthen it, as illustrated for the cross-metathesis between methyl 10-undecenoate and 3-hexene in equation (6). 

EXSY experiments were performed at -87 °C (186 K) to determine the rate of exchange between the cis and trans stereoisomers of metallacycles 26a-c and 27a-c (Table 8.2). These rate constants incorporate the rates of metallacycle cycloreversion, alkylidene rotation, and cycloaddition to interconvert the two species. Given that propene, 1-butene, and 1-hexene are all Type I olefins for cross-metathesis [42], it is not unexpected that these results correlate with each other. 

The required terminal olefins used as substrates for the hydroformylation, such as 1-pentene or 1-octene, are available in large scales and can be derived either from Sasol s Fischer-Tropsch process or from the shell higher olefins process (SHOP), respectively [43, 44]. Alternatively, trimerization or tetramerization of ethylene affords 1-hexene [45] or 1-octene [46]. Dimerization of butadiene in methanol in the presence of a Pd catalyst (telomerization) is another industrially used access for the manufacture of 1-octene [46]. 1-Octene can also be produced on a large scale from 1-heptene via hydroformylation, subsequent hydrogenation, and dehydration (Scheme 6.2) [44]. This three-step homologation route is also valuable for the production of those higher olefins that bear an odd number of C atoms. (X-Olefins can also be derived from internal olefins by cross-metathesis reaction with ethylene [47]. 

Another study of CH2 and CD2 exchange between 1-hexene and [l,l-D2]-l-pentene showed that this reaction was approximatively 10 times faster than productive metathesis in WCl —BuLi or WCl —. AlEtCl2 systems [35]. The structural selectivity of metathesis reactions can be summed up as follows Degenerate exchange of =CH2 groups between terminal olefin > cross metathesis between terminal and internal alkenes > metathesis of internal olefins > non-degenerate metathesis of terminal alkenes. 

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