Ethyl oleate metathesis

The surface species is an active catalyst for propene metathesis (780 eq., TOI min = 0-89 molpropene hioImo s" for the catalyst obtained by the benzene impregnation route) and ethyl oleate metathesis (lOOeq. TOI mm =0.11 moloieate hioImo s for the catalyst obtained by the benzene impregnation route) [136]. The high catalytic activity of the surface neopentylidene complex has not been modeled by the silsesquioxane analogue [136]. 

Table 14.2 Comparison between silica-supported, silsesquioxane, and molecular Mo(VI) precursor as catalysts for octene and ethyl oleate self-metathesis.

The complex WOCI4—Cp2TiMe2 was used for the metathesis of ethyl oleate (51) to give diethyl 9-octadecenedioate (52). Civetone (53) was synthesized by the Dieckmann condensation of this diester, followed by decarboxylation [20], Homometathesis of terminal alkenes is useful, because it yields symmetric internal alkenes and ethylene, which can be removed easily. Metathesis of 10-undecenoate (54) proceeds smoothly to give the diester 55 [20],... 

Cross-metathesis reactions are useful for the production of fine chemicals such as synthetic perfumes, prostaglandin intermediates, and insect pheromones. An example of the last is the cross-metathesis of ethyl oleate with 5-decene in the presence of a MoCl5/Si02/Me4Sn catalyst at 90 °C [14], or a Mo03/Si02/cyclopropane catalyst at 50 °C [16], resulting in a cisitrans mixture of ethyl 9-tetradecenoate, an insect pheromone precursor (Eq. 12). 

Olefin metathesis has been exploited in a synthesis of civetone (46) from ethyl oleate (Scheme 15) and of the macrolide (47) from oleyl oleate (Scheme 16). ... 

Because the free enthalpy change in this type of reaction is virtually zero, the result at equilibrium is a random distribution of the alkylidene groups. Thus, starting with methyl oleate, the equilibrium mixture consists of 50 mol% of the starting material and 25 mol% of each of the products 9-octadecene and dimethyl 9-octadecene-1,18-dioate. The cis/trans ratio of the reaction products is also in accordance with thermodynamics. This demonstrates that - in the presence of a suitable catalyst - the metathesis of unsaturated fatty acid esters provides a convenient and highly selective route to unsaturated diesters. Unsaturated diesters are important intermediates for the production of useful chemical products such as macrocyclic compounds. For instance, the diester obtained by metathesis of ethyl oleate has been subjected to a two-step reaction sequence, i.e. a... 

Another example of organic synthesis via cross-metathesis is the synthesis of biologically active compounds such as insect pheromones. Use of such pheromones offers an effective and selective pest control method. Thus, cross-metathesis of ethyl oleate with 5-decene results in a cis-trans mixture of ethyl 9-tetradecenoate, an insect pheromone precursor [15]. Cross-metathesis of methyl d.y-5-eicosenoate (obtained from meadowfoam oil) with excess 5-decene gives methyl tm 5-decenoate, which can be transformed into a 83 17 mixture of trani -5-decenylacetate and tran.y-5-decenol (in total 90% trans), the sex pheromone of the Peach Twig Borer moth, a major pest in Northern Hemisphere fruit orchards. The isomeric mixture was active in mating disruption [16]. Other examples of organic synthesis via cross-metathesis are summarised elsewhere [17 18]. 

ABSTRACT. Cyclometalated aryloxy(chloro)neopentylidene-tungsten complexes can be synthesized starting from WCl4(OAr)2 (OAr = 2,6-disubstituted phenoxide), but also starting from the neopentylidyne complex W(CCMe3)Cl3(dme) (by reaction with LiOAr). Some of these cyclometalated neopentylidenes are probably among the most active and stereoselective one-component metathesis catalysts. In particular, they are fairly active in the metathesis of an olefinic ester such as ethyl oleate and they have been successfully used in the metathesis of olefinic sulfides. 

Application of cyclometalated neopentylidene complexes to the metathesis of olefinic esters. Very promising results were obtained in the metathesis of an olefin bearing an ester group such as ethyl oleate (ethyl-9-octadecenoate) (Scheme 5)... 

For example, 1 can convert selectively, in 60 min at 25 C, ca. 50% of 500 equiv of ethyl oleate into 9-octadecene and diethyl-9-octadecenedioate (with an initial turnover rate for the conversion of ethyl oleate higher than 800 h" ) (Figure 3). To our knowledge, this is the highest activity reported so far with homogeneous catalysts in the metathesis of Ais type of substrate [4, 9]. 

Figure 3. Yield of 9-octadecene vs. reaction time in the metathesis of ethyl oleate with 1 (ethyl oleate/1 molar ratio = 500, T = 25 C, solvent chlorobenzene (5 mL)).

The turnover rates (Table 3) are lower than those obtained with 1 in the metathesis of 2-pentene or ethyl oleate, suggesting a reversible coordination of the sulfur compound to the metallocarbene leading to a partial deactivation of the catalyst. Nevertheless, the reaction is highly selective (only the expected metathesis products are detected) and the conversion of 4 can reach a high value when an excess of the co-reactant olefin is used. 

Initial reports of cross-metathesis reactions using well-defined catalysts were limited to simple isolated examples the metathesis of ethyl or methyl oleate with dec-5-ene catalysed by tungsten alkylidenes [13,14] and the cross-metathesis of unsaturated ethers catalysed by a chromium carbene complex [15]. With the discovery of the well-defined molybdenum and ruthenium alkylidene catalysts 3 and 4,by Schrock [16] and Grubbs [17],respectively, the development of alkene metathesis as a tool for organic synthesis began in earnest. 

In situ product separation by distillation offers applications in esterification (e.g., for ethyl acetate), trans-esterification (e.g., for butyl acetate), hydrolysis (e.g., for ethylene glycol, isopropyl alcohol), metathesis (e.g., for methyl oleate), etherification (e.g., for MTBE, ETBE, TAME), and alkylation reactions (e.g., for cumene). 

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