Alkenes olefin isomerization

Olefin isomerization can be catalyzed by a number of catalysts such as molybdenum hexacarbonyl [13939-06-5] Mo(CO)g. This compound has also been found to catalyze the photopolymerization of vinyl monomers, the cyclization of olefins, the epoxidation of alkenes and peroxo species, the conversion of isocyanates to carbodiimides, etc. Rhodium carbonylhydrotris(triphenylphosphine) [17185-29-4] RhH(CO)(P(CgH )2)3, is a multifunctional catalyst which accelerates the isomerization and hydroformylation of alkenes. 

A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

Fragments derived from photolysis of Fe(CO)s have been observed to catalyze olefin isomerization and hydrogenation (65-67). The key active species for the isomerization is iron tricarbonyl which can easily add alkene to give Fe(CO)3(alkene). 

Of the technological modifications, Fischer-Tropsch synthesis in the liquid phase (slurry process) may be used to produce either gasoline or light alkenes under appropriate conditions249,251 in a very efficient and economical way.267 The slurry reactor conditions appear to establish appropriate redox (reduction-oxidation) conditions throughout the catalyst sample. The favorable surface composition of the catalyst (oxide and carbide phases) suppresses secondary transformations (alkene hydrogenation, isomerization), thus ensuring selective a-olefin formation.268... 

Olefin isomerization has also been mediated by the photolysis of Fe(C0)s.144 Recently, a detailed study of alkene isomerization by photolysis of Fe(CO)5 has shown that the reaction is truly photocatalytic.14S The very high quantum yields ( 1.0), Table 24, and the fact that the pentenes are ultimately equilibrated to the thermodynamic ratio support the notion that the role of the light is to generate a thermally active catalyst. A mechanism similar to that in reactions (53)-(57) involving Fe(CO)3 as the repeating unit can be used to account for the results. 

A tandem RCM-alkene isomerization sequence to form 5-, 6-, and 7-membered enol ethers was reported by Snapper and co-workers <02JA13390> (Scheme 36). In this process the RCM reaction is run under an atmosphere of 95 5 N2.TI2 to convert the intermediate ruthenium alkylidene into an olefin-isomerization catalyst. Note that alkene migration can convert isomeric metathesis products into the same 2,3-enol ether. A single example of the formation of a 6-membered tosyl enamide was reported in this manuscript. 

Alkene positional isomerism is a problem that arises from time to time. It is conceptually related to regiochemistry and is presented here. Careful synthetic planning is usually required to solve this problem, as illustrated by the Burk-Soffer synthesis of e-cadinene (53) and V2-cadinene (54). 9 Conversion of 52 first to the ketone, then to the tertiary alcohol, and finally to the tertiary chloride allows E2 elimination to give 53. Conversely, Wittig olefination (sec. 8.8.A) of the ketone gave the exo methylene derivative, 54. It is important to note that formation of the C2-C3 C=C unit is favored for trans decalin derivatives over the C3-C4 unit. 

The MBH adduct shown in Scheme 3.162, prepared from aromatic aldehydes and methyl acrylate, can directly undergo smooth dehydroxylation with concomitant olefin isomerization with low-valent titanium (LVT, prepared from TiCls-LAH-THF) reagent to afford the trisubstituted alkenes 364 with high ( )-selectivity. However, it is unsatisfactory in view of the low yield and the purity of products.More recently, Zhang et al. developed the samarium diiodide-promoted hydroxyl elimination of MBH adducts to form trisubstituted alkenes 364 with total ( )-stereoselectivity in good to excellent yields. This method also provided a new route to synthesizing a class of 1,5-hexadiene derivatives 365 by temperature tuning (Scheme 3.162). ... 

Trialkylphosphine-modified cobalt catalysts and unmodified rhodium catalysts show similar olefin isomerization activity, but the most common tertiary phosphine-modified rhodium catalysts are generally ineffective in double-bond isomerization (77-79). On the other hand, phosphite-modified rhodium catalysts were found to be highly effective at alkene isomerization (80-83). 

Alkene isomerization/migration is an undesired side reaction in olefin metathesis. This isomerization has been attributed to ruthenium hydride species formed upon catalyst decomposition [63, 64]. Several computational investigations of ruthenium hydride-catalyzed olefin isomerization have been reported, in which the isomerization was found to occur via olefin insertion into the ruthenium hydride, rotation about the Ru-C a bond, and P-hydride elimination (Scheme 7.15a) [65, 66]. These processes typically require only relatively low activation barriers. Once the ruthenium hydride is formed, olefin isomerization... 

In 2012, the scope of substrates was extended to a series of functionalized alkenes [20]. Allyl alcohol produced only 31% of the desired alcohol, but a significant reduction of the olefin was complained about. The formation of y-isobutyrolactone was also observed. In contrast, longer alkenyl alcohols produced up to 95% (e.g., 1,6-hexanediol) of the desired diols. Protection of the alcoholic group (THP, Ac, Bn) had only a sUght effect. The contribution of the individual metal complexes to the single steps (olefin isomerization, hydroformylation, and hydrogenation) was clarified in a kinetic study. 

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