Cross-metathesis butenes

Olefin metathesis of vinylboronates [102] and allylboronates [103, 104] has been investigated over the past few years because organoboranes are versatile intermediates for organic synthesis. Cross metathesis of vinylboronate 108 and 2-butene 109, for example, yields the boronate 110, which can be converted to the corresponding vinyl bromide 111 with high Z selectivity. Vinyl iodides can be obtained analogously. It should be noted that vinyl bromides and vinyl... 

The final stereochemistry of a metathesis reaction is controlled by the thermodynamics, as the reaction will continue as long as the catalyst is active and eventually equilibrium will be reached. For 1,2-substituted alkenes this means that there is a preference for the trans isomer the thermodynamic equilibrium at room temperature for cis and trans 2-butene leads to a ratio 1 3. For an RCM reaction in which small rings are made, clearly the result will be a cis product, but for cross metathesis, RCM for large rings, ROMP and ADMET both cis and trans double bonds can be made. The stereochemistry of the initially formed product is determined by the permanent ligands on the metal catalyst and the interactions between the substituents at the three carbon atoms in the metallacyclic intermediate. Cis reactants tend to produce more cis products and trans reactants tend to give relatively more trans products this is especially pronounced when one bulky substituent is present as in cis and trans 4-methyl-2-pentene [35], Since the transition states will resemble the metallacyclobutane intermediates we can use the interactions in the latter to explain these results. 

Above we have mentioned several heterogeneous applications such as the OCT process and SHOP. Neohexene (3,3-dimethyl-1-butene), an important intermediate in the synthesis of fine chemicals, is produced from the dimer of isobutene, which consists of a mixture of 2,4,4-trimethyl-2-pentene and 2,4,4-trimethyl- 1-pentene. Cross-metathesis of the former with ethene yields the desired product. The catalyst is a mixture of W03/Si02 for metathesis and MgO for isomerisation at 370 °C and 30 bar. The isobutene is recycled to the isobutene dimerisation unit [48],... 

Note also that, in contrast to classical heterogeneous catalysts, the initiation step of [=SiORe(=CtBu)(=CHtBu)(CH2tBu)] is well defined and corresponds to the cross-metathesis of the alkene with the neopentyhdene ligand. In fact, in the metathesis of propene, 0.7 equiv of a 3 1 mixture of 3,3-dimethyl-l-butene and 4,4-dimethyl-2-pentene is formed (Figure 3.27) the nearly quantitative formation of cross-metathesis products is consistent with a real single-site catalyst. Moreover,... 

As discussed in Section 12.3, the triolefin process to transform propylene to ethylene and 2-butene developed by Phillips135,136 is not practiced at present because of the increased demand for propylene. The reverse process, that is, cross-metathesis of ethylene and 2-butene, however, can contribute to satisfy the global demand for propylene. Lyondell Petrochemical operates a 136,000-t/y (ton/year) plant for the production of propylene.236 In a joint project by BASF and FINA, Phillips metathesis technology will be used to enhance propylene production.237 A similar project was also announced by DEA.238 In a continuous process jointly developed by IFP and Chines Petroleum Corporation, cross-metathesis of ethylene and 2-butene is carried out in the liquid phase over Re207-on-Al203 catalyst (35°C, 60 bar).239,240... 

Resin-bound (4-acyloxy-2-buten-l-yl)silanes, which can be prepared from resin-bound allylsilanes and allyl esters by cross-metathesis, react with dilute TFA to yield free carboxylic acids (Figure 3.7 [75]). However, the scope of this strategy remains to be explored. Similarly, esters of polystyrene-bound (2-hydroxyethyl)silanes readily undergo acidolysis and have been used as acid-labile linkers (Figure 3.7 [76]). 

Scheme 7 Cross metathesis with symmetric olefins, (a) methyl oleate with m-2-butene-1,4-d iyl diacetate [67], and (b) 10-undecenoate with diethyl maleate [68]...

Self Cross-Metathesis of Labeled and Unlabeled 2-Butene... 

Dimersol E is used to upgrade C2 + C3 fuel gas. Co-oligomerization of ethylene and propene leads to a gasoline stream very similar to the Dimersol G product. Mixed butenes are also obtained with Dimersol E (from ethylene dimerization). They can be used in paraffinic alkylation or to make propene through a subsequent cross-metathesis reaction with ethylene. 

Metathesis is a versatile reaction that forms the basis for several important industrial processes, such as the Phillips triolefin process, which produces propene by cross-metathesis of 2-butene with ethene, and the Shell higher olefins process (SHOP), which involves a combination process that converts ethene to detergent-range olefins. Several interesting polymeric materials are commercially produced via the ROMP of different types of unsaturated cyclic monomers, including nor-bornene, cyclooctene, and dicyclopentadiene [1]. 

Cross-metathesis. Functionalization of terminal alkenes by the metathetic method using catalyst 1 has been well established. The reaction between styrene and vinylsilanes gives (o-silylstyrenes, between allylarenes and acrylonitrile leads to 4-aryl-2-butenonitriles. Alternatively, homo-metathesis of two allylarene molecules to give 1,4-diary 1-2-butene is first carried out and the cross-metathesis follows. Also of interest is the homo-metathesis of monosubstituted allenes to symmetrical allenes. ... 

One of the classical experiments in the development of olefin metathesis was the double cross metathesis in which a mixture of cyclooctene, 2-butene, and 4-octene underwent metathesis. 

When cross-metathesis was first discovered, propene enjoyed only limited use and the reaction was viewed as a potential source of ethylene. Once methods were developed for the preparation of stereoregular polypropylene, however, propene became more valuable and cross-metathesis of ethylene and 2-butene now serves as a source of propene. 

More examples of efficient metathetical activity were found in cross-metathesis of allyl-and butenylsilanes, e.g. for the synthesis of l,4-bis(triorganosilyl)-butene-2 [3-5] and in the cross-metathesis of alkenylsilanes with polyalkenes [6]. 

In a subsequent report, the CAAC-based metathesis catalysts were examined for selectivity in the formation of Z E olefins, as well as their activity for ethenolysis [12]. Both of these processes require kinetic selectivity to produce the thermodynamically less-favored Z and terminal olefins, respectively. It was discovered that the CAAC catalysts displayed improved conversion to the Z olefin EIZ= 1.5—2.5 after 70% conversion) for the cross metathesis of cis-l,4-diacetoxy-2-butene with allylbenzene, relative to that observed using the classical NHC- and phosphine-based systems ElZ = 3-4) at comparable conversion (Scheme 4.3). 

Scheme 4.3 Cross metathesis of c s-1,4-diacetoxy-2-butene with allylbenzene.

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. 

Taber, D. F. and Frankowski, K. J. Grubbs Cross Metathesis of Eugenol with cis-l,4-butene-l, 4-diol to Make a Natural Product, Journal of Chemical Education, 2006, 83, 283-284. Experiment developed by Conrardy, D. and Lampman, G. M., Western Washington University, Bellingham, WA. 

The only oxide that has been used for catalyzed olefin metathesis at 25°C is Re207/Al203 (in the middle of the 1960s by British Petroleum), but it suffered from a low number of active sites, side reactions caused by the acid support and deactivation of the catalyst. On die other hand, the silica-supported rhenium catalyst [(SiO)(Re(C-f-Bu)(=CH-f-Bu)(CH2-f-Bu)] catalyzes the metathesis of propene at 25°C with an initial rate of 0.25 mol/(mol Re x s). The formation of 3,3-dimethyl-butene and 4,4-dimethylpentene in a 3 1 ratio results from cross metathesis between propene and the neopentyl idene ligand, and die ratio of cross-metathesis products matches the relative stability of the metallacyclobutane intermediates. Cross metathesis of propene and isobutene and self-metathesis of methyl oleate can also... 

The kinetic selectivity of the CAAC-based catalysts was investigated by probing the EjZdiastereoselectivity in the cross-metathesis of cA-l,4-diaceto-2-butene with allylbenzene (Equation (5.4)). Compared to the commercially available Grubbs catalysts, 66-68 afforded lower EjZ ratios (3 1 at 70%... 

Mixed WOj/Al Oj/HY catalysts prepared by calcination of physically mixed WO3, Al Oj and HY zeolite showed unique behavior in the metathesis between ethene and 2-butene to produce propene [147]. Monomeric tetrahedrally coordinated surface tungstate species responsible for the metathesis activity were formed via the interaction with Bronsted acid sites of HY zeolite. Polytungstate clusters are supposed to be less active in the metathesis reaction. The best catalyst demonstrates the 2-butene conversion close to the thermodynamic equilibrium value ( 64%) at 453 K. The catalysts are bifunctional [148] they catalyze first isomerization of 1-butene to 2-butene and then cross-metathesis between 1-butene and 2-butene to produce propene and 2-pentene. 10%W03/Al203-70%HY exhibits the highest propene yield. 

For the Mo/H-Beta zeolites, the formation of the Al2(Mo04)3 phase and the decrease in the concentration of Brpnsted acid sites explains the low catalytic activity of Mo/H-Beta in metathesis of ethylene and 2-butylene to propylene [149]. A promoting effect of Mg was revealed in the Mo/H-Beta-Al203 catalyst for cross-metathesis of ethene and butene-2 to propene [150]. The stability is improved at the Mg content of l-2wt.% due to the elimination of weak acid sites and suppression of the side olefin oligomerization reaction. 

In order to avoid side reactions, particularly isomerization, alkaline ions can be added during the impregnation stage of catalyst preparation. By this method, 1-butene production can be greatly reduced during metathesis of propylene and thus avoid the synthesis of other olefins by cross disproportionation between the normal metathesis products and the isomerized products. 

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