Heptenes metathesis

It also explains the /Z selectivity of products at low conversions (kinetic ratio. Scheme 19). In the case of propene, a terminal olefin, E 2-butene is usually favoured (E/Z - 2.5 Scheme 19), while Z 3-heptene is transformed into 3-hexene and 4-octene with EjZ ratios of 0.75 and 0.6, respectively, which shows that in this case Z-olefins are favoured (Scheme 20). At full conversion, the thermodynamic equilibriums are reached to give the -olefins as the major isomers in both cases. For terminal olefins, the E olefin is the kinetic product because the favoured pathway involved intermediates in which the [ 1,2]-interactions are minimized, that is when both substituents (methyls) are least interacting. In the metathesis of Z-olefins, the metallacyclobutanes are trisubstituted, and Z-olefins are the kinetic products because they invoke reaction intermediates in which [1,2] and especially [1,3] interactions are minimized. 

Titanium-catalyzed cyclization/hydrosilylation of 6-hepten-2-one was proposed to occur via / -migratory insertion of the G=G bond into the titanium-carbon bond of the 77 -ketone olefin complex c/iatr-lj to form titanacycle cis-ll] (Scheme 16). cr-Bond metathesis of the Ti-O bond of cis- iij with the Si-H bond of the silane followed by G-H reductive elimination would release the silylated cyclopentanol and regenerate the Ti(0) catalyst. Under stoichiometric conditions, each of the steps that converts the enone to the titanacycle is reversible, leading to selective formation of the more stable m-fused metallacycle." For this reason, the diastereoselective cyclization of 6-hepten-2-one under catalytic conditions was proposed to occur via non-selective, reversible formation of 77 -ketotitanium olefin complexes chair-1) and boat-1), followed by preferential cyclization of chair-1) to form cis-11) (Scheme 16). 

Polymers using the ring opening metathesis polymerization (ROMP) technique were first obtained at 1960 by Eleuterio (1,2). The patents deal with the polymerization of bicyclo[2.2.1]heptene-2, i.e., nor-bomene using a molybdenum catalyst dispersed on alumina. 

Exclusive ring opening of the anti compound of a mixture of syn- and anti-1-methylbicyclo[2.2.1]heptene-2 in the presence of Ru-, Os-, Ir-, W-, and Re-based catalysts was observed116 proving that the exo face of norbomene is highly reactive while the endo face is inert toward metathesis. 

Murai et al. showed that the cycloisomerization of enynes catalyzed by PtCl2 has several feasible pathways (1) to 1,3-dienes via a formal metathesis, (2) to a 1,4-diene if the enyne substrates contains an allylsilane or stannane, (3) to a homo-allylic ether if it the reaction is performed in an alcoholic medium, or (4) to bicycle[4.1.0]heptene derivatives (Scheme 4) [26]. Further studies conducted by other groups have indicated the cyclization might proceed via a cationic mechanism triggered by coordination of Pt(II) with the alkyne moiety [27, 28]. Very recently, Oi and coworkers also observed a formal metathesis reaction mediated by a cationic Pt complex [29]. 

Olefin metathesis. Tungsten hexachloride with CjHjAlClj or n-butyllithium as cocatalyst has been used for olefin metathesis. Lithium aluminum hydride has been shown to be an effective cocatalyst and has the merit of availability and stability to air. Thus treatment of heptene-3 in chlorobenzene with WClfc-LiAIH for 3 hr. yields heptenc-3 (39%), octcnc-4 (23%), and hexene-3 (18.5%). A nonene, a pentcnc, and a butene were also formed in 10% yield. 

The first commercial metathesis polymer was polynorbomene, which was put on the market in 1976 by CdF-Chimie under the trade name Norsorex. The polymer is obtained by ROMP of norbomene (bicyclo[2.2.1]heptene-2) (eq. (19)) and gives a 90 % trans polymer with a very high molecular weight (> 3 X 10 g/mol) and a glass transition temperature (Tg) of 37 °C. 

The absolute stereochemistry of natural roseophilin was determined by means of asymmetric total synthesis by M.A. Tius and co-workers. The trisubstituted pyrrole moiety of the natural product was installed using the Paai-Knorr pyrrole synthesis starting from a macrocyclic 1,4-diketone. This diketone was prepared by reacting an exocyclic a, 3-unsaturated ketone with excess 6-heptenal in the presence of 3-benzyl-5-(hydroxyethyl)-4-methylthiazolium chloride as the catalyst. The major product was the trans diastereomer and the macrocyclization was achieved via aikene metathesis. It is worth noting that when the aldehyde was tethered to the cyclopentenone, all attempts to close the macrocycle in an intramolecular Stetter reaction failed. 

In order to show the catalytic activity of the W(CO)6/CCl4 based catalyst prepared in this study, the metathesis reaction of 1-heptene was investigated. The reaction products were identified by GC-MSD as described before, and given in detail elsewhere [13]. A... 

Figure 7, A representative mass chromatogram of the metathesis reaction products of 1-heptene with the photo-induced W(CO)6/CCL catalyst.

As shown in Table 3, the metathesis product of 1-heptene is a rather complex mixture of several compounds as reported in the related literature [10]. There is about 68% unconverted 1-heptene at the specific reaction conditions given before. The isomerization reaction products (i.e., 2-heptene and 3-heptene) are about 12%. 1-... 

TABLE 3. Relative amounts of metathesis products of 1-heptene determined by GC-MSD. 

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]. 

Figure 12. Metathesis of neat 1-hept-ene with Mof/MCM-41, Mop/MCM-48, and Mop/SBA-15. 1-heptene/Mo molar ratio = 1900, room temperature.

An alternative to the triolefin process produces hexenes, heptenes, and octenes along with ethene from propene by a three-step metathesis disproportionation. The product, containing hexene, heptene, and octene, has 95% linearity and will provide Cg, C7, or Cg cuts by fractionation or may be used as such in oxosynth-esis reactions for the production of polyvinyl chloride (PVC) plasticizers. Higher internal olefins for use in... 

Preparative-scale olefin metathesis of hept-3-ene, to give a mixture of hexene (14%), heptene (38%), and octene (20%), is described by Sammes and Matlin, using the tungsten hexachloride-lithium aluminium hydride reagent." Other synthetic applications of the olefin metathesis reaction have also been reported" " and reviewed." ... 

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