Octene isomers

When 1-octene was the substrate and the reaction was carried out in CH3CO2D, no D appeared in the mixture of octene isomers. In order to determine whether the 2-octene formed was obtained via a 1,3 shift [Eq. (54)] or two cocurrent 1,2 shifts [Eq. (65)], the isomerization was carried out with 1-octene labeled in the 3 position, C5HuCD2CH=CH2. The 2-octene isolated was not labeled in the methyl group. Hence, Eq. 

Yields Nearly 80% conversion of n-butenes can be attained and se-lectivities toward octenes are about 85%. The typical C8 product is a mixture having a minimum of 98.5% octene isomers with the following distribution ... 

In our reaction scheme, however, low selectivities for olefins were observed because of the high extent of 1-octene oligomerization. During the first minute of reaction, the results showed for the high ten ierature of 623K, a 0.8 yield of 1-octene isomers (Fig.7). These in turn decreased rapidly to less than 1%, and then gradually started to rise to a final value of 20%. This explains ... 

Fig. 7 1-Octene isomers mole fraction at various feed compositions and temperatures.

Pyrolysis of trialkylboranes having eight or more carbons in the main alkyl chain gives bicyclic, as well as monocyclic, products (64). Tri- -octyl-borane loses two moles of hydrogen, giving 8-borahydrindane (LI II) in good yields the octene isomers have predominantly central C=C bonds. 

PROBLEM 15.36 Assign the IR spectra below to the correct octene isomer. Explain your reasoning. 

A highly diastereoselective alkcnylation of c/s-4-cyclopentene-l,3>diols has been achieved with 0-protected (Z)-l-iodo-l-octen-3-ols and palladium catalyst (S. Torii, 1989). The ( )-isomers yielded 1 1 mixtures of diastcrcomcric products. The (Z)-alkenylpalladium intermediate is thought to undergo sy/i-addition to the less crowded face of the prochiral cyclopentene followed by syn-elimination of a hydropalladium intermediate. 

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. 

Batch Experiments with Thermomorphic Systems. As a reference, we tested the hydroformylation of 1-octene in a completely homogeneous system using the same rhodium triphenylphosphine catalyst that is used for hydroformylation of lower aldehydes. This is sample R39 in Table 28.1, and gives us a baseline to compare the performance of our systems in terms of conversion and selectivity. To maintain consistency, we performed all the reactions at 100°C using the same amounts of reactants, catalysts and solvents. Under these conditions we only detected aldehyde products no alcohol or alkene isomers were formed. 

The first few experiments in the continuous flow reactor yielded inconsistent octene conversions (Figure 28.3). The experiment ran for 218 hours. Initially the conversion was consistent at 3-4% for several hours, then improved significantly to 16% and then rapidly dropped off to less than 2% (Figure 28.3). The selectivity was also very good for this ran, with an average normal to branch isomer ratio of 7 1. 

The ligands synthesized were also apphed to the isomerizing hydroformylation of more reactive 2-pentene. At 120 °C/ 20 bar quantitative conversion of olefin to aldehydes was achieved within 40 min. Trends similar to those described for internal octene hydroformylation were found. The regioselectivity obtained for the individual ligands tends to be 5% higher compared to that for the octenes. Thus, in the presence of 10 75% of n-hexanal were determined, compare Table 3. Obviously, 2-pentene is able to react more smoothly to the terminal isomer compared to olefins having the double bond in an more internal position. Illustrative for this effect are also literature results obtained for 2- and 4-octene.4,5... 

Ligand to rhodium ratio is 10, catalysis performed at 80 °C, in 13 ml of toluene using 1 ml of 1-octene (plus 1 ml of 1 -nonanal entries 2 and 4). Samples were analysed by means of GC and GC-MS analysis. b Entries 1, 3, and 5 50 bar syn gas. Entries 2 and 4 50 bar H2.c Numbers include isomers of 1-octene since these are not separable from octane on GC. 

Another important feature of this reaction is the synthesis of highly strained E-cycloalkenes. Thus E,Z-cycloocta-1,3-diene has been obtained from the Z,Z-compound in sensitized irradiation 309) (3.4), while E-cyclo-octene was obtained from the Z-isomer by direct irradiation (3.5) 310). The synthesis of a trans doubly bridged olefin has also been reported (3.6)311>. 

Further progress in providing linear aldehydes from olefinic substrates has been provided by modified rhodium catalysts. Without modifiers, the product from the hydroformylation has very low normal iso isomer ratios 1-octene gave only 31% of the linear isomers in one example (28). 

The strained c ,traws-l,3-cyclooctadiene 1 cyclizes quantitatively at 80 °C to the bicy-clo[4.2.0]octene 2 (equation 3). The higher homologue 3 exists in equilibrium with the bicyclic isomer 4 above 175 °C (equation 4)4. 

The formation of derivatives of 2,3,6,8-tetraazabicyclo-[3.2.1]3-octene (425) arises from an intramolecular nucleophilic addition to the nitrone group of hydra-zone (424). Compound (424) was prepared by reaction of 2-acyl-3-imidazoline-3-oxides (423) with hydrazine. From the cis- and frans-derivatives (424), exo- and enr/o-isomers (425) were obtained (Scheme 2.197). The reaction of intramolecular cyclization does not occur in cases with monosubstituted hydrazones (316). 

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