Cyclooctadiene results

The double-bond isomerization of cyclic materials possessing two double bonds takes place readily. When 1,4-cyclooctadiene is contacted with high-surface sodium on alumina at 0° for a short time, over 95% of the 1,3-cyclooctadiene results (IIS). However an even more interesting reaction takes place when the cyclic diolefin possesses a six-membered ring. An example is the reaction (D) of d-limonene which yields p-cymene and hydrogen (6). 

Conjugated dienes such as cyclopentadiene, 1,3-cyclohexadiene, and 1,3-cyclooctadiene result in the corresponding dihydrooxazine with a double bond in the alicyclic ring (70CB3242). Cycloaddition of the amidomethylium ion to norbornene takes place with exo selectivity (70CB3242). 

The reaction can be extended to other cycloalkenes such as cyclooctene, 1,5-cyclooctadiene, or 1,5-cyclooctadiene resulting in ozonides that have, in addition to the geminal 3-methyl-3-carbomethoxy substituents, a heptanal or cis-heptenal group at position 5 (in the case of 1,3-cyclooctadiene this side chain has the double bond in the non-conjugated position relative to the aldehydic group) <1993TL6591>. 

Bridged cyclooctadienes result from Cope rearrangement of fused substrates, following the theme seen in Scheme 12. A general route to the requisite substrates is the [2 + 2] cycloaddition of vinylketenes to cyclic 1,3-dienes, illustrated in equations (61) and (62) the vinylketenes may be formed by dehydroha-logenation of unsaturated acid chlorides or by thermolysis of cyclobutenones. ... 

The photosensitized dimerization of isoprene in the presence of henzil has been investigated. Mixtures of substituted cyclobutanes, cyclohexenes, and cyclooctadienes were formed and identified (53). The reaction is beheved to proceed by formation of a reactive triplet intermediate. The energy for this triplet state presumably is obtained by interaction with the photoexcited henzil species. Under other conditions, photolysis results in the formation of a methylcydobutene (54,55). 

The property of chirality is determined by overall molecular topology, and there are many molecules that are chiral even though they do not possess an asymmetrically substituted atom. The examples in Scheme 2.2 include allenes (entries 1 and 2) and spiranes (entries 7 and 8). Entries 3 and 4 are examples of separable chiral atropisomers in which the barrier to rotation results from steric restriction of rotation of the bond between the aiyl rings. The chirality of -cyclooctene and Z, -cyclooctadiene is also dependent on restricted rotation. Manipulation of a molecular model will illustrate that each of these molecules can be converted into its enantiomer by a rotational process by which the ring is turned inside-out. ... 

Kinetic studies using 1,9-decadiene and 1,5-hexadiene in comparison widi catalyst 14 and catalyst 12 demonstrate an order-of-magnitude difference in their rates of polymerization, widi 14 being the faster of the two.12 Furdier, this study shows diat different products are produced when die two catalysts are reacted widi 1,5-hexadiene. Catalyst 14 generates principally lineal" polymer with the small amount of cyclics normally observed in step condensation chemistry, while 12 produces only small amounts of linear oligomers widi die major product being cyclics such as 1,5-cyclooctadiene.12 Catalyst 12, a late transition metal benzylidene (carbene), has vastly different steric and electronic factors compared to catalyst 14, an early transition metal alkylidene. Since die results were observed after extended reaction time periods and no catalyst quenching or kinetic product isolation was performed, this anomaly is attributed to mechanistic differences between diese two catalysts under identical reaction conditions. 

Manufacture of rhodium precatalysts for asymmetric hydrogenation. Established literature methods used to make the Rh-DuPhos complexes consisted of converting (1,5-cyclooctadiene) acetylacetonato Rh(l) into the sparingly soluble bis(l,5-cyclooctadiene) Rh(l) tetrafluoroborate complex which then reacts with the diphosphine ligand to provide the precatalyst complex in solution. Addition of an anti-solvent results in precipitation of the desired product. Although this method worked well with a variety of diphosphines, yields were modest and more importantly the product form was variable. The different physical forms performed equally as well in hydrogenation reactions but had different shelf-life and air stability. 

Presumably, the stereoselectivity in these cases is the result of coordination of iridium by the functional group. The crucial property required for a catalyst to be stereodirective is that it be able to coordinate with both the directive group and the double bond and still accommodate the metal hydride bonds necessary for hydrogenation. In the iridium catalyst illustrated above, the cyclooctadiene ligand (COD) in the catalysts is released by hydrogenation, permitting coordination of the reactant and reaction with hydrogen. 

The gas chromatographic analysis of the unreacted monomers in the experiments from Table II discloses a constant C5/C8 ratio comparing the starting comonomer composition to the final composition. This means that monomer conversion is the same for 1,5-cyclooctadiene and cyclopentene in the copolymerization so that copolymer compositions are equal to the charge ratios. This result is consistent with the product analysis by 13C NMR spectroscopy where the copolymer composition is nearly identical to the starting comonomer composition. 13C NMR is used to determine the composition of the cyclopentene/1,5-cyclooctadiene copolymers as part of a detailed study of their microstructure (52). The areas of peaks at 29-30 ppm (the pp carbon from cyclopentene units) and at 27.5 ppm (the four ap carbons from the 1,5-cyclooctadiene) are used to obtain the mole fractions of the two comonomers (53, 54, 55). 13C NMR studies and copolymer composition determinations are described by Ivin (51, 56, 57) for various systems. 

Electrophylic halogenation of 9-oxabicyclo[3.3.l]nona-2,6-diene (139), a heteroanalog of 39, in the presence of water and its epoxidation with performic acid results in ring closure to 4,8-disubstituted 2,6-dioxaada-mantane derivatives.168 4,8-Dibromo-2,6-dioxaadamantane is also prepared from the syn-dibromide of 1,5-cyclooctadiene.169... 

If the insertion step following oxidative addition occurs on one of the two fragments resulting from oxidative addition, an intramolecular catalytic reaction (C—O — C—C rearrangement) takes place (example 40, Table III). It is interesting to note that two different products—2,6- and 3,6-heptadienoic acids—can be obtained from allyl 3-butenoate. Their ratio can be controlled by adding 1 mole of the appropriate phosphine or phosphite to bis(cyclooctadiene)nickel or similar complex. Bulky ligands favor the 2,6 isomer. It is thus possible to drive the reaction toward two different types of H elimination, namely, from the a or y carbon atoms. 

The GED results obtained for 1,3-cyclooctadiene should be regarded with caution, as the data in Table 7 refer to a 25-year-old study, where it was assumed that only one conformer is present. The structure of 1,3-cyclooctadiene should therefore be reinvestigated. 

Some typical results are shown in Table 2. The table shows that oxidation of conjugated dienes such as isoprene, piperylene (1,3-pentadiene), cyclopentadiene and 1,3-cyclohexadiene with a carbon anode in methanol or in acetic acid containing tetraethylammonium p-toluenesulfonate (EtjNOTs) as the supporting electrolyte yields mainly 1,4-addition products2. 1,3-Cyclooctadiene yields a considerable amount of the allylically substituted product. 

Pardey and coworkers159,161 also reported results for water-gas shift and nitrobenzene reduction for the related Rh complex, [Rh(COD)(amine)2](PF6), where COD = 1,5-cyclooctadiene, immobilized on P(4-VP), and results are reported in... 

From these results he assigned a cyclooctadiene formula to rubber, and concluded, in the tone of the times, that the rubber molecules combined through the action of "partial valence" into much larger aggregates (39). 

The mercuration-demercuration reaction of cw,cw-l,5-cyclooctadiene (3) has been widely studied in order to get some insight into the synthesis of 9-oxa and 9-azabicyclo-nonane derivatives. However, the results of the reaction have often been the subject of some controversy since the ratio of the two isomeric bicyclo[3.3.1]- [199 and 201] and [4.2.1]- [198 and 200] nonanes, after reduction (equation 166), strongly depended on the reaction conditions of the mercuration step168,169. 

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