1,3-cyclooctadiene, isomerization

Isonurization of dienes. This strong base effects isomerization of 1,5- or 1,3-cyclooctadiene to cij-bicyclo[3.3.0]-A -octene (5) in 50-65% yield (stirred in an autoclave at 175° for 22 hrs.). In the case of 1,3-cyclooctadiene, isomerization to... 

Tetrachloropalladate(II) ion catalyzes the interconversion of 1- and 2-butenes in aqueous solutions containing chloride and hydronium ions. Sodium tetrachloropalladate(II) catalyzes the conversion of allylbenzene to propenyl-benzene in acetic acid solutions. Tetrakis(ethylene))Lt,/x -dichlororhodium(l) catalyzes butene isomerization in methanolic hydrogen chloride solutions . Cyclooctadienes isomerize in benzene-methanol solutions of dichlorobis-(triphenylphosphine)platinum(11) and stannous chloride. Chloroplatinic acid-stannous chloride catalyzes the isomerization of pentenes. Coordination complexes of zero-valent nickel with tris(2-biphenylyl)phosphite or triphenyl-phosphine catalyze the isomerization of cis-1,2-divinylcyclobutane to a mixture of c/5,m-l, 5-cyclooctadiene and 4-vinylcyclohexene . Detailed discussions of reaction kinetics and mechanisms appear in the papers cited. 

Borabicyclo [3.3.1] nonane [280-64-8], 9-BBN (13) is the most versatile hydroborating agent among dialkylboranes. It is commercially available or can be conveniendy prepared by the hydroboration of 1,5-cyclooctadiene with borane, followed by thermal isomerization of the mixture of isomeric bicychc boranes initially formed (57,109). 

Photolytic reactions of dienes frequently give complex mixtures of rearranged products. Described here, however, is a photolytic isomerization of 1,5-cyclooctadiene (present in solution, in part, as a complex with cuprous chloride) that affords a good yield of one product. 

A recent study of Murov and co-workers<106) indicates that the activation energies for isomerization are not the controlling factors. Thus the fluorescence of naphthalene is quenched (5 x 108M-1sec-1) by cis-trans-1,3-cyclooctadiene with isomerization to form cis-cis-1,3-cyclooctadiene. However, the compound bicyclo[4,2.0]oct-7-ene is not formed despite the low activation energy for this process ... 

In many cases the transformations may be more complex than indicated by Eqs. (9.89)-(9.100). An example of this is the photochemistry of cis,cis-1,3-cyclooctadiene [Eq. (9.94)].<169) A close examination of this reaction indicates that bicyclo[4.2.0]oct-7-ene is formed but in low relative yields during the initial reaction (see Table 9.9). In addition, the cis,trans-1,3-cyclooctadiene is formed and then consumed as the reaction proceeds. Fonken showed that the bicyclooctene initially formed, however, was not from thermal isomerization of the cis,trans-diene. Still a third reaction was the 1,3 sigmatropic hydrogen shift to form the cis, cis-1,4-cyclooctadiene ... 

Thus the range of bicyclic peroxides available via peroxymercuration may be quite limited. Nevertheless where the method works best, namely with 1,5- and 1,4-cyclo-octadiene, it makes a valuable contribution in that each peroxymercuration is regiospecific and leads to a dioxabicyclodecane that is isomeric with the [4.2.2] compound 23 available via photooxygenation (Eq. 18). Furthermore, the [3.3.2] compounds derived from 1,5-cyclooctadiene are, to the best of our knowledge, the only bicyclic peroxides obtained to date that do not contain either a 5- or a 6-membered dioxacycloalkane ring. 

There is an absence of cis-to-trans isomerization with conversion or time for the C8 (1,5-cyclooctadiene) polymer. This is shown from 52 to 58% conversion after 1 to 16 hours reaction time in Table II and III. The above review (A0, A2, A3, A5) shows that the cis structure in polymers from 1,5-cyclooctadiene using various chloride catalysts fell below 50% cis even to 20% cis units this means that the second cis double bond from the monomer underwent extensive cis-to-trans isomerization following the ring-opening of the first cis bond. Where cis-2-butene isomerizes to trans structure using other catalyst preparations, there is no evidence of this for cis-2-butene using the iodine system. However, polymer molecular... 

In 1968, while investigating the efficacy of bis(rj-cyclopentadienyl)-diphenyltitanium as a catalyst for the isomerization of 1,5-cyclooctadiene to 1,3-cyclooctadiene, Hagihara and co-workers found that the presence of CO inhibited the isomerization. Under the reaction conditions imposed, Cp2Ti(CO)2 (1) and benzophenone were isolated. Furthermore, 1 showed poor catalytic activity for this isomerization (34). 

The thermolysis of ladderanes has been studied in detail (Scheme 1). On heating, bicyclo[2.2.0]hexane and its derivatives exhibit skeletal inversion and cleavage to 1,5-hexadiene derivatives.26 The thermolysis of anti- and yyft-tricyclo[4.2.0.02,5]octanes and their derivatives gives cis,cis- and cis, trans-1,5-cyclooctadienes, cis- and trans-1,2-divinylcy clobutanes, and 4-vinylcyclohexene as ring-opening products.27-29 Furthermore, syn-tricyclo-[4.2.0.02,5]octane isomerizes to aw//-tricyclo[4.2.0.02,5]octane.29c,d The thermodynamic parameters and the reaction mechanisms for these thermal reactions have been discussed. 

The thermal isomerization of syn-2 has been studied in detail.68 When a solution of syn-2 in decahydronaphthalene was heated at 220 °C, it isomerized to anti-2 quantitatively (Scheme 15). When anti-2 in decahydronaphthalene was likewise heated at 220 °C, no isomerization of anti-2 to syn-2 was observed, and anti-2 was recovered. The thermolysis pathway is partially dilferent from that of the corresponding ladderane syn-tricyclo[4.2.0.02,5]octane was reported to give 1,5-cyclooctadienes, anti-tricyclo[4.2.0.02,5]octane, and 1,2-divinylcyclobutanes in 51, 41, and 8% yields, respectively.29c,d... 

From a consistent set of hydrogenation enthalpies in glacial AcOH, the cyclooctadi-enes decrease in stability 1,5- (29) < 1, 4- (56) < 1,3- (55a) with sequential differences of 13.0 (29, 55a) and 6.7 (55a, 56) kJmol-1. For comparison—despite our earlier enunciated skepticism about isomerization reactions performed in polar media (Z-BuOK in DMSO) — the following enthalpies of reaction, and thus enthalpies of formation, differences were found43 16.4 1.4 and 2.8 0.8 kJmol-1. Consistency, if not precise numerical agreement, is found for the energetics of the isomeric cyclooctadienes. 

By the end of the 1970s, PdCl2(PPh3)2 was being used to hydrogenate 1,5-cy-clooctadiene [10]. The substrate isomerization to 1,3-cyclooctadiene preceded its... 

Cyclooctadiene isomers (i.e., 1,5-cod or 1,3-cod) are selectively hydrogenated by [Ru(/74-cod)(/76-C8H1o)] (51) to produce exclusively cyclooctene in THF, under ambient temperature (20 °C) and 1 bar H2 pressure [64]. Again, cyclooctane is only detected when the diene substrate is completely transformed to the monoene. The rate of hydrogenation is higher in case of the conjugated 1,3-cycloocta-diene substrate, whereas isomerization of the non-conjugated 1,5-cyclooctadiene... 

In this context, the striking difference of the standard 70 eV El mass spectra of the isomeric cyclooctadienes may be mentioned here (see below)87. Whereas the radical cations of the stereoisomeric 1,5-cyclooctadienes, containing two bis-allylic C—C bonds, give the products of the two-fold allyl cleavage as the base peak ([C4H6]+ /[M]+ s=ss 10 1), the cis,cis-l,4 and cis.cis-].3-cyclooctadicnc ions are reluctant to do so (IC4II511 / [M]+ 1 3). Clearly again, 1,2- and 1,3-H shifts cannot efficiently compete with dissociation of the bis-allylic C—C bond. 

Cyclooctadienes, Cyclooctatrienes and Cyclooctatetraene. As mentioned in Section III.E, the 70 eV El mass spectra of the isomeric cyclooctadienes are strikingly different87. Not surprisingly, the three possible stereoisomeric 1,5-cyclooctadienes give similar spectra, the product ions C4H6+ of the apparent [4 + 4] cycloreversion, i.e. loss of... 

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. 

Dihydromesitylene likewise gives a 1,3 complex (34) and 1,4-cyclohexadiene gives 1,3-cyclohexadieneiron tricarbonyl. 1,5-Cyclo-octadiene on treatment with catalytic quantities of Fe(CO)g gives 1,3-cyclooctadiene (35), as the iron tricarbonyl complex is probably not very stable and is continuously displaced by fresh 1,5-diene until isomerization is complete. 

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). 

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