Cis,trans- 1,5-cyclooctadiene

HOMO-LUMO energy difference in ethylene is greater than that of cis trans 1 3 cyclooctadiene... 

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 ... 

Time, hr Bicyclo[4.2.0]-oct-7-ene, mole % cis,trans-1,3-Cyclooctadiene, mole % cis,cis-1,4-Cyclooctadiene, mole %... 

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 ... 

The energy of electromagnetic radiation is inversely proportional to its wavelength. Since excitation of an electron for the tt — rr transition of ethylene occurs at a shorter wavelength (Amax = 170 nm) than that of cis, trans- 1,3-cyclooctadiene (Amax= 230 nm), the HOMO-LUMO energy difference in ethylene is greater. 

Figure 13.37 shows the UV spectrum of the conjugated diene cis,trans- 1,3-cyclo-octadiene, measured in ethanol as the solvent. As is typical of most UV spectra, the absorption is rather broad and is often spoken of as a band rather than a peak. The wavelength at an absorption maximum is referred to as the max of the band. There is only one band in the UV spectrum of 1,3-cyclooctadiene its kmax is 230 nm. In addition to max, UV-VIS bands are characterized by their absorbance (A), which is a measure of how much of the radiation that passes through the sample is absorbed. To correct for concentration and path length effects, absorbance is converted to molar absorptivity (e) by dividing it by the concentration c in moles per liter and the path length / in centimeters. 

The new technique is convenient for synthesis of pure trans -cyclooctene. The oxide of cw-cyclooctene (4) is converted into trans-cydoocteae (7) in > 90% yield, > 99.5% isomeric purity.3 Rigorously aprotic conditions are required for stereoselectivity. In the same way tram-1 -methylcyclooctene, cis.trans-1,4-cyclooctadiene, and cis.trans-1,5-cyclooctadiene have been prepared from the corresponding epoxides. 

The fused cyclobutenes prefer a path which leads to disallowed cis, cis cyclic diene. Thus bicyclo-octane(IV) opens at 230°-260°C to give cis, cis 1,3 cyclooctadiene and not cis-trans diene. 

However, as the temperature rises this is rapidly converted to the TT-allylic complex. Similar complexes of conjugated dienes involving complexing of only one double bond have been observed with trans-1,3-pentadiene, cis,trans-2, i-hexadiene, and 1,3-cyclooctadiene. 

Haight and co-workers (269) have found that crystalline complexes can be readily obtained by reduction of CuCl2-2H20 or CuBr2 dissolved in ethanol with sulfur dioxide in the presence of the di- or oligoolefin. By this method they have prepared 1 1 complexes with norbomadiene, 1,5-cyclooctadiene, cyclooctatetraene, and dicyclopentadiene, 1 2 complexes with cis,trans,trans- and aW-complex with 1,3-cyclooctadiene. It was noted that rapid addition of SO2 to the system produced 1 2 complexes with norborna-diene and cyclooctatetraene. 

Cyclohexane and neohexene are converted to benzene and neohexane in the presence of [IrH2(Me2C0)2(PRj)2] bFe. Without neohexene, benzene and two equivalents cyclohexane are produced. The mechanism (Scheme 2A)is based on the isolated complexes (A) and (B). 1,5-cyclooctadiene is slowly converted to cyclooctene by Rhg(C0)ig in isopropanol, probably isomersiation to 1,4- and 1,3-cyclooctadiene.The oxidation of cis-(24) by cyclohexenone in the presence of RhH(PPhj)ij is faster than of trans-(24) due to steric interactions... 

Butadiene could be oligomerized to cyclic dienes and trienes using certain transition metal complexes. Commercially, a mixture of TiCU and Al2Cl3(C2H5)3 is used that gives predominantly cis, trans, trans-1,5,9-cyclododecatriene along with approximately 5% of the dimer 1,5-cyclooctadiene ... 

Homogeneous nickel complexes proved to be versatile catalysts in dimerization and trimerization of dienes to yield different oligomeric products.46-55 Depending on the actual catalyst structure, nickel catalyzes the dimerization of 1,3-butadiene to yield isomeric octatrienes, and the cyclodimerization and cyclotrimerization to give 1,5-cyclooctadiene and all-trans-l,5,9-cyclododecatriene, respectively46 56 [Eq. (13.13)]. Ziegler-type complexes may be used to form cis,trans,trans-1,5,9-cyclododecatriene37,57 58 [Eq. (13.14)], which is an industrial intermediate ... 

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