Cyclooctatetraene dienes

The cyclooctatetraene-diene complex [( -C4H6)cot]Ti has been reported and has been shown by H NMR spectra to adopt an i -cw- ( -butadiene conformation. ... 

The Hiickel rule predicts aromaticity for the six-7c-electron cation derived from cycloheptatriene by hydride abstraction and antiaromaticity for the planar eight-rc-electron anion that would be formed by deprotonation. The cation is indeed very stable, with a P Cr+ of -1-4.7. ° Salts containing the cation can be isolated as a product of a variety of preparative procedures. On the other hand, the pK of cycloheptatriene has been estimated at 36. ° This value is similar to those of normal 1,4-dienes and does not indicate strong destabilization. Thus, the seven-membered eight-rc-electron anion is probably nonplanar. This would be similar to the situation in the nonplanar eight-rc-electron hydrocarbon, cyclooctatetraene. 

Abbreviations acac, acetylacetonate Aik, alkyl AN, acetonitrile bpy, 2,2 -bipyridine Bu, butyl cod, 1,5- or 1,4-cyclooctadiene coe, cyclooctene cot, cyclooctatetraene Cp, cyclopentadienyl Cp, pentamethylcyclopenladienyl Cy, cyclohexyl dme, 1,2-dimethoxyethane dpe, bis(diphenyl-phosphino)ethane dppen, cis-l,2-bis(di[Atenylphosphino)ethylene dppm, bis(diphenylphosphino) methane dppp, l,3-bis(diphenylphosphino)propane eda,ethylenediamine Et,ethyl Hal,halide Hpz, pyrazole HPz, variously substituted pyrazoles Hpz, 3,5-dimethylpyrazole Me, methyl Mes, mesityl nbd, notboma-2,5-diene OBor, (lS)-endo-(-)-bomoxy Ph, phenyl phen, LlO-phenanthroline Pr, f opyl py, pyridine pz, pyrazolate Pz, variously substituted pyrazolates pz, 3,5-dimethylpyrazolate solv, solvent tfb, tetrafluorobenzo(5,6]bicyclo(2.2.2]octa-2,5,7-triene (tetrafluorobenzobanelene) THE, tetrahydrofuran tht, tetrahydrothicphene Tol, tolyl. 

As is the case for [2 + 2] cycloaddition reactions (15-61), certain forbidden electrocyclic reactions can be made to take place by the use of metallic catalysts." An example is the silver ion-catalyzed conversion of tricyclo[4.2.0.0. ]octa-3,7-diene to cyclooctatetraene " ... 

In addition to cycloheptatriene, cyclooctatriene and cyclooctatetraene systems can be used as six-carbon components in the [6 + 2]-cycloaddition with 7t-systems (Scheme 36). Interestingly, in these cases, dienes react exclusively... 

The numerous transformations of cyclooctatetraene 189 and its derivatives include three types of structural changes, viz. ring inversion, bond shift and valence isomerizations (for reviews, see References 83-85). One of the major transformations is the interconversion of the cyclooctatetraene and bicyclo[4.2.0]octa-2,4,7-triene. However, the rearrangement of cyclooctatetraene into the semibullvalene system is little known. For example, the thermolysis of l,2,3,4-tetra(trifluoromethyl)cyclooctatetraene 221 in pentane solution at 170-180 °C for 6 days gave three isomers which were separated by preparative GLC. They were identified as l,2,7,8-tetrakis(trifluoromethyl)bicyclo[4.2.0]octa-2,4,7-triene 222 and tetrakis(trifluoromethyl)semibullvalenes 223 and 224 (equation 71)86. It was shown that a thermal equilibrium exists between the precursor 221 and its bond-shift isomer 225 which undergoes a rapid cyclization to form the triene 222. The cyclooctatetraenes 221 and 225 are in equilibrium with diene 223, followed by irreversible rearrangement to the most stable isomer 224 (equation 72)86. 

In systems of conjugated double bonds catalytic hydrogenation usually gives a mixture of all possible products. Conjugated dienes and polyenes can be reduced by metals sodium, potassium, or lithium. The reduction is accomplished by 1,4-addition which results in the formation of a product with only one double bond and products of coupling and polymerization. Isoprene was reduced in 60% yield to 2-methyl-2-butene by sodium in liquid ammonia [357]. Reduction of cyclooctatetraene with sodium in liquid ammonia gave a... 

Dienes. (+ )-Camphor-derived 1 H-, 2,4-triazole-3,5(2//,4//)-dione 24 was used to determine the absolute configuration of chiral cyclooctatetraenes of type 23 and ent-23 by cycloadduct formation (compare with 25 and 26) and X-ray analysis (see also p 446)166. 

Table 5. Bicyclo[4.2.0]ocla-2,4-dienes by Valence Isomerization of Cyclooctatetraene Derivatives...

VEELS studies have been made of the 1,3- and 1,5-cyclooctadienes and cyclooctatetraene adsorbed on Pt(lll) (260, 276). The spectra recorded at 170 K are consistent with rf interactions of the hydrocarbon with the surface (with spectra distinguishable from those of the 1,3- and 1,5-dienes themselves) involving losses of C = C groups. For cyclooctatetraene the... 

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