Cyclo-1,3,5,7-octatetraene

Photochemical and thermal reactions of cyclo-octatetraene are discussed in a review on (CH) hydrocarbons the reversible rearrangement of 1,2-dimethylcyclo-octatetraene to the 1,6-isomer in a flow system at 600 °C is reported.  

Addition of chlorine to cyclo-octatetraene is unusually fast and gives exclusively the cis-1,2-dichloride, presumably via (295) the latter can be efficiently obtained as a hexachloroantimonate by reaction of cyclo-octatetraene with antimony pentachloride. The tetrafluoroborate of (295) can be converted into (296) in a first-order inversion which is strongly catalysed by cis-7,8-dichlorocyclo-octa-l,3,5-triene.  

Protonation of methoxycyclo-octatetraene gives (297), which rearranges on warming to (298) deuterium-labelling studies are interpreted in terms of a rearrangement via (299).  

Addition of sulphur dioxide to cyclo-octatetraene in the presence of antimony pentafluoride gives the homotropylium ion (300), which on reaction with water produces (301). Addition of iodine azide and sodium azide to cyclo-octatetraene gives the diazide (302), which is in equilibrium with the bicyclo- 

Compound (303 X = F) is reduced by sodium hydride-hexamethylphos-phoramide to give (304) various cycloadditions and organometallic reactions of (303) are also reported.  

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Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

While (Z)-l,2-bis(phenylsulfonyl)ethylene (140) does not add to dienes such as furan, cyclopentadiene, cyclo-octatetraene, indene and /f-naphthol, ( )-l,2-bis(phenylsulfonyl)ethylene (141) is more reactive and the reaction with furan proceeds at room temperature for 2 h to give the adduct in 95% yield. The reactivity of dienophiles having sulfonyl group in the [4 + 2]cycloaddition is shown in equation 10393,101. 

WUlstatter, R. Waser, E. (1911) Uber Cyclo-octatetraen. Berichte der Deutschen Chemischen Gesellschaft, 44, 3423-3445. 

Benzyne reacts with benzene to give a mixture of products in low yield. The original experiments 38> showed that the 1,4-cyclo-adduct (benzo-barrelene) (19), the valence-bond isomerised 1,2-cyclo-adduct (benzo-cyclo-octatetraene) (20), and the product of insertion into a carbon-hydrogen bond (biphenyl) (21), were obtained in 2,8, and 6% yields respectively. 

For the synthesis of the bis-cyclo-octatetraene compound [5] (Krummel et al, 1987 Auchter-Krummel and Mullen, 1991), cyclo-octatetraene dianion was quenched with tetrabromoneopentane to give the bis-adduct [23], which exists in an equilibrium between valence isomers [23a] and [23b]. Hexacycle [23a] was actually isolated in about 60% yield (Fig. 2) (Krummel et al, 1987). Accordingly, in the subsequent dehydrogenation, the formation of [23a] must be avoided by working at low temperatures in this case it was possible to deprotonate the originally formed isomer [23b], obtaining a... 

Cycloocta-2,5-diene yields the mono adduct with dimethylvinylidene carbene ( 19%) [156]. With dichloro- and dibromocarbene, the syn- and cmh-bis-adducts are obtained in a ratio which favours the syn-isomer [55, 104] whereas, with bromochlorocarbene, the mono-adduct is reported to be the major product (55%) with only 9% of the bis-adduct [142]. In contrast, cyclo-octatetraene is converted into the mono-, syn-1,2 5,6-bis-, tris-, and tetra-adduct with dichlorocarbene depending on the reaction conditions [4, 17, 25, 55] and the 1,2 5,6-bis-adduct with... 

Cyclohexa-1,3-diene is readily hydrogenated to cyclohexene, but cycloheptatriene is hydrogenated more slowly to give a mixture of cycloheptene and cyclohepta-1,3-and 1,4-diene. Further hydrogenation of the conjugated diene is extremely slow. Cyclohepta-1,4-diene and cyclo-octatetraene are not hydrogenated. 

Avram et al. (1964) have reported the preparation of the tricyclic systems shown below and their thermal isomerizations. Both isomers yield cyclo-octatetraene at temperatures above 100° C. Compound I isomerizes to cyclo-octatetraene with a half life of about 20 minutes... 

The point for cyclo-octatetraene dianion was not used in determining the slope because of uncertainty about the magnitude of its ring current and extent of dissociation. 

Common examples of systems often mistaken as being aromatic (because of their alternating double and single bonds) are cyclobutadiene and cyclo-octatetraene (shown in Figure 6-9). In the case of cyclobutadiene, 4n + 2 = 4, giving n = 0.5, while for cyclooctatetraene, 4n + 2 = 8, so that n = 1.5. In these two compounds, n is not an integer, so these systems are anti-aromatic (nonaromatic). Anti-aromatic systems (non-Hilckel systems) are less stable than aromatic or normal systems. 

Mercuric acetate, reaction with cyclo-octatetraene, 50, 24 Mercuric oxide, use in oxidation of hydrazones, 50, 28 with 3-chlorocyclobutanecarboxylic acid and bromine to give 1-bromo-... 

The synthesis of bis(rj8-cyclooctatetraene)uranium(IV) (uranocene)J from uranium tetrachloride and (cyclooctatetraene)dipotassium was first published in 1968.1 The method reported here is a modification of that procedure and is suitable for a large variety of cyclooctatefraene complexes.2-4 BisO 8-cyclo-octatetraene)uranium(IV) has also been prepared by the reaction of uranium tetrafluoride with (cyclooctatetraene)magnesium in the absence of solvent.5 Direct reaction of finely divided uranium metal with cyclooctatetraene vapors at 150° also gives some uranocene.5 However, both methods give low yields. 

Cyclo-octatetraene reacts with iron carbonyls to form complexes with the compositions [Fe(CO)3(C8H8)], [Fe2(CO)6(C8H8)], and [Fe2(CO)7(C8H8)] 152, 168, 180). Nakamura and Hagihara 166) report that the complex [Fe(CO)3(C8H8)] decolorizes bromine in carbon tetrachloride and shows absorption bands in its infrared spectrum at 699, 716, and 720 cm-1 due to cis-double bonds. They suggest structure (XVI) for this complex, i.e., the hydrocarbon retains its tub form in the complex. These results are con-... 

A single crystal X-ray structural determination of the binuclear complex [Fe2(CO)6(C8H8)] (64a) shows it to have the structure (XVIII) and not one of the previously suggested structures 22, 54,152,166,174) including tub and planar forms of the cyclo-octatetraene ring. The cyclo-octatetraene ring in the complex approximates to a chair form in which the four carbon atoms associated with each iron atom are planar or very nearly so. The observed Fe—C and C—C distances in this complex are compared... 

The compound cyclopentadienylcyclo-octatetraenecobalt is probably analogous to the compound cyclopentadienyl cyclopentadienecobalt (XXIV). The cyclo-octatetraene residue shows two proton resonance lines in the nmr spectrum (167) in contrast to that in the iron complex [Fe(CO)3(cyclo-octatetraene)] which shows only one proton resonance line (152, 180). 

Anhydrous silver-olefin complexes are readily dissociable, low-melting, and variable in composition 92a, 176, 183). Cyclic olefins and polyolefins form stable complexes with silver nitrate or perchlorate, but again the Stoichiometry of the complexes varies considerably, sometimes depending on the conditions of preparation. The following types have been isolated [Ag(un)2]X (un = e.g., cyclohexene, a- and /3-pinene) ISO), [Ag(diene)]X diene = e.g., dicyclopentadiene 220), cyclo-octa-1,5-diene 50, 130), bi-cyclop, 2,1 ]hepta-2,5-diene 207), and cyclo-octa-1,3,5-triene 52), and [Ag2(diene)]X2 (diene = e.g., cyclo-octa-1,3- and -1,4-diene 180), bi-cyclo[2,2,l]hepta-2,5-diene 1) and tricyclo[4,2,2,0]-decatriene 10)). Cyclo-octatetraene (cot) forms three adducts with silver nitrate 52), viz., [Ag(cot)]NOs, [Ag(cot)2]N03, and [Ag3(cot)2](N03)3. On heating, the first two lose cyclo-octatetraene and all three decompose at the same temperature. From the stoichiometry of the above complexes it appears that the... 

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