Cyclo-octatetraene derivatives

The triple bond of 6-phenyl-2-hexane [75] adds intramolecular ly to the phenyl ring to a cyclo-octatetraene derivative. The cycloaddition is a hundred times less efficient than in [74] and is found to be a singlet state reaction of the excited phenyl moeity. 

Studies have also been made of cyclo-octatetraene derivatives of the type (COT)Fe(CO)3 and (COT)[Fe(CO)3]2 [14], and solid and frozen solution data show that there is no appreciable change in the conformations of the molecules between the two phases [15]. 

Bis(cyclo-octatetraene) derivatives are also known for neptunium, plutonium, and protactinium. Np(CgH8)2 [133] and Pu(CgHg)2 [133] can be prepared via the following equations ... 

Dehydrobromination of (568) gave a low yield of the cyclo-octatetraene derivative as shown, and a transient cyclobutadiene seems a probable intermediate. Similarly, the trimer of 1,3-diphenylcyclobutadiene has been reported as a minor product of base-induced elimination from (569). ... 

For a monograph, see Fray Saxton The Chemistry of Cyclo-octatetraene and its Derivatives, Cambridge University Press Cambridge, 1978. For a review, see Paquette Tetrahedron 1975, 31, 2855-2883. For reviews of heterocyclic 8rr systems, see Kaim Rev. Chem. Interned. 1987, 8. 247-286 Schmidt Angew. Chem. Ini Ed. Engl. 1975, 14, 581-591 [Angew. Chem. 87, 603-613). 

The reduction of the benzenosulfene derivatives is independent of the nature of the electron donor and leads to the phenylthiolate ion (Todres 1980) (Scheme 2-18). However, the analogs containing the nitro group exhibit different behavior in reactions at the surface of the electrode and upon reductions by the cyclo-octatetraene dianion (Scheme 2-19). 

Alkynes undergo cycloaddition on irradiation with benzene or naphthalene derivatives or with other aromatic compounds. With a benzene derivative the product is usually a cyclo-octatetraene which results from thermal electrocyclic ring-opening of the bicyclo-octatriene formed initially by 1,2-addition of the alkyne to the benzene ring (equation 61) . The intermediate can be trapped using a dienophile such as tetracyanoethylene (equation 62) ". The first step of the photoaddition process involves excitation of the alkyne , and orbital symmetry considerations suggest that concerted 1,2-addition is allowed if the alkyne is excited but not if the benzene is excited ... 

In 1953 Jensen llfl) reported that the reaction between cyclo-octatetraene and K2(PtCl4) produced the complex (C8H8)PtCl2. He likewise described the iodo derivative, (C8H8)Ptl2. A tub conformation was postulated for the cyclooctatetraene ligand in these structures. Subsequent, detailed, infrared and NMR studies of these and analogous palladium complexes indicate substantial x-electron delocalization t05). 

One of the most intriguing successes of simple MO theory is the prediction of nonexistence of a number of jt-electron systems. Chemical existence is a very difficult notion which includes thermodynamic and kinetic requirements 108), so that predictions obtained from MO theory must be interpreted rather cautiously. Since it is assumed that -electron systems are planar (or nearly so), any considerable deviation from planarity can alter the theoretical predictions. For example, cyclo-octatetraene (which is predicted to be a rather unstable compound) and its derivatives are well defined compounds, but have nonplanar (a puckered T>2a tub ) conformation io9,no) it is this escape from planarity which makes cyclooctatetraene a stable compound. Other compounds, may exist as highly reactive species, as is the case with cyclobutadiene iii.ua) and its derivatives 118>. 

G. I. Fray and R. G. Saxton, The Chemistry of Cyclo-octatetraene and Its Derivatives, Cambridge University Press, Cambridge, 1978. 

Bender and his coworkers " have examined the influence of the position of a cyano substituent on the outcome of the reactions of the naphthalene derivatives 237, 238 and 239. Typical of the reactions is the direct irradiation (A > 290 nm) of 237, resulting in its conversion into the three products shown in Scheme 16. The semibullvalene 240 is also photochemically reactive and is converted into the cyclo-octatetraene in 75% yield on fur-... 

In a study of the cathodic reduction of cyclo-octatetraene in DMF and DMSO, Allendoerfer and Rieger used cyclic voltammetry and a.c. polarography to show that the reduction to the radical anion is quasi-reversible with a rate constant, ky, equal to 8.5 x 10" cm s at 25°C. The heat of activation was found to be 7.7 kcal mol" and the small values of a which were observed were interpreted in terms of the transition state at the equilibrium potential resembling the product radical anion more closely than it resembles the reactant molecule. The transition state is therefore presumably planar, as is the radical anion. This conclusion is supported by the similarity of the experimental value for the free energy of activation to the literature derived values for the free energy of activation in the bond isomerisation reaction of cyclo-octatetraene. 

Syntheses have been reported of barrelene (505) and of Nenitzescu s hydrocarbon (503) on a reasonable scale and without some of the difficulties that attend the previously published routes." " The preparation of (503) is of central importance, it being obtained by the oxidative bisdecarboxylation of the cyclo-octatetraene-maleic anhydride Diels-Alder adduct (502) with dicarbonylbis(triphenylphosphine)-nickel in diglyme at reflux. Cycloaddition of (503) to 2,5-dimethyI-3,5-diphenyl-cyclopentadienone in hot benzene afforded (504) and its endo-isomer. Photolysis of (504) yielded (505) in 24% yield from cyclo-octatetraene. The thermally labile benzene-maleic anhydride [4 + 2] cycloadduct (506) was obtained in similar fashion from (502). A review of the mechanisms of pyrolysis of (503) and a number of isomers and benzo-fused (CH) derivatives (collectively termed Nenitzescu s hydrocarbons) has appeared." ... 

Heptacyclo[8,6,0,0 , 0 , 0 ,0 ,0 ]hexadecane (697) together with the known 3,14-ethanodiamantane (ratio 1 4) are the products of AlBtj-Bu Br treatment of a hydrogenated C Hjo dimer of cyclo-octatetraene. Bromination of (697) with boiling bromine gave the 5-bromo-derivative, whose structure was verified... 

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