Cyclooctatetraene 1,3,5-Cyclooctatriene

Is cyclooctatetraene aromatic To tell, compare the first and second hydrogenation energies, leading to 1,3,5-cyclooctatriene and then to 1,3-cyclooctadiene. (The energy for hydrogen is provided at left.)... 

How might you use the Hofmann elimination to accomplish this reaction How would you finish the synthesis by converting cyclooctatriene into cyclooctatetraene ... 

Cyclooctatetraen kann elektrochemisch zum Cyclooctatetraenyl-Dianion reduziert werden. In waBrigem Alkohol bzw. DMF bildet sich mit bis zu 92% Umsatz (bei -2,1 V) hauptsachlich Cyclooctatrien-(l,3,5). Dagegen kann bei niedrigeren Kathodenpotentialen (auBer in reinem DMF) der Anteil des isomeren Cyclooctatriem-(1,3,6) auf bis zu 67% steigen4. 

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... 

Although a few other acyclic examples of stereospecific isomerisation of hexatrienes are known, specially in the field of natural product like steroid chemistry, the commonest reactions of this type are in cyclic hexatrienes. Cyclooctatriene and cyclooctatetraene are systems in which the electrocyclic reaction goes very readily and they show an interesting trend. 

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... 

Cyclooctatetraene was reduced electrochemically to cyclooctatetraenyl dianion. In DMF the product is mostly (92%) 1,3,5-cyclooctatriene at —1.2 V. If the potential is lowered the main product is 1,3,6-cyclooctatriene. Previous experiments, in which the anion radical was found to be disproportionated, were explained on the basis of reactions of the cyclooctatetraene dianion with alkali metal ions to form tightly bound complexes, or with water to form cyclooctatrienes. The first electron transfer to cyclooctatetraene is slow and proceeds via a transition state which resembles planar cyclooctatetraene102. 

Let us compare anion-radicals with dianions, which are definitely stronger bases. For example, the cyclooctatetraene dianion (CgHg ) accepts protons even from solvents such as dimethylsulfoxide (DMSO) and V,V-dimethylformamide. The latter is traditionally qualified as an aprotic solvent. In this solvent, the cyclooctatetraene dianion undergoes protonation resulting in the formation of cyclooctatrienes (Allendoerfer and Rieger 1965) + 2H+ CgHjo. It is seen that... 

Cyclooctatetraene (continued) with iron, 12 267-273 with nickel, 12 307, 308 with palladium, 12 315 with platinum, 12 319 with rhodium, 12 304 with ruthenium, 12 280 with silver, 12 340, 342, 343, 346 complexes of, 4 81 iron complexes of, 4 89 Cyclooctatriene complexes... 

From the cyclooctatriene - bicyclooctadiene equilibrium, it is possible to trap the structure containing the four-membered ring with dienophiles, e.g. maleic anhydride, including those cases where the bicyclic isomer is only present in small amounts. For example, the dimer of cyclooctatetraene 7 on reaction with maleic anhydride gives the 1 1 adduct 8 in refluxing benzene and the. n 7-tricyclo[4.2.0.02,5]oclane derivative 9 in refluxing toluene.62... 

This inversion barrier is much lower than that observed for derivatives of cyclooctatetraene (see Section X,B), and recognition that the fluorinated ring in complexes 119 may more closely resemble a cyclooctatriene than a cyclooctatetraene provides one rationale for the difference in its dynamic behavior compared to its rj1 -heptafluorocyclooctatetraeny 1 relatives. 

Mixtures of 1,3,5- and 1,3,6-cyclooctatriene were obtained by partial reduction of cyclooctatetraene in ways such as protonation of cyclooctatetraene dianion3d-4 and reduction with zinc-alkali.2 5 1,3,6-Cyclooctatriene is the major product in these reductions. However, since 1,3,6-cyclooctatriene isomerizes to 1,3,5-cyclooctatriene on treatment with base, quenching cyclooctatetraene dianion with methanol and subsequent heating affords 1,3,5-cyclooctatriene in an 80% yield.3d Reduction of cyclooctatetraene with sodium hydrazide and hydrazine also produces 1,3,5-cyclooctatriene.6 Therefore, when cyclooctatetraene is available in quantity, these procedures are the methods of choice. 

The final series of five procedures presents optimized preparations of a variety of useful organic compounds. The first procedure in this group describes the preparation of 3-BROMO-2(H)-PYRAN-2-ONE, a heterodiene useful for (4+2] cycloaddition reactions. An optimized large scale preparation of 1,3,5-CYCLOOCTATRIENE, another diene useful for [4+2] cycloaddition, is detailed from the readily available 1,5-cyclooctadiene. Previously, the availability of this material has depended on the commercial availability of cyclooctatetraene at reasonable cost. A simple large scale procedure for the preparation of 3-PYRROLINE is then presented via initial alkylation of hexamethylenetetramine with (Z)-1,4-dichloro-2-butene. This material serves as an intermediate for the preparation of 2,5-disubstituted pyrroles and pyrrolidines via heteroatom-directed metalation and alkylation of suitable derivatives. The preparation of extremely acid- and base-sensitive materials by use of the retro Diels-Alder reaction is illustrated in the preparation of 2-CYCLOHEXENE-1.4-DIONE, a useful reactive dienophile and substrate for photochemical [2+2] cycloadditions. Functionalized ferrocene derivatives... 

Schrauzer and Thyret have described (528, 529, 531) the synthesis of olefin-Ni(O) complexes containing a quinone, in particular, duro-quinone, as a ligand. The red, diamagnetic duroquinone complexes are obtained by reaction of nickel carbonyl with the quinone in excess olefin. They are stable in air and soluble in polar organic solvents and water. Those olefins which form the coiiqilex contain essentially parallel double bonds, e.g., norbornadiene, dicyclopentadiene, 1,5-cycloocta-diene, 1,3,5-cyclooctatriene, or cyclooctatetraene. 

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