Cyclooctatetraene reactant

If the cycloaddition and cycloreversion steps occurred under the same conditions, an equilibrium would establish and a mixture of reactant and product olefins be obtained, which is a severe limitation to its synthetic use. In many cases, however, the two steps can very well be separated, with the cycloreversion under totally different conditions often showing pronounced regioselectivity, e.g. for thermodynamic reasons (product vs. reactant stability), and this type of olefin metathesis has been successfully applied to organic synthesis. In fact, this aspect of the synthetic application of four-membered ring compounds has recently aroused considerable attention, as it leads the way to their transformation into other useful intermediates. For example aza[18]annulene (371) could be synthesized utilizing a sequence of [2 + 2] cycloaddition and cycloreversion. (369), one of the dimers obtained from cyclooctatetraene upon heating to 100 °C, was transformed by carbethoxycarbene addition to two tetracyclic carboxylates, which subsequently lead to the isomeric azides (368) and (370). Upon direct photolysis of these, (371) was obtained in 25 and 28% yield, respectively 127). Aza[14]annulene could be synthesized in a similar fashion I28). 

From a purely synthetic viewpoint, triazolinedione adducts have served as substrates for gaining access to numerous target molecules such as prismane, semibullvalene, bridged semibullvalenes, elassovalene, caged compounds, and azoalkanes. Indeed, the title reagent can be used not only as a chiral source, but also as an azo donor. In the synthesis of 4,5-diazatwis-4-ene, for example, (-)- nfirst step involved cycloaddition to cyclooctatetraene dibromide with formation of a separable mixture of diastereoisomers. Eventual removal of the... 

A triplet-sensitized photoreaction in the crystalline state has been achieved by using crystalline organic salts which were prepared from cationic sensitizers and an anionic reactant (Scheme 40) [73]. Thus, upon selective excitation of the sensitizer these salts or hydrogen-bonded complex gave two dibenzosemi-bullvalenes through triplet-triplet energy transfer to the reactant, A dibenzo-cyclooctatetraene, which is a product of direct (singlet state) irradiation, was not produced. 

Another kind of tetraradicaloid Cl has been invoked and computationally characterized for photoisomerization of cyclooctatetraene. Photoexcitation leads to return to reactant, double-bond shift, and formation of semibullvalene. The tetraradicaloid... 

Chelating olefins such as cycloocta-1,5-diene, cyclooctatetraene, or dicyclopentadiene have not yielded isolable complexes by direct reaction with nickel carbonyl, probably for reasons outlined in Section III, B. From this it should not be concluded that such complexes are incapable of existence. Using reactions in which nickel carbonyl is not the reactant it has been possible to prepare not only complexes of cyclooctadiene and cyclooctatetraene, but also of simple monoolefins (Section IX). 

A detailed kinetic investigation of the reaction of [Ru(Cl)(H)(PPh3)3] with cycloheptatriene, cyclohepta-1,3-diene, cyclooctatetraene, penta-1,4-diene, cycloocta-1,5-diene and dimethyl maleate has been carried out spectroscopically. The major mechanism was found to involve dissociation of triphenylphosphine, followed by reaction with the organic ligand, although a second mechanism involving direct combination of the two reactants was also observed. 

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