Cyclooctatetraene reactions

Dehydrogenation cf. 4, 485). Causing and Wilke have reported two high-yield preparations of cyclooctatetraene. Reaction of 1,5-cyclooctadiene (1) and -butyllithium-TMEDA in a ratio of 1 3 gives the crystalline compound 2 in practically quantitative yield. Cyclooctatetraene (3) is obtained from 2 by oxidation with CdCl2. The intermediate 2 can also be obtained from 1,3,6-cycloocta-triene, but not from 1,3-cyclooctadiene or 1,3,5-cyclooctatriene. 

Barrelene was obtained via a double Diels-Alder reaction from a-pyrone with methyl acrylate (H.E. Zimmerman, I969A). The primarily forming bicyclic lactone decarboxylates in the heat, and the resulting cyclohexadiene rapidly undergoes another Diels-Alder cyclization. Standard reactions have then been used to eliminate the methoxycarbonyl groups and to introduce C—C double bonds. Irradiation of barrelene produces semibullvalene and cyclooctatetraene (H.E. Zimmerman. 1969B). 

Dimethyl acetylenedicarboxylate (DMAD) (125) is a very special alkyne and undergoes interesting cyclotrimerization and co-cyclization reactions of its own using the poorly soluble polymeric palladacyclopentadiene complex (TCPC) 75 and its diazadiene stabilized complex 123 as precursors of Pd(0) catalysts, Cyclotrimerization of DMAD is catalyzed by 123[60], In addition to the hexa-substituted benzene 126, the cyclooctatetraene derivative 127 was obtained by the co-cyclization of trimethylsilylpropargyl alcohol with an excess of DMAD (125)[6l], Co-cyclization is possible with various alkenes. The naphthalene-tetracarboxylate 129 was obtained by the reaction of methoxyallene (128) with an excess of DMAD using the catalyst 123[62],... 

The first breakthrough came m 1911 when Richard Willstatter prepared cyclooc tatetraene by a lengthy degradation of pseudopelletienne a natural product obtained from the bark of the pomegranate tree Today cyclooctatetraene is prepared from acetylene m a reaction catalyzed by nickel cyanide... 

Nickel plays a role in the Reppe polymeriza tion of acetylene where nickel salts act as catalysts to form cyclooctatetraene (62) the reduction of nickel haUdes by sodium cyclopentadienide to form nickelocene [1271 -28-9] (63) the synthesis of cyclododecatrienenickel [39330-67-1] (64) and formation from elemental nickel powder and other reagents of nickel(0) complexes that serve as catalysts for oligomerization and hydrocyanation reactions (65). 

The addition of benzonitrile oxide to cyclooctatetraene produced a monoadduct which was induced to undergo valence tautomerism to produce a tricycloisoxazoline (Scheme 104). A similar reaction with tropone gave a minimum of eight adducts from which two monoadducts were isolated (Scheme 104) (70T5113). 

Problem 15.7 Cyclooctatetraene readily reacts with potassium metal to form the stable cycio-octatetraone dianion, C8H82. Why do you suppose this reaction occurs so easily What geometry do you expect for the cyclooctatetraene dianion ... 

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

Connelly et al. (1979) investigated the reactions of arenediazonium salts with cyclooctatetraene (cot) and some of its transition metal compounds. Free cyclooc-... 

Few 1 -benzothiophene-S-oxides 218 were obtained in moderate yields by treatment of 1-arylacetylenes 219 with sulfur dioxide and benzene in the presence of antimony pentafluoride250 (equation 127). A series of cyclic sulphoxides have been prepared by hydrolysis of the corresponding alkoxy sulphonium salts 220251-254 (equation 128). Syn-sulphoxide 221 was obtained in a low yield (15-20%) in the reaction of the dianion of cyclooctatetraene 222 with thionyl chloride255 (equation 129). 

For studies of the mechanism of the reaction that produces cyclooctatetraenes, see Diercks, R. Stamp, L. Kopf J. tom Dieck, H. Angew. Chem. Int Ed. Engl., 1984,... 

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 " ... 

Table 4.12 Summary of reaction metrics and synthesis tree parameters for cyclooctatetraene synthesis plans ranked according to overall kernel (maximum) RME .

A warning was given that the 5 molar solution in ether used as a solvent for Diels-Alder reactions would lead to explosions [1], Such a reaction of dimethyl acetylenedicarboxylate and cyclooctatetraene in this solvent exploded very violently on heating. The cyclooctatetraene was blamed, with no supporting evidence [2], It would appear desirable to find the detonability limits of the mixture with ether before any attempt is made to scale up. A safe alternative to lithium perchlorate/ether as a solvent for Diels-Alder reactions is proposed [3],... 

Cyclooctatetraene (COT) —> Semibullvalene (SB) Photorearrangement. Irradiation of COT yields semibullvalene [97], in spite of the fact that this photochemical reaction is forbidden by orbital conservation mles. The Longuet-Higgins loop for this system actually predicts that this should happen, although the reaction is phase preserving. (Fig. 42). This is another example of type C loop (Fig. 11). Only six of the eight electrons re-pair as COT transforms to SB. The reaction is made possible by the fact that COT valence isomerization, a phase-inverting reaction (four electron-pair Hiickel system), takes place simultaneously. One expects to produce in the reaction a COT isomer, that can be detected solely by proper substitution. 

The reaction of Mo(CO)s with cyclooctatetraene is an example of this type of reaction ... 

Synthetic applications of other decarbonylation reactions are found in the conversion of cyclooctatetraene to barrelene 250), with the photodecarbonyla-tion of a Diels-Alder adduct as key step (2.31) and the preparation of tetrathioesters from 1,3-dithioles (2.32) 251). The most remarcable application of such a reaction up to date is the synthesis of tetra t.butyltetrahedrane from a tricyclic ketone precursor (2.33) 252). 

Cyclooctatetraene and some of its derivatives are electrochemically reducible in dry degassed DMF containing BU4NCIO4 as the supporting electrolyte. The first reduction peak potentials which are required to form the corresponding anion radical are shown in Table 824, though a further reaction of the intermediates is not known. 

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. 

For cyclooctatetraene and its product, so the equilibrium strongly favours the former to such an extent that the half life of the bicycloisomer is only a few minutes at 0°C. Thus as the bicyclic system becomes very strained, the equilibrium lies more in favour of the reverse reaction. 

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