Cyclooctatetraene dimers

To date, attempts to prepare any of the tetramantane isomers have not been successful. In fact, one such attempt has provided the first example where thermodynamic control alone was not sufficient to give the desired product. Elaboration of the cyclooctatetraene dimer (18) to the desired C and H level followed by hydrogenation and rearrangement (Eq. 10)) gave 22 instead of one or more of the tetramantane isomers 351. 

Intramolecular cycloaddition also played a central role in the synthesis of Dewar benzene (145, equation 12.89), the bicycloheptenol 146 (equation 12.90), and the tricyclic keto ethers 147 and 148 (equation 12.91). The photochemical retro Diels-Alder reaction was also us for a synthesis of bullvalene (149) from cyclooctatetraene dimer (equation 12.92). ... 

Ci6HigAgN03, Cyclooctatetraene dimer-silver nitrate, 23, 640 ClgHigB2Fe204, Di-M carbonyl-dicarbonylbis(1-methylborinato)diiron, 40B, 790... 

C19H16O3RU, Tricarbonyl(cyclooctatetraene dimer)ruthenium, 45B, 1005 Cl9H22CI2N2RU, Dichlorobis(phenylamine)(bicyclo[2.2.1]hepta-2,5-di-ene)ruthenium, 40B, 794... 

Compound (XLI) does not undergo a Diels-Alder reaction with maleic anhydride but recently a 1 1 adduct with tetracyanoethylene has been obtained (30, 61). Schrauzer and Eichler (61) have found that two isomeric products, presumed to be Fe(CO)3 complexes of cyclooctatetraene dimers, are obtained when (XLI) is irradiated in the presence of cyclooctatetraene. As mentioned in Section III, A, 2, these isomers, upon irradiation with Fe(CO)5, eliminate benzene to form the same binuclear complex CioHtoFe2 (CO)g. The structures of these complexes have not been rigorously established. 

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). 

If the nitro group is located at the ethylene fragment, one-electron transfer initiates dimerization of the developing anion-radicals. a-Nitrostilbene, w-methyl-co-nitrostyrene, and a-nitro-p-ferrocenylethylene give anion-radicals, which dimerize spontaneously. It is interesting to compare reactions of cyclooctatetraene dipotassium (C8HgK2) with a-nitro and a-cyano ferrocenylethylenes (Todres and Tsvetkova 1987, Todres and Ermekov 1989 Scheme 3.4). 

Trace amounts of cyclic acetals are produced from the [2+2] dimer of cyclooctatetraene on ozonolysis in a 2 1 mixture of dichloromethane and methanol followed by stirring with Amberlyst 15 resin (Equation 39) <2003TL9313>. 

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... 

Of the cyclic olefins, norbornadiene replaces two CO groups from one Co to yield a labile complex 159, 160, 235), cyclooctatetraene replaces the axial CO ligands from all three cobalt atoms 53) and is itself replaced by other Lewis bases 330), and cyclopentadiene forms the unusual complex [95] with Co3(CO)gCMe 159,160). A few catalytic reactions were observed with methinyltricobalt enneacarbonyls including the dimerization of norbornadiene 160, 235) and the polymerization of functional olefins 312) with different Co3(CO)9CX. 

Formally, although these cyclooligomerizations can be considered as cycloaddition reactions, they are known not to occur through a direct cycloaddition process. In the best understood nickel-catalyzed reaction the dimer 12 was shown to be the key intermediate in cyclization.46,59 60 Acetylene readily undergoes cyclooligomerization in the presence of metal catalysts to form benzene and cyclooctatetraene [Eq. (13. 15)] as well as higher homologs ... 

The most intriguing hydrocarbon of this molecular formula is named bullvalene, which is found in the mixture of products of the reaction given above. G. Schroder (1963, 1964, 1967) synthesized it by a thermal dimerization presumably via diradicals of cyclooctatetraene and the photolytical cleavage of a benzene molecule from this dimer. The carbon-carbon bonds of bullvalene fluctuate extremely fast by thermal Cope rearrangements. 101/3 = 1,209,600 different combinations of the carbon atoms are possible. 

Anhydrides also undergo photodecomposition with loss of carbon dioxide.453 Tetrafluorocyclobutadiene (520) can be prepared in this way from the anhydride (521) and is isolated as the [ 4 + 2] adduct (522) with furan.454 In the absence of furan, the dimer (523) and the cyclooctatetraene (524) were obtained. Examples of photoelimination of carbon dioxide from cyclic carbonates have been described 455... 

The photodimerization of a silylalkynylbenzene to cyclooctatetraenes has been reported by West and coworkers194. It was proposed that this occurred via intermolecular [2 + 2] dimerization followed by ring opening to the cyclooctatetraene (equation 44). 

Triamantane (13) is obtained from the rearrangement of the heptacyclic dimer of cyclooctatetraene (18), after it has been elaborated to the C1S level by Simmons-Smith cyclopropanation and subsequent hydrogenolysis (Eq.(9))33l. The structure of the product, obtained in 5% yield, is again confirmed by an X-ray analysis 34>. 

The tail-to-tail dimerization of acrolein [3] and acrylonitrile [4, 5] was also obtained, with a lower reactivity and stereoselectivity. However, the dimerization of acrylonitrile was performed under mild conditions in the presence of molecular hydrogen with Ru(COD)(COT), where COT is cyclooctatetraene, [4] (Eq.2). 

The head-to-head dimerization with formation of a butatriene derivative was scarcely observed as the main catalytic route (Scheme 15, catalytic cycle B). Nevertheless, this was the case from benzylacetylene in the presence of RuH3Cp (PCy3) as a catalyst precursor in tetrahydrofuran at 80 °C, which gave more than 95% of (Z)-l,4-dibenzylbutatriene [54], and from ferf-butylacety-lene with two efficient catalytic systems capable of generating zero-valent ruthenium species, RuH2(PPh3)3(CO) and Ru(cod)(cyclooctatetraene) in the presence of an excess of triisopropylphosphine, which led to (Z)- 1,4-di- tert-butylbutatriene as the major compound [57-59]. 

In the presence of Ru(cyclooctadiene)(cyclooctatetraene)/6 PPh3, dimerization of HC=CSiMe3 leads to effective formation of l,4-bis(trimethylsilyl)butatriene (Eq.64) [108],... 

The [2+2] dimer 72 of cyclooctatetraene was subjected to ozonolysis and further stirring with Amberlyst 15 resin to furnish the tetraoxaperistylane 73 (see Section 14.09.2) and cyclic acetals 74-76 (Equation 23) <1999TL2417, 2003TL9313>. 

Alkynes can be selectively dimerized, cyclotrimerized, or polymerized with a large variety of transition metal and lanthanide catalysts nickel also catalyzes the cyclote-tramerization of HC=CH to cyclooctatetraene. Very electrophilic complexes such as Cp 2LnR and Group 4 compounds,137 as well as 18-electron species such as Cp RuH3(L) and Ru(Tp)Cl(PPh3)2, catalyze the linear dimerization of terminal alkynes 138... 

Cyclooctatetraene is also of some interest in metal atom chemistry. Codeposited with Ti, Fe or Co, are formed uncharacterized polymers ". With Cr a Cr Cr bonded dimer, Cr2(C8Hg)3, is formed (see below) ". With Ti, a novel triple decker sandwich is obtained. ... 

Tricyclo 4.4.2.0l 6]dodeca-3,11-dien E17f, 740 (2-C1 — tricycl.-thiolan — 5,5-dioxid/ROK) ejru-Tricyclo 6.2.2.02,7 dodeca-3,9-dien IV/5a, 296/E19c, 90 (1,3-Cyclohexadien-Dimer.) Tricyclo]6.4.0.02 7]dodeca-3,5-dien E17e, 241 [Cyclooctatetraen + Br—(CH2)4 — Br/LiNH2] Tricyclo 6.4.0.0I 7 dodeca-3,ll-dien IV/5a, 296... 

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