Reaction with cyclooctatetraene

Cyclooctatetraene itself does not undergo 4 + 2 cycloadditions it is its valence isomer bicyclo[4.2.0]octatriene which reacts with dienophiles.36 Use Dewar s PMO method to explain why the direct reaction with cyclooctatetraene is disfavored. 

Reaction with cyclooctatetraene.6 With most dienophiles, cyclooctatetraene (I) reacts through the quasiplanar diene system of the valence tautomer bicyclo[4.2.0]-octatriene (2). For example, tetracyanoethylene reacts in this way to give (3). However,... 

Cycloadditions of 3,6-bis(trifluoromethyl)-l,2,4,5-tetrazine 147 to benzocyclopropene 177 <1996ZNB348>, bicy-clo[2.1.1]hex-2-ene 178 <2003EJ0901>, and secododecahedradiene dicarboxylate 179 <2001HCA1518> gave polycyclic pyridazine derivatives 181-183. Reaction with cyclooctatetraene 180 in refluxing dichloromethane afforded 1 1 and 1 2 cycloadducts 184 and 185 (Scheme 49) <1995LA661>. 

Reaction of Ru3(CO)i2 with cyclooctene affords Ru6(/i6-C)(/r3- 7 7 7 -C8Hi2)(CO)is 205 in 27% yield, resulting from dehydrogenation of the reagent. In contrast, reaction with cyclooctatetraene results in cluster degradation to give a binuclear complex, Ru2(/i-7]" 7" -C8H8)(CO)s. ... 

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). 

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

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

Dick turned up some interesting chemistry of caprolactam and its O-alkyl imino ethers. He and collaborators went on to explore the chemistry of allene, for example, its reactions with acetylene, carbon monoxide, and tetrafluo-roethylene. He did extensive work on the chemistry of cyclooctatetraene and of ferrocene. In the cyanocarbon area he collaborated on studies of the anion radical of tetracyanoethylene, that is, tetracyanoethylene bearing an extra electron. He was author or coauthor of 45 papers and 16 U.S. Patents that came out of the Central Research Department. 

Hisano and coworkers298 prepared tricycle 476 by reaction of cyclopentadienone 475 with cyclooctatetraene (474) in refluxing benzene (equation 141). Cyclized [4 + 2] cycloadduct 477 was isolated as a by-product. 

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). 

Several lanthanide cyclooctatetraene complexes have been synthesized, including both the divalent metal complexes Eu(CgHg) and Yb(CgH8) 44), and the trivalent complexes [M(CgH8)2] (M =Ce, Pr, Nd, SmorTb) 35). The former were preprired by direct reaction of the metal with cyclooctatetraene in liquid ammonia. No structural data exist for these divalent compounds, but they probably involve some kind of bridging interaction since, even with coordinated solvent, one COT... 

The synthesis of bis(rj8-cyclooctatetraene)uranium(IV) (uranocene)J from uranium tetrachloride and (cyclooctatetraene)dipotassium was first published in 1968.1 The method reported here is a modification of that procedure and is suitable for a large variety of cyclooctatefraene complexes.2-4 BisO 8-cyclo-octatetraene)uranium(IV) has also been prepared by the reaction of uranium tetrafluoride with (cyclooctatetraene)magnesium in the absence of solvent.5 Direct reaction of finely divided uranium metal with cyclooctatetraene vapors at 150° also gives some uranocene.5 However, both methods give low yields. 

The reaction of arc generated atoms with cyclooctatetraene (37) produces indene (22) in which the label is on C9. An initial DBA followed by ring opening to cyclononapentaene (38) is proposed. In analogy with known reactions of 38, electrocychc closure followed by H migration leads to 22- C9 (Eq. 25). 

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... 

Tetrahaptocyclohexatriene- and cyclooctatetraene-metal-tricarbonyl complexes undergo some unusual cyclo-addition reactions with tetracy-anoethylene in which the dienophile undergoes a 1,3 addition across the coordinated ligand and causes a rearrangement of the metal-carbon bonds, for example (99),... 

Two syntheses of Rh4(CO)i2 at ordinary pressure have been developed 81, 279 making this compound easily available, and CO scrambling in this molecule has been carefully examined 110,112,164. Strong nucleophiles including CO at high pressure destroy the Rh cluster 45, 396, but with phosphines of limited donor strength, with cyclooctatetraene, and with acetylenes up to four CO groups could be replaced with retention of the Rh4 unit 45, 247, 396. Rh4-like Rhg-clusters show catalytic activity (7 04, 364 which has been used for hydroformylation 88 and oxidation (297) reactions. 

Cyanogen azide reacts with cyclooctatetraene (112) at room temperature in ethyl acetate to give alkylidenecyanamide.326 At 78°, a 31% yield of a mixture of the alkylidenecyanamide (113) (68%) and the 1,4-adduct 114 (32%) is obtained. Since cyanogen azide decomposes above 40° and since the alkylidenecyanamide does not rearrange to the 1,4 adduct under the reaction conditions, one may believe that the 1,4 adduct forms directly from cyanonitrene and cyclooctatetraene. This is a case of 1,4 addition studied by Anastassiou.328... 

Interestingly, treating (>/4-cyclooctatetraene)Fe(CO)3 with acetyl chloride under Friedel-Crafts reaction conditions yielded unexpectedly222-223 the (>/2,>/3-8-e.x0-acetyl bicy-clo[3.2.1]octadienylium)Fe(CO)3 cation complex, presumably by rearrangement of the intermediate bicyclo[5.1.0]octadienylium isomer (Scheme 8). The structure of the rearranged cation was confirmed from the X-ray crystal structure and from the typical 1,3-cr.ji-allylic products obtained upon nucleophilic reaction with LiAlD4 and NaCN. The nucleophilic reaction of the more bulky iodide occurs, however, on the metal. 

Exercise 22-41 Write reasonable mechanisms for the different oxidation reactions of cyclooctatetraene with mercuric ethanoate in ethanoic acid, methanol, and water solutions. Notice that compounds of the type Hg(OR)2 appear to act in some cases as OR-donating agents and also that the oxide produced from cyclooctatetraene and peroxyacids (Section 15-11C) rearranges readily in the presence of acids to phenylethanal. 

Fe(cyclooctatetraene)(CO)3] reacts with TCNE to form a cycloadduct having the bicyclic structure (33) shown in equation (13).44-47 Addition is exo to the metal. Similar reactions with other electrophilic alkenes such as l,l-dicyano-2,2-bis(trifluoromethyl)ethylene have lso been observed.46... 

The reactivity of the incarcerated cyclobutadiene was probed by warming the NMR sample to 220°C for 5 min. This resulted in the formation of free cyclooctatetraene (6.108), clearly from ejection of the cyclobutadiene from the cavity and its subsequent dimerisation via 6.107. Reaction with 02 (which is able to enter the cavity of 6.101 gave incarcerated malealdehyde (6.109). 

In the cases of the olefin-bridged, iron complexes (OC)3Fe(olen)Fe(CO)3 (olen = cyclooctatetraene, l,l -di-2,4-cyclohexadienyl, 1, l -di-2,4-cyclo-heptadienyl), we have again shown that reaction with NaN(SiMes)2 leads exclusively to the corresponding monocyano complexes [(OC)[Pg.41]

Reactions of a metal carbonyl with an olefin. In the reaction of Mo(CO)6 with cyclooctatetraene, the olefin replaces two CO ligands ... 

Table 8. Relative amounts of 57 and 52 from reaction of NCN with cyclooctatetraene in various solvents 45>...

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