Cyclooctatetraene oxide

The existence of a metalated epoxide was first proposed by Cope and Tiffany, to explain the rearrangement of cyclooctatetraene oxide (8) to cydoocta-l,3,5-trien-7-one (11) on treatment with lithium diethylamide. They suggested that lithiated epoxide 9 rearranged to enolate 10, which gave ketone 11 on protic workup (Scheme 5.4) [4],... 

The valence isomerization of cyclooctatetraene oxide to all-cis-oxacyclononatetra-ene is of interest both theoretically and practically. ... 

Cope and Tiffany found this amide a superior reagent for the isomerization of cyclooctatetraene oxide (1) to l,3,5-cyclooctafriene-7-one (3). They postulate that... 

A two-step ring contraction of cyclooctatetraene oxide (14) has been effected with Ag(I) (equation VI). 

Although they are sometimes utihsed for their nucleophihc properties, as out-hned above hthiated epoxides are carbenoid species, and they are well known to react through C-H and C=C insertion or 1,2-shift processes. Following his early studies on cyclooctatetraene oxide. Cope extended his work to stilbene derivatives 58 and 60 (Scheme 10) [47]. The ketone 59 and aldehyde 61 were derived from (formal) 1,2-shift of the group (either H or phenyl, respectively) cis to hth-ium on the lithiated epoxide. 

The intermediacy of an a-lithiated oxirane was postulated for the first time by Cope in the 1950s while studying the reaction of cyclooctatetraene oxide with hthium diethylamide (1951JA4158, 1960JA6370). Since then, and particularly over the last 10 years, many synthetic methodologies have... 

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). 

Three decades ago the preparation of oxepin represented a considerable synthetic challenge. The theoretical impetus for these efforts was the consideration that oxepin can be regarded as an analog of cyclooctatetraene in the same sense that furan is an analog of benzene. The possibility of such an electronic relationship was supported by molecular orbital calculations suggesting that oxepin might possess a certain amount of aromatic character, despite the fact that it appears to violate the [4n + 2] requirement for aromaticity. By analogy with the closely related cycloheptatriene/norcaradiene system, it was also postulated that oxepin represents a valence tautomer of benzene oxide. Other isomers of oxepin are 7-oxanorbornadiene and 3-oxaquadricyclane.1 Both have been shown to isomerize to oxepin and benzene oxide, respectively (see Section 1.1.2.1.). 

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). 

See other induction period incidents See Potassium - Slow oxidation See Dipotassium // cyclooctatetraene... 

Uranium complexes analogous to these compounds were also described, but with the cot (cyclooctatetraene dianion) ligand rather than the Cp or Cp ones. Both the dianionic U(IV) [(cot)U(dddt)2]2 [47] and monoanionic U(V) [(cot)U(dddt)2] [48] complexes were isolated and structurally characterized (Fig. 5). Spectacular distortions of the US2C2 metallacycles were rationalized on the basis of DFT calculations, which reproduced the spectacular folding of the endo US2C2 metalla-cycle when the dianionic species undergoes an oxidation. 

The behavior of the same azoxybenzene is studied in homogeneous conditions— when the dipotassium salt of cyclooctatetraene dianion (CgHgKj) acts as a dissolved electrode. In this case, the reduction of azoxybenzene stops at the very first stage, that is, after the transfer of one electron only (Todres et al. 1975). The initial one-electron reduction produces the azoxybenzene anion-radicals, which are not reduced further despite the presence of residual electron donor in the solution. The ESR method does not reveal these anion-radicals although one-electron oxidation by phenoxyl radicals quantitatively regenerates azoxybenzene and produces the corresponding potassium phenolate molecules in a quantitative yield. Treatment with water leads to a 100% yield of azobenzene (Scheme 2.14). 

Eight-membered heterocyclic systems embrace a very broad variety of compounds ranging from cyclic ethers and imines to highly labile analogs of cyclooctatetraene, and the properties and chemical behavior of these compounds of course depend entirely on the extent and location of unsaturation. For this reason, preparative methods and reactions are treated together for each ring system and oxidation level. 

Recently, in a study of a large number of organo-iron compounds 120), it has been found possible to treat the isomer shift as being due to a sum of partial isomer shifts 8,. from individual ligands which for 7r-cyclopentadienyl derivatives could be correlated with proton NMR chemical shifts in the same compounds. The Mossbauer spectra of two cases of theoretical interest are worthy of mention. First, the spectra of both the mono- and binuclear iron tricarbonyl derivatives of cyclooctatetraene 115) show similar 8 and A values. The small 8 values are consistent with zero oxidation state for the iron atom and essentially complete covalent bonding between the iron and the tt electrons of the ring, so that, at least for the mononuclear... 

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. 

The 18 n-electron system furo[3,4-c]octalene (356) is available by a Wittig reaction starting from cyclooctatetraene-1,2-dicarboxaldehyde it is obtained as an unstable pale yellow liquid, which is rapidly oxidized in air. The electronic spectrum resembles that of 353, showing little extended conjugation. Compound 356 underwent Diels-Alder addition at the terminal cyclooctatetraene ring thus treatment with dimethyl fumarate leads to monoadduct 357. ... 

By use of a similar method other more stable 1-substituted phosphiranes are prepared, 1-phenylphosphirane (123) being the most stable. When the cyclooctatetraene dianion is treated with dichlorophenylphosphine the bicyclic 1-phenylphosphirane derivative (124) is formed. At 70 °C in CHC13 it rearranges into the bicyclic phosphabicyclo[4.2.1]heptane derivative (125). Oxidation and photochemical reaction give the tricyclic phospholene 1-oxide derivative (126 equation (76)) (66JA3832). 

The diverse ways in which cyclooctatetraene can react with a given reagent under different conditions is well illustrated by the variety of products obtained on oxidation with mercuric ethanoate in ethanoic acid, methanol, and water ... 

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