Novel Cyclooctatetraene Radical Cation Planarized by Full Annelation with Bicyclo[2.1.1]hexene Units

Nishinaga, Tohru; Uto, Takayuki; Komatsu, Kôichi

doi:10.1021/ol047930y

Cited by 18 publications

(7 citation statements)

References 14 publications

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“…Thus, the relatively larger HOMO-LUMO gap (3.04 eV at the B3LYP/6-31G* level) for a planar COT, in which the LUMO level is raised by the orbital interaction with the annelated bicyclic ring (Figure 10), is considered to be the main reason for the reduced antiaromaticity in 14. Planar COT 14 has an unusually low oxidation potential (+0.07 V vs Fc/Fc + ) and gives a fairly stable radical-cation salt [82]. This is ascribed to the raised HOMO level due to the σ-π conjugative effects of bicyclic frameworks in addition to a narrowed HOMO-LUMO gap by the planarization of COT ring as shown in Figure 10.…”

Section: Planar Cot Annelated With Plural Bicyclo[211]hexene Ringsmentioning

confidence: 96%

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

2010

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Cyclooctatetraene (COT), the first 4nπ-electron system to be studied, adopts an inherently nonplanar tub-shaped geometry of D 2d symmetry with alternating single and double bonds, and hence behaves as a nonaromatic polyene rather than an antiaromatic compound. Recently, however, considerable 8π-antiaromatic paratropicity has been shown to be generated in planar COT rings even with the bond alternated D 4h structure. In this review, we highlight recent theoretical and experimental studies on the antiaromaticity of hypothetical and actual planar COT. In addition, theoretically predicted triplet aromaticity and stacked aromaticity of planar COT are also briefly described.

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Section: Planar Cot Annelated With Plural Bicyclo[211]hexene Ringsmentioning

confidence: 96%

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

2010

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“…The enhanced reactivity of 2 is evident as no reaction took place with the parent COT with TCNE under the same conditions. In spite of the supposed congestion in the transition state, the cycloaddition reaction was quite facile owing to the unusually elevated HOMO level of 2 15. A similar reaction was also reported to proceed with the nearly planar cyclobuteno derivative 18 ,31 which may be better described as a peripheral 10π‐electron system…”

Section: Resultsmentioning

confidence: 89%

“…In contrast to 1 , COT 2 showed no reduction in the range 0–−2.2 V versus Fc/Fc + and an unusually low oxidation potential (+0.07 V versus Fc/Fc + ). This compound, accordingly, gave a fairly stable radical cation salt,15 which is ascribed to a raised HOMO level as a result of the σ–π conjugative effects of bicyclic frameworks in addition to a narrowed HOMO–LUMO gap by planarization. The substantial decrease in the HOMO–LUMO gap of the COT ring in 2 is evident from the longest absorption maximum (459 nm),6 remarkably red‐shifted relative to that of the tub‐shaped tetrakis(bicyclo[2.2.2]octeno)cyclooctatetraene ( 4 ; 282 nm) 16…”

Section: Introductionmentioning

confidence: 99%

Antiaromaticity and Reactivity of a Planar Cyclooctatetraene Fully Annelated with Bicyclo[2.1.1]hexane Units

Nishinaga

Uto

Inoue

et al. 2008

Chemistry A European J

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A detailed investigation has been made into the antiaromaticity and chemical reactivity of a planar cyclooctatetraene (COT) molecule fully annelated with bicyclo[2.1.1]hexane units 2. In spite of its planar 8pi-electronic structure, theoretical calculations have indicated that the antiaromaticity of COT 2 is considerably decreased in comparison with a planar COT 16 with D 4h symmetry. This behavior appears to be related to the wider HOMO-LUMO gap of 2 relative to 16, which is caused by the raised LUMO level as a result of the effective sigma-pi* orbital interaction between the strained bicyclic framework and the COT pi system. The two-electron reduction of 2 required the use of potassium mirror or a combination of lithium/corannulene in highly dried [D8]THF at -78 degrees C under vacuum. In contrast, the [4+2] cycloaddition of 2 with tetracyanoethylene (TCNE) proceeded quite smoothly owing to the high-lying HOMO. Reaction of 2 with meta-chloroperbenzoic acid gave all-trans tetraepoxide 23 in the same way as the corresponding benzene derivative 3. While the Simons-Smith-type cyclopropanation of benzene 3 gave tricyclopropanated derivative 21, the reaction of 2 only afforded isomers of dicyclopropanated derivatives 25 and 26. Yet, the reactivity of 2 is higher than the parent COT, which does not show any reactivity under the same conditions. On the basis of homodesmic reactions, it was concluded that release of strain is also an important factor for such relatively high reactivity in the epoxidation and cyclopropanation of bicycloannelated COT 2 as well as benzene 3.

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“…As in this case, most radical cations of hydrocarbon molecules are unstable; however, the full annelation of bicycloalkenes to π-moieties was shown to be effective for stabilizing the radical cations by so-called "Bredt's rule protection". [35,36] Consequently, COT tetraannelated with bicyclo[2.1.1]hexene units [37] as well as bicyclo [2.2.2]octane units, [38] produced isolable COT radical cation salts. Among these, radical cation 1 * + has a planarized COT structure.…”

Section: One-electron Oxidationmentioning

confidence: 99%

Oxidation of a Dithieno[3,4‐b:3′,4′‐d]thiophene Cyclic Dimer Containing a Planar Cyclooctatetraene Ring: Retention of High Antiaromaticity During Reactions

et al. 2019

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One‐electron and peracid oxidations of dithieno[3,4‐b : 3’,4’‐d]thiophene cyclic dimer, which contains an antiaromatic planar cyclooctatetraene (COT) core, were conducted. The reaction of the cyclic dimer with SbCl5 produced isolable radical cation salts. Density functional theory (DFT) calculations showed that the spin density of the radical cation resides not on the COT ring but on the peripheral sulfur and carbon atoms in the thiophene unit with retention of high antiaromaticity based on the nucleus‐independent chemical shift (NICS). The peracid oxidation of the cyclic dimer was found to proceed not on the COT ring but on the bridging sulfur atom in the dithienothiophene moiety. The retention of the high antiaromaticity of the COT ring after the sulfoxide formation was experimentally confirmed based on the relative hardness, and also was theoretically supported by NICS calculations. Interestingly, the DFT calculations suggested that the high antiaromaticity does not enhance the reactivity towards the epoxidation on the COT ring.

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Novel Cyclooctatetraene Radical Cation Planarized by Full Annelation with Bicyclo[2.1.1]hexene Units

Cited by 18 publications

References 14 publications

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Antiaromaticity and Reactivity of a Planar Cyclooctatetraene Fully Annelated with Bicyclo[2.1.1]hexane Units

Oxidation of a Dithieno[3,4‐b:3′,4′‐d]thiophene Cyclic Dimer Containing a Planar Cyclooctatetraene Ring: Retention of High Antiaromaticity During Reactions

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