Antiaromaticity and Reactivity of a Planar Cyclooctatetraene Fully Annelated with Bicyclo[2.1.1]hexane Units
| Autor: | Akira Matsuura, Noach Treitel, Takayuki Uto, Koichi Komatsu, Ryota Inoue, Mordecai Rabinovitz, Tohru Nishinaga |
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| Rok vydání: | 2008 |
| Předmět: |
Models
Molecular Magnetic Resonance Spectroscopy Molecular Structure Bicyclic molecule Organic Chemistry General Chemistry Reference Standards Tetracyanoethylene Crystallography X-Ray Photochemistry Medicinal chemistry Catalysis Cycloaddition Bridged Bicyclo Compounds Cyclooctanes chemistry.chemical_compound Cyclooctatetraene Models Chemical chemistry Corannulene Quantum Theory Computer Simulation Reactivity (chemistry) HOMO/LUMO Antiaromaticity |
| Zdroj: | Chemistry - A European Journal. 14:2067-2074 |
| ISSN: | 1521-3765 0947-6539 |
| DOI: | 10.1002/chem.200701405 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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