2006 Fiscal Year Final Research Report Summary
Synthesis and Reaction of a Novel Conjugated Aromatic Azepinium Cation with 6 n Electron System
| Project/Area Number |
16550039
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Organic chemistry
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| Research Institution | Okayama University |
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Principal Investigator |
SATAKE Kyosuke Okayama University, Admission Center, Professor, アドミッションセンター, 教授 (50033387)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Heterocyclic Compounds / Azepines / Aromaticity / Azepinium ion / Azatropylium ion / Electrophilic Substitution / Delocalized Cation / ab initio Calculation |
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| Research Abstract |
In relation to the hydrocarbon analogue, cycloheptatriene (CHT), reaction pathways involving azepine compounds have been a long studied field of fundamental chemistry, although vastly limited to theoretical studies as experimental results have been rare. Among these pathways, of particular interest are those involving the aromatic azepinium cation and sigmatropic isomerization of the azepine ring. Recently attention has been drawn to the role of azepinium ions as intermediates in reactions of nitrenium with aryl compounds. For the first time, by dealkoxylation of 2H- azepines with titanium tetrachloride (TiCl_4) azepinium ions have been generated in solution and in the same account, were found to react electrophilically with water and amine in situ to give the corresponding 2-substituted 2H-azepines.
Investigation of the reactive properties of azepinium could lead to a deeper understanding of and provide further evidence for the character of this new family of aromatic cations. Reaction
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with harder nucleophiles has been confirmed, and reaction with softer nucleophiles, as in the Friedel Crafts reaction, could also generate valuable information on the electrophilic character of these delocalized cations. We recently reported the reaction via azepinium ion with various aromatic compounds, including benzene, where 2-phenyl-2H-azepine, and 3-phenyl-3H- azepine were formed. In order to attain a yet deeper and more fundamental view of the azepinium ion character, analysis of a less substituted cation free of bulky ring substituents must be conducted. Reaction of 2-isopropoxy-7-methoxy-2H-azepine with TiCl_4 in the presence of benzene gave a mixture of 2H-, 3H-and 4H-azepines. This reaction presumably occurs via the formation of 2-methoxyazepinium followed by electrophilic addition to benzene then deprotonation. The simplest form of azepinium so far, was synthesized and analysis of the electrophilic reactivity gave an elegant example of the character of the πLUMO, for which experiment and DFT prediction coincide. Less
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