2005 Fiscal Year Final Research Report Summary
Control of the Reactivity of Ketyl Radicals through Acid-Base Interaction with Proton and Metal Ions
| Project/Area Number |
15550028
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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 | Niigata University |
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Principal Investigator |
HASEGAWA Eietsu Niigata University, Institute of Science and Technology, Associate Professor, 自然科学系, 助教授 (60201711)
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| Project Period (FY) |
2003 – 2005
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| Keywords | Electron Transfer / Ketyl Radical / Proton / Metal Ion / Acid-Base Interaction |
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| Research Abstract |
We have investigated two major research subjects. One is related to photoinduced electron-transfer (PET) chemistry, and the other is related to samarium diiodide (SmI_2) chemistry. PET reactions of benzophenones with 1,3-dimethyl-2-pehnylbenzimidazoline (DMPBI) or 2-(2'-hydrohyphenyl)-1,3-dimethylbenzimidazoline (HPDMBI) were investigated, and then regioselective deprotonation of their radical cations were discovered. Namely, the radical cation of DMPBI donates a proton at C_2 position to the benzophenone ketyl radicals while the radical cation of o-HPDMBI donates a phenol proton. Electron-donating pyrenes were found to be more reliable sensitizers than the corresponding anthracenes in the PET reductions of certain carbonyl compounds cooperating with above and related benzimidazolines. Investigation of PET reaction of 2-halomethyl-2-(3-butenyl) substituted cyclic ketones with amine donors allowed us to propose that PET generated ketyl radicals do not undergo nucleophilic substitution b
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ut single electron transfer with distant carbon-halogen bonds in the same molecules. Reactions of SmI_2 with alkoxy carbonyl substituted ketones, acycloxy substituted ketones, or ketones possessing carbonate moieties were conducted to expand the versatility of SmI_2 promoted intramolecular ketone-ester coupling reactions, and the expected cyclic compounds were often obtained. Discovery of novel cyclization and ring-expansion reactions involving reductive formation and oxidative ring-opening of cyclopropanol derivatives was noteworthy. For example, cyclopropnaols derived from the reactions of certain γ-keto esters with SmI_2 were converted to benzotropolones by the treatment with appropriate oxidants. Also, oxidation reactions of cyclopropanol derivatives obtained from intramolecular samarium Barbier reactions of α-bromomethyl substituted cyclic ketones were studied. Notably, one-pot reactions of these sequential reduction and oxidation processes were successfully performed. Finally, regioselective ring-opening reactions of cyclopropyl silyl ethers depending on the electron transfer conditions employed were discovered. We will further conduct mechanistic investigations of above electron-transfer systems to achieve fine-control of the reaction pathways, and will try to exploit new types of electron-transfer based functional molecules and molecular systems. Less
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