| Project/Area Number |
10640508
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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 | TOHOKU UNIVERSITY |
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Principal Investigator |
KOSUGI Hiroshi Institute for Chemical Reaction Science, Tohoku University, Associate Professor, 反応化学研究所, 助教授 (80006329)
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| Project Period (FY) |
1998 – 1999
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| Project Status |
Completed (Fiscal Year 1999)
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| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1999: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1998: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Keywords | asymmetric synthesis / chiral sulfur compound / asymmetric protonation / asymmetric polyene cyclization / triptoquinone / 不斉アルキル化反応 |
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| Research Abstract |
The aim of this research project is to develop the synthetic utilities of chiral sulfur compounds in asymmetric synthesis. Especially we focused on the following two main problems :
(1) Mechanistic aspects of enantiofacial protonation of prochiral Li enolates with chiral β-hydroxy sulfoxides and its synthetic application.
(2) Asymmetric polyene cyclization of chiral β-hydroxy sulfides via an episulfonium ion.
Through our efforts to solve these problems, we obtained the following intriguing results.
(1) (2S,RィイD2SィエD2)-3,3,3-Trifluoro-1-[(4-methylphenyl)sulfinyl]propan-2-ol (1a) is the most powerful chiral protonating reagent for the prochiral lithium enolates. While the protonation of the enolates of the alkyl substituted cyclohexanone derivatives with 1a affords S-products, the protonation of the enolates having a 4,4-dioxygen functionality with 1a resulted in the reverse selectivity. For the present protonation the presence of extra LiBr is essential to attain the high level of enantioselectivity. Furthermore we obtained the present methodology can be extended to the asymmetric alkylation of prochiral enolates of β-keto esters.
(2) We developed the new type of asymmetric polyene cyclization employing chiral β-acetoxy sulfides as the initiating moiety. The present cyclization proceeds via an episulfonium ion to afford the optically pure bicyclic or tricyclic compounds. We could apply the present method to synthesize the enantiomerically pure natural products, triptoquinones which was isolated from Tripterygium wilfordii.
We also found that the mono-substituted β-acetoxy sulfides undergo cyclization to afford the corresponding tricyclic compounds. Accordingly, we could show the present method is superior to the conventional polyene cyclization using an epoxide as an initiating group.
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