1992 Fiscal Year Final Research Report Summary
Mechanistic Investigation of Photosensitized Enantiodifferentiating Reactions
| Project/Area Number |
03453031
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
有機化学一般
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| Research Institution | Himeji Institute of Technology |
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Principal Investigator |
TAI Akira Himeji, Inst. of Tech., Faculty of Science, Professor, 理学部, 教授 (20029961)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Yoshihisa Himeji Inst. of Tech., Faculty of Science, Assoc. Prof., 理部学, 助教授 (30112543)
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| Project Period (FY) |
1991 – 1992
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| Keywords | Photochemistry / Asymmetric multiplication / Singlet Photosensitization / Photoisomerization / Aromatic ester |
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| Research Abstract |
In spite of the tremendous efforts devoted to the photosensitized enantiodifferentiating reaction for more than 25 years ever since the first attempt of this sort by Hammond and Cole, no efficient photochemical chirality transfer and multiplication have been materialized when we started the present study. In the present work, we employed the singlet sensitization with chiral aromatic ester as a facile method that assures longer and more intimate interaction between chiral sensitizer and prochiral substrate in the intervening diastereomeric singlet exciplex. Employing this strategy, we obtained extraordinary high optical yields up to 70% in the singlet sensitized photoisomerization of cycloalkenes. Unexpectedly it was shown that the direction of the product's optical rotation is inverted at the equipodal temperature.
The temperature dependence study of the product's optical yield indicated that the temperature switching of product chirality originates from the non-zero differential entropy of activation (DELTADELTAS<@D1(] SY.++.[)@>D1<@D2S-R@>D2). Historically, the entropy term has long been neglected or assumed to be very close to zero in the thermal and photochemical asymmetric reactions. Hence, the present result presents a new concept and a practical strategy for better optical yields in the global area of asymmetric synthesis.
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