1991 Fiscal Year Final Research Report Summary
Development of Novel Synthetic Methods by Utilizing Carbocations and Its Application to Mechanistic Studies
| Project/Area Number |
02453092
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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 |
Synthetic chemistry
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| Research Institution | Kyoto University |
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Principal Investigator |
TAKEUCHI Ken'ichi Kyoto Univ., Hydrocarbon Chemistry, Professor, 工学部, 教授 (50026358)
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| Co-Investigator(Kenkyū-buntansha) |
KITAGAWA Toshikazu Kyoto Univ., Hydrocarbon Chemistry, Instructor, 工学部, 助手 (20183791)
KINOSHITA Tomomi Kyoto Univ., Hydrocarbon Chemistry, Instructor, 工学部, 助手 (10026289)
KOMATSU Koichi Kyoto Univ., Hydrocarbon Chemistry, Associate Professor, 工学部, 助教授 (70026243)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Ring-expansion / Homoadamantanone / Adamantanone / F-Struain / Solvolysis / Carbocation / Oxocation / Through-bond Interaction |
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| Research Abstract |
1. Development of New Synthetic Methods for Cage Compounds. 4-Homoadamantanones containing an alkyl or aryl substituent, or deuterium or carbon-13 on the 3-position were synthesized by utilizing our acylative ringexpansion techniqued Meanwhile, a convenient method for the synthesis of 4 (e)-hydroxy- or -methoxy-2-adamantanone was developed by utilizing the solvolysis of easily available 2-oxo-4 (a)-adamantly triflate.
2. Development of New System Showing Enhanced Ionization Due to F-Strain. Rigid cage compounds such as (Z)-2-ethylidenebicyclo[2.2.2]oct-l-yl triflate and (Z)-2-ethylidene-l-adamantyl mesylate and halides were found to solvolyze 200-10, 000 times faster than the corresponding E isomers. Molecular mechanics calculations showed that the origin of the enhanced rates is the repulsions between the (Z)-methyl group and the atom in the leaving group that is directly attached to the reaction center.
3. Structure of 2-Oxo Cations. The rates of solvolysis of various new 2methylene and 2-oxo bridgehead compounds were determined. The rate data showed that the intermediate carbocation from flexible 2-methylene compounds are stabilized by allylic conjugation, whereas that from the corresponding 2-oxo compounds cannot be stabilized by carbonyl conjugation. The results indicate the unimportance of carbonyl conjugation in carbocations.
4. Through-bond Interaction in 3-Oxo Cations. Previously, we proposed that the rates of solvolysis can be enhanced by the stabilization of the intermediate carbocation due to the through-bond interaction of the carbonyl lone-pair with the cationic p orbital. In the present work, 4-oxo-2 (e) adamantly triflate was found to solvolyze assisted by the through-bond interaction. On the other hand, the effect vanished in the solvolysis of 2-aryl-4-oxo-2 (e)-adamantly trifluoroacetate, which gives a highly stable carbocation. The results reinforce the previous. conclusion for the existence of the carbonyl through-bond interaction in carbocations.
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