1986 Fiscal Year Final Research Report Summary
Development and Application of the Ring-Expansion of Alicyclic Carbocations with Carbon Monoxide
| Project/Area Number |
60550606
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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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 University, Associate Professor, Faculty of Eng, 工学部, 助教授 (50026358)
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| Co-Investigator(Kenkyū-buntansha) |
OKAMOTO Kunio Kyoto University, Professor, Faclty of Eng., 工学部, 教授 (90025841)
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| Project Period (FY) |
1985 – 1986
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| Keywords | Carbon monoxide / Adamantyl cation / Ring-expansion / 3,4-homoadamantanediol / Bridgehead aldehyde / Benzoyl triflate / Keto cation / ソルボリシス |
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| Research Abstract |
1. The carbonylation of the 1-adamantyl cation with carbon monoxide in carbon tetrachloride at atmospheric pressure in the presence of trifluoromethanesulfonic acid (triflic acid) and adamantane affords 3-hydroxy-4-homoadamantyl 1-adamantanecarboxylate (1) in 70% yield under appropriate conditions. Among various 1-adamantyl cation precursors tested, 1-adamantyl triflate and mesylate have given the best, comparable results. This reaction proceeds via the addition of the 1-adamantanecarbonyl cation to 1-adamantanecarbaldehyde, a transient intermediate, followed by the Wagner-Meerwein rearrangement. The hydroxy ester 1 is easily converted into 3,4-homoadamantanediol which is a promising starting material for 3,4-bifunctional homoadamantane derivatives.
2. Acylation of bridgehead aldehydes with the 1-adamantanecarbonyl cation generated from the 1-adamantyl cation and carbon monoxide, or with benzoyl triflate, in the presence of triflic acid causes ring-expansion of the aldehydes by one carbon atom. Work-up of the reaction mixture with water affords a bridgehead alcohol containing the acyloxyl group on the vicinal carbon, which on saponificating gives a vicinal glycol in good overall yields. For example, bicyclo[2.2.1]heptane-1-carbaldehyde gives bicyclo[2.2.2]octane1,2-diol which is not easily accessible by the other methods.
3. The 1,2-diols described above are easily converted to 2-oxo-1-triflates. These triflates, when solvolyzed, generate <alpha> -keto cations in which the vacant p orbital of the cationic carbon is almost perpendicular to the carbonyl p-orbital, permitting evaluation of the purely inductive destabilization of the carbocation by the adjacent carbonyl group. By comparing the rates of solvolysis of these triflates with the reported rates of the substrates which generate conjugated <alpha> -keto cations, the conjugative stabilization of tertiary aliphatic carbocations by an adjacent carbonyl group has been estimated to be at most 1.4 - 2 kcal <mol^(-1)> .
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