P-22 連続的Michael反応を用いたPlukenetione Aの中心骨格合成と不斉合成の検討(ポスター発表の部)
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Plukenetione A is a natural product isolated from Clusia plukenetii. The structural feature is a highly oxygenated and densely substituted adamantane core. We have found a method for the construction of the poly-functionalized bicyclo [3.3.1]nonenes by successive Michael reactions of 2-cyclohexenones with methacrylates. We also found that the adamantanes could be constructed via successive Michael reactions, followed by a Dieckmann condensation when ethyl 2,4-dioxocyclohexanecarboxylate was used as a Michael donor. In this report, synthesis of the adamantnae core 1 of plukenetione A via the successive Michael reactions is described. The bicyclo[3.3.1]nonene 3 was obtained by the successive Michael reactions of cyclohexenone 5 with methacrylate 4. Introduction of the C10-gem-dimethyl group was carried out after the reduction of the C9-carbonyl group. The C4-carbonyl group was introduced by the allylic oxidation of 8. The C9-carbonyl group was restructured by the oxidation of 9. The C3-benzoylated product 2 was obtained from 11 via the vinyl anion. When 2 was treated with TfOH in CH_2Cl_2, the adamantane core 1 was obtained. In order to apply the developed strategy to the asymmetric construction of the adamantane core, the organocatalytic asymmetric Michael reactions of 12 and 15 with 13 were investigated. When the leaving groups with low leaving ability were used for 13, the stereoselectivity in the Michael reaction was enhanced. The reaction temperature also affected the stereoselectivity. Attempts to improve the reaction yield are now in progress.
- 天然有機化合物討論会の論文
- 2008-09-01
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