22 マジンドリンAの全合成(口頭発表の部)

概要

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Total synthesis of madindoline A was achieved. Stereoselective construction of quaternary carbon was realized by alkylation of enolate derived from α,β-unsaturated imide possessing chiral auxiliary. The γ-proton of the α,β-unsaturated imide 9 was abstracted with NaHMDS to give enolate 12 stereoselectively which facilitated alkylation at α-position from bottom side to afford β,γ-unsaturated imide 10 in high stereoselectivity (Table 1, Scheme 2). This method was applied to the cyclopentenedione moiety of madindoline A (Scheme 3). The α,β-unsaturated imide 14 was alkylated to obtain imide 15 in 61% yield with 8.4:1 ds. Imide 15 was converted into ethylketone 17 which was oxidized to give triketone 19. Treatment of triketone with DBU in benzene at room temperature facilitated regioselective cyclization to afford cyclopentenedione 20 in high yield. This procedure was applied to the total synthesis of madindoline A. In the reductive amination step for the coupling of sterically hindered aldehyde 16 and acid-sensitive amine 23, we found that Sn(OTf)_2-NaBH(OAc)_3 method was effective. After the reductive coupling, side chain was transformed to triketone 28 which was subjected to regioselective intramolecular condensation to construct a madindoline skeleton. Removal of TBS group from 29 with TBAF completed the total synthesis of madindoline A.
天然有機化合物討論会の論文
2000-10-01