18 自動合成ロボットを活用した(±)-Baccatin IIIの全合成(口頭発表の部)

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In organic synthesis, a plenty of human efforts is necessary to supply synthetic intermediates. The time and energy in simply repeating processes in syntheses can be reduced utilizing automated synthesis apparatus. It is expected that laboratory automation can realize highly efficient, reproducible and safe synthesis of organic compounds. We report here the total synthesis of (±)-baccatin III (2) utilizing automated synthesizers. Initially, the synthetic routes of the A-ring 15 and C-ring 19 from geraniol (11) were established. The all synthetic steps of the A and C-rings were successfully applied to the automated synthesizer by optimizing the reaction conditions adequate to the synthesizer. We also developed the Ti(III)-catalyzed radical cyclization of epoxy-alkene and it was found to be effective as the stoichiometric system previously reported. The synthetic route of the B-ring cyclization precursor 27 from A-ring 15 and C-ring 19 was established. All reactions were accomplished utilizing a high performance solution phase automated synthesizer that we had recently developed. The crucial 8-membered ring formation was effectively assisted by micro-wave irradiation. It was found that the intramolecular alkylation of 27 was accelerated in the presence of excess amount of LiN(TMS)_2. The reaction period was dramatically decreased (10h→15min). Regio- and stereo-selective allylic oxidation and dihydroxylation of exo-alkene provided 30. Oxetane formation without deconjugation of Δ-11 to exo-alkene was crucial. Treatment of 31 with i-Pr_2NEt in HMPA provided the desired 32. After oxidation at 9, 13-positions of 32, we accomplished the total synthesis of (±)-baccatin III (2).
天然有機化合物討論会の論文
2005-09-15

18 自動合成ロボットを活用した(±)-Baccatin IIIの全合成(口頭発表の部)

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