4 O,S-アセタールを基盤としたシガトキシン類統一的全合成(口頭発表の部)

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With their imposing molecular structure, the ladder-shaped polyethers pose considerable challenge to synthetic chemists. Because the linear construction of the ether rings is virtually impossible due to the large and complex structure, the development of an efficient methodology for coupling the fragments, which is suitable for use in the advanced stages of synthesis, has been particularly important for the total synthesis. In this presentation, we will report the new convergent total synthesis of 51-hydroxyCTX3C (2), which has one of the most complex structures among the natural polycyclic ethers. Recently, we have developed a direct method to form O,S-acetal 5 from a secondary alcohol 3 and a halosulfide 4. The O,S-acetal of 6, synthesized from 5, was used as radical donor to cyclize the seven-memberd ether ring of 7, which was further transformed to fused ether structure 8 through the C-C bond formation (method A). Alternatively, the enol ether of 9 that was prepared from 5 was utilized as a radical acceptor to form six-memberd ether ring 10, from which 8 was synthesized via the reductive etherification (method B). While the method B was successfully applied to the CD-ring region of 2, the method A enabled the construction of the central FG-ring system after the final coupling between the left (ABCDE) and right (HIJKLM) ring system. By using these free radical approaches, the first total synthesis of 51-hydroxyCTX3C (2) was accomplished in a concise and efficient fashion.
天然有機化合物討論会の論文
2005-09-15

4 O,S-アセタールを基盤としたシガトキシン類統一的全合成(口頭発表の部)

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