15 タキサン類の合成研究(口頭発表の部)  [in Japanese] 15 SYNTHETIC STUDIES ON TAXANE DITERPENES  [in Japanese]

A highly efficient eight-membered ring cyclization enabled us to construct taxane carbon framework containing appropriate functionalities for synthesis of natural taxane families. Diketone 16 was prepared eventlessly in 5 steps from manisaldehydedimethylacetal 10. Regioselective silylation, followed by Peterson olefination, afforded cyclization precursor 24. TiCl_4 induced eight-membered ring cyclization occurred rapidly at law temperature to give 26 in 84% isolated yield. The overall yield from the starting material 10 was 33% (8 steps). Interestingly, no intermolecular coupling product was observed though the reaction was performed in 0.1M solution. It should be noted that the tricycle 26 was a single stereoisomer with the same stereochemistry with natural taxanes. We are currently pursuing a total synthesis of taxusin by applying this methodology.