P-6 水銀トリフラートを活用した(±)-タルーシンの全合成と触媒オレフィン環化反応の開発(ポスター発表の部)

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Produced by marine bacterium, thallusin is an algal morphogenesis inducer that is indispensable for the foliaceous morphology of macroalgae. Thallusin, which was isolated in 2005 after chasing for more than 50 years, showed foliaceous morphology-inducing activity at the exceptionally low concentration of 1ag/mL at the first stage. The structure 1 was established via a spectral study as well as via the single crystal X-ray diffraction study of a thallusin derivative. In 2006, Snider and co-workers achieved the total synthesis of compound 1 from sclareol oxide 2. Because compound 1 did not show the foliaceous morphogenesis-inducing activity, the absolute structure of thallusin was determined to be the antipodal 3. Thallusin can be obtained in very limited amounts from cultivation. Thus, in the present study, the total synthesis of (±)-thallusin and analogues were undertaken to allow a detailed examination of thallusin's biological activity. The key steps of the synthesis is a Hg(OTf)_2・PhNMe_2-induced olefin cyclization of homofarnesyl acetate 6 leading to a bicyclic compound 7, and Suzuki coupling of enol triflate 25 with a pyridylboronic acid derivative 26. Hg(OTf)_2 also acted as a catalyst to isomerize the double bond into the more thermodynamically stable isomer when treated in toluene. Synthetic (±)-thallusin as well as an analogue showed morphogenesis activity. On the other hand, we have developed a variety of Hg(OTf)_2-catalyzed reactions base upon the significant π-philicity of this reagent. For example, the reaction of arylalkyne 33 with 0.1mol % of Hg(OTf)_2・3TMU affords 34 in 99% yield. Protonation of vinyl mercuric intermediate 35 with in situ formed TfOH leading to cation 36 is the key step of the catalytic syntem. Now we introduce oxygen functionality nearby as the protonation site and succeeded the Hg(OTf)_2-catalyzed olefin cyclization. Reaction of 37 with 0.2mol % of Hg(OTf)_2 afforded 38 in 90% yield, and the reaction of Hg(OTf)_2 with 1mol % of Hg(OTf)_2 afforded 42 in 84% yield.
2007-08-24

P-6 水銀トリフラートを活用した(±)-タルーシンの全合成と触媒オレフィン環化反応の開発(ポスター発表の部)

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