40 オブツセニン類の全合成(口頭発表の部)

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(+)-Obtusenyne 1, isolated from red alga (Laurencia obtusa) by Imre et al., has some isomers from another alga as well as sea here, such as (-)-12-epi-obtusenynes 2 from sea hare (Aplysia dactylomela) by Schmitz et al. and (-)-12?,13-epi-obtusenynes 3 from red alga (Laurencia pinnatifida) by Norte et al. Their common structures involve 9-membered ether rings having halogen functional groups and alkyl side chains as geometric isomers of enynes with various stereochemistries. The absolute stereochemistries of 1 and 2 have been determined by X-ray crystallographical analyses and various chemical methods, while that including C(12) on 3 has not been defined yet. We planned to synthesize 1 and determine the stereochemistry of 3 synthetically. The direct bromination to cyclic enol ether 10 with NBS in MeOH afforded a bromo acetal 23 which was reduced to bromo ether 24 with Et_3SiH and SnCl_4. The alcohols 27 and 28, which were obtained by epoxidation of 10 with dimethyldioxirane followed by reduction with DIBAH, were stereoselectively converted to 29 and 30 with CBr_4 and Oct_3P, respectively. The (Z)- and (E)-enynes were constructed stereoselectively with Sonogashira coupling via (Z)-monobromo and (E)-monoiodo olefin, respectively, obtained by Uenishi and Takai reactions. The first total syntheses of (+)-obtusenyne, (-)-12,13-epi-obtusenynes 4, and (+)-13-epi-obtusenynes 5 were thus achieved. Furthermore, the absolute configuration of C(12) on 3 was clarified as S including its absolute whole structure.
天然有機化合物討論会の論文
1998-08-31

40 オブツセニン類の全合成(口頭発表の部)

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