Total synthesis of (–)-C<sub>34</sub>-botryococcene, the principal triterpenoid hydrocarbon of the freshwater alga Botryococcus braunii
作者:James D. White、G. Nagabushana Reddy、Gary O. Spessard
DOI:10.1039/p19930000759
日期:——
C-13. The pair of stereoisomeric hydroxy esters 24 and 25 obtained from this rearrangement were independently advanced to stereochemical convergence at 29, which was subsequently transformed into diiodide 37. The route of synthesis confirms the previous assignment of absolute configuration made to botryococcene 1 at five of the six stereogenic centres, i.e. (3S,7S,10R,16S,20S).
通过将烷基铜物质41偶联到二碘化物37的每个末端上,以对映体纯净的形式合成了碳氢化合物(-)-C 34- botocrococcene 1。前者由(2S)3-羟基-2-甲基丙酸酯2制备,其首先被转化为醇7。通过与Schlosser碱进行质子化而得到的二价阴离子7与甲苯磺酰基酯11偶合,得到醇12和碘化物39。中心段37的botryococcene链的从(2合成ř)-3-羟基-2-甲基丙酸酯15并引起衍生的αβ-不饱和MOM酯23发生新的重排,以在C-13处建立季烯丙基中心。从该重排获得的一对立体异构羟基酯24和25在29处独立地前进至立体化学会聚,随后转变为二碘化物37。合成路线确认绝对构型的以前的分配作出botryococcene 1五六个立体中心的,即。(3 S,7 S,10 R,16 S,20S)。