Studies toward the Total Synthesis of Dumsin. 2. A Second Generation Approach Resulting in Enantioselective Construction of a Functionalized ABC Subunit of the Tetranortriterpenoid Insect Antifeedant
作者:Leo A. Paquette、Yang Hu、Andreas Luxenburger、Raynauld L. Bishop
DOI:10.1021/jo062068o
日期:2007.1.1
seco ketoacid. The same advanced intermediate was obtained by initially positioning the double bond internal to the five-membered ring in advance of transient ring expansion via diketone formation and intramolecular aldolization. Both of these approaches bypass the complications arising from the substantial steric congestion prevailing in these structural networks. The task of covalently positioning an
描述了dumsin的ABC框架的合成。光学活性中间体9b通过顺序执行oxy-Cope重排和分子内烯类反应从新戊酸5-氧冰片酯迅速组装而成,被证明可适当官能化以最终转化为5。合成计划依赖于针对这种目标中间体的两种方法。首先,在EtAlCl 2期间引入的环外双键促进了醛10b的封闭裂解以留下适合氢化物还原和除水的羰基。用四氧化钌裂解所得的双键提供了癸二酮酸。通过在通过二酮形成和分子内醛醇缩合进行的瞬态环膨胀之前首先将双键定位在五元环内部而获得相同的高级中间体。这两种方法都绕开了由这些结构网络中普遍存在的严重空间拥堵引起的并发症。将氧原子共价定位在5中与宝石-二甲基取代的碳相邻的任务通过氧化脱羧可以适当地实现。X射线晶体学分析[ 43]证实了许多中间体的立体化学归属。