Convergent Enantioselective Synthesis of Vinigrol, an Architecturally Novel Diterpenoid with Potent Platelet Aggregation Inhibitory and Antihypertensive Properties. 1. Application of Anionic Sigmatropy to Construction of the Octalin Substructure
作者:Leo A. Paquette、Ronan Guevel、Shuichi Sakamoto、In Ho Kim、Jason Crawford
DOI:10.1021/jo0301301
日期:2003.8.1
The coupling of building blocks 15 and 36e in the presence of MgBr(2).OEt(2) at 0 degrees C proceeds with an exo stereoselectivity (3.2:1) considerably more advantageous for the acquisition of carbinol 37e than in the absence of the additive (exo/endo = 1:5.7). The pivotal transformation that sets all of the relevant stereocenters of the cis-octalin 55 is the oxyanionic-accelerated [3,3]-sigmatropic
在0摄氏度存在MgBr(2).OEt(2)的情况下,构建基块15和36e的耦合以exo立体选择性(3.2:1)进行,比不使用碳氢化合物37e时更有利于获得甲醇37e。加性(exo / endo = 1:5.7)。设置顺式八氢萘55的所有相关立体中心的关键转换是37e的氧阴离子加速的[3,3]-σ重排。一个显着的特征是在结构上强制采用了船状过渡态,该态可用于以全顺式排列方式正确设置四个邻甲硫氨酸氢。由于最初通过埃文斯恶唑烷酮方案对映选择性地安装了异丙基取代基,因此55转化为碘砜62的方法可以通过X射线晶体学确认所有绝对立体化学赋值。没有观察到分子内阴离子环化62以产生三环骨架。这种反应性的缺乏归因于构象因素,该构象因素抑制了正确的S(N)2反应轨迹的实现。