A Formal Total Synthesis of Eleutherobin Using the Ring-Closing Metathesis (RCM) Reaction of a Densely Functionalized Diene as the Key Step: Investigation of the Unusual Kinetically Controlled RCM Stereochemistry
作者:Damiano Castoldi、Lorenzo Caggiano、Laura Panigada、Ofer Sharon、Anna M. Costa、Cesare Gennari
DOI:10.1002/chem.200500749
日期:2006.1
functionalized, dienes, which have all undergone cyclization to give the Z stereoisomers exclusively. A detailed investigation of this unusual cyclization stereochemistry by computational methods has shown that the E isomer of the ten-membered carbocycle is indeed less thermodynamically stable than the corresponding Z isomer. In fact, the selectivity is believed to be due to the dense functionality around the ruthenacyclobutane
不对称的氧化烯化反应和闭环复分解反应已用于合成化合物3,这是Danishefsky及其同事报道的在全合成eleutherobin中使用的关键高级中间体。通过两个立体选择性钛介导的Hafner-Duthaler氧化烯化反应,可以很容易地由六步制得的商业上可得的R-(-)-香芹酮按30克的总收率将醛6转化为二烯5。该反应以单一非对映异构体的形式高收率(分别为73%和83%)提供了所需的产物(分别为73%和83%),而烯丙醇已被保护为对甲氧基苯基(PMP)醚,先前的研究表明该化合物实际上有助于环与其他保护基团和相应的游离醇相比,封闭复分解反应。在强迫条件下,使用Grubbs的第二代催化剂13进行环化反应,以64%的收率得到了十元碳环(E)-14。该结果与相似但功能化程度较低的二烯形成鲜明对比,二烯均经过环化作用,仅得到Z立体异构体。通过计算方法对该异常环化立体化学的详细研究表明,十元碳环的E异构