Synthesis of Cembranoid Analogues through Ring-Closing Metathesis of Terpenoid Precursors: A Challenge Regarding Ring-Size Selectivity
作者:Tanja Heidt、Angelika Baro、Andreas Köhn、Sabine Laschat
DOI:10.1002/chem.201502051
日期:2015.8.24
terpenoids were suitable precursors, despite the presence of competing double bonds in their framework. The size of R and R1 is crucial for successful macrocyclization. Whereas small alkyl substituents at the double bond directed the RCM towards six‐membered ring formation, cross metathesis leading to dimers dominated for bulkier alkyl groups. A similar result was obtained for precursors without functional
本文描述了使用Grubbs II催化剂对类天麻大环进行开环复分解的系统研究。由香叶醇衍生的三烯和基于溴代烯烃和丙二酸二甲酯的片段制备相对于RCM活性末端在同质位置上具有官能团X且直接连接至另一个末端双键的取代基R,R 1的无环萜烯。尽管它们的骨架中存在竞争性双键,但此类萜类化合物还是合适的前体。R和R 1的大小对于成功实现大环化至关重要。尽管双键上的小烷基取代基将RCM导向六元环形成,但交叉易位导致二聚体占据了更大的烷基基团。对于没有官能团X的前体,获得了相似的结果。在具有不对称的OTBS或OMe基团的不对称取代的萜类前体(R = Et,R 1 = Me)的情况下,可以控制RCM形成大环的类mb体,即具有出色的E选择性分离。通过简化模型底物的量子化学计算进一步研究了取代基的作用。基于这些结果,提出了机械原理。