Chen Chi-Li, Namba Kosuke, Kishi Yoshito
Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA.
Org Lett. 2009 Jan 15;11(2):409-12. doi: 10.1021/ol8027225.
With focus on the steric effects present in the transition states for the [3,3]-sigmatropic rearrangement, the substrate 5 has been designed to improve the overall stereoselectivity of the Ireland-Claisen rearrangement. Experimentally, it has been found that (1) only Z-6 rearranges to 7 at 80 degrees C and (2) E-6 isomerizes to Z-6 at 80 degrees C, thereby allowing the transformation of 5 into 7 in an almost quantitative yield. To illustrate the usefulness of this approach, two additional examples are given.
着眼于[3,3] - 迁移重排过渡态中存在的空间效应，设计了底物5以提高爱尔兰 - 克莱森重排的整体立体选择性。实验发现：（1）仅Z - 6在80℃下重排为7；（2）E - 6在80℃下异构化为Z - 6，从而使5几乎定量地转化为7。为说明该方法的实用性，又给出了另外两个例子。
