Attempts To Improve the Overall Stereoselectivity of the Ireland−Claisen Rearrangement
作者:Chi-Li Chen、Kosuke Namba、Yoshito Kishi
DOI:10.1021/ol8027225
日期:2009.1.15
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 °C and (2) E-6 isomerizes to Z-6 at 80 °C, thereby allowing the transformation of 5 into 7 in an almost quantitative
着眼于 [3,3]-σ 重排的过渡态中存在的空间效应,底物5已被设计为提高爱尔兰-克莱森重排的整体立体选择性。实验发现,(1) 只有Z -6在 80 °C 下重排为7和 (2) E -6 在 80 °C 下异构化为Z -6,从而允许5以几乎定量的方式转化为7屈服。为了说明这种方法的有用性,给出了两个额外的例子。