Total Synthesis of (−)-Spinosyn A: Examination of Structural Features That Govern the Stereoselectivity of the Key Transannular Diels−Alder Reaction
作者:SusAnn M. Winbush、Dustin J. Mergott、William R. Roush
DOI:10.1021/jo7024515
日期:2008.3.1
The TDA cyclizations of 12 (which lacks the C(8)-OTBS unit of 9), 13 (which lacks the C(6)-Br substituent of 12), and 14 (which lacks the C(6)-Br and C(21)-Et substituents of 12) were also studied. Macrocycles 12 and 13 served as precursors to (−)-spinosyn A and the (−)-spinosyn A aglycon (34), respectively. It is striking that substrates 12−14 give very similar distributions of transannular Diels−Alder
描述了在环过环Diels-Alder反应中导致(-)-spinosynyn A的十氢化物作为-茚并二烯核心的立体化学控制元素的研究。最初的研究集中在大环戊烯9上,该大环戊烯9包括C(6)-Br和C(8)-OTBS取代基。在1的3,3-烯丙基应变相互作用中,在不利的TS-2中涉及C(6)和C(8)取代基,在9的环加成反应中观察到极好的选择性(> 95:5)。主要的环加成22( - ) -中的一个正式的合成中使用的多杀菌素A.的TDA环化12(其缺少C(8)的-OTBS单元9),13(其缺少C(6)-Br取代基的12),和14(其缺少C(6)-Br和C(21)的取代基-Et 12)也进行了研究。大环12和13分别用作(-)-多杀菌素A和(-)-多杀菌素A糖苷配基(34)的前体。令人吃惊的是基片12 - 14给出非常相似跨环狄尔斯-阿尔德cycloadducts的分布,表明C(6)-Br和C(2