A simple transformation of the eight-carbon side chain of a natural spirostan sapogenin into the cephalostatin north 1 spiroketal moiety is described. This methodology, based on an intramolecular hydrogen abstraction reaction promoted by alkoxy radicals, permits the synthesis of C-22 and C-25 stereoisomers of the dioxaspiro[4.4]nonane cephalostatin ring system. The acid-catalyzed isomerization of the
描述了将天然螺旋体sapogenin的八个碳原子的侧链简单地转化为headostatin north 1 spiroketal部分。这种方法基于烷氧基自由基促进的分子内氢提取反应,可以合成二恶螺环[4.4]壬烷头戴抑素环系统的C-22和C-25立体异构体。研究了不同异构体中螺中心的酸催化异构化。[反应:看文字]