Total Synthesis of (-)-Gephylotoxin 223AB via Asymmetric 1,3-Dipolar Cycloaddition

研究了以手性烯丙基醚为亲偶极试剂对硝基酮进行不对称1,3-偶极环加成反应，并应用于(-)-coniine和(+)- monmonorine I的对映选择性合成。环和非环硝基与(s)-3-苄基氧基-1-庚烯反应，分别优先生成（2R,3aS）和(3S,5R)-异恶唑烷基衍生物（3:1），应用过渡态内烷氧基更活泼的构象预测。这些环加合物分别被对映转化为(-)-coniine和(+)- monmonorine I。

Asymmetric 1,3-dipolar cycloaddition of nitrones by using a chiral allyl ether as a dipolarophile and application to an enantioselective synthesis of (-)-coniine and (+)-monomorine I has been investigated. The cyclic and acyclic nitrones were allowed to react with (s)-3-benzyloxy-1-heptene, resulting in the preferential formation (3:1) of the (2R,3aS)-and (3S,5R)-isoxazolidine derivatives, respectively, predicted by application of the inside alkoxy more reactive conformation in a transition state. These cycloadducts were enantiomerically converted to (-)-coniine and (+)-monomorine I,respectively.