Cyclobutylidenecyclopropane: New Synthesis and Use in 1,3-Dipolar Cycloadditions − A Direct Route to Spirocyclopropane-Annulated Azepinone Derivatives
作者:Armin de Meijere、Malte von Seebach、Sergei I. Kozhushkov、Roland Boese、Dieter Bläser、Stefano Cicchi、Tula Dimoulas、Alberto Brandi
DOI:10.1002/1099-0690(200110)2001:20<3789::aid-ejoc3789>3.0.co;2-o
日期:2001.10
Cyclobutylidenecyclopropane (7) was prepared in multigram quantities by a new three-step sequence starting from ethyl cyclobutanecarboxylate (4) (39% overall yield). 1,3-Dipolar cycloadditions of phenyl- (9), pyridyl- (10), and the newly prepared (four steps, 43% overall yield) spirocyclic nitrone 11 onto 7 resulted in the regioselective formation of the corresponding adducts 15−17, with the spirobutane
从环丁烷羧酸乙酯 (4) (39% 总产率) 开始,通过新的三步顺序制备了数克数量的环亚丁基环丙烷 (7)。苯基- (9)、吡啶基- (10) 和新制备的(四步,总产率 43%)螺环硝酮 11-7 的 1,3-偶极环加成导致相应加合物 15-17 的区域选择性形成,螺丁烷部分与恶唑烷环中的氧原子相邻,产率分别为 52%、84% 和 48%。在快速真空热解条件下,环加合物 15-17 经历热重排,四元环打开,分别以 32%、30% 和 19% 的产率提供螺环丙烷化氮杂酮 21-23。在 17 的情况下,也分离出吲哚里西酮 25(产率 13%)。