Vinylogous urethanes in alkaloid synthesis. Applications to the synthesis of racemic indolizidine 209B and its (5R*,8S *,8aS *)-(±) diastereomer, and to (−)-indolizidine 209B †
作者:Joseph P. Michael、David Gravestock
DOI:10.1039/b001853h
日期:——
indolizidine (indolizidine 209B) (±)-1 and its hitherto unknown (5R*,8S*,8aS*) diastereomer (±)-20 were accomplished in eight steps from pyrrolidine-2-thione and ethyl oct-2-enoate. Key steps included cyclisations exploiting the nucleophilicity of vinylogous urethanes derived from ethyl (2E)-1-[1-(2-hydroxyethyl)hexyl]pyrrolidin-2-ylidene}acetate 8, and stereoselective reduction of the carbon–carbon
外消旋体(5 R *,8 R *,8a S *)-8-甲基-5-戊基吲哚并咪唑(吲哚并立定209B)(±)-1及其迄今未知的(5 R *,8 S *,8a S *)的合成非对映体(±)-20由8个步骤完成吡咯烷-2-硫酮 和 辛-2-烯酸乙酯。关键步骤包括利用衍生自乙烯基类氨基甲酸酯的亲核性进行环化反应(2 E)-1- [1- [1-(2-羟乙基)己基]吡咯烷-2-亚乙基}乙酸乙酯 8,立体选择减少 双环乙烯基碳-碳双键的合成 氨基甲酸酯 11。对路线的对映体选择性修饰,涉及初始共轭加成(R)-(+)- N-苄基-1-苯基乙胺的阴离子与叔丁基(2E)-辛-2-烯酸叔丁酯的合成导致(-)-吲哚并啶209B的形式合成。