Highly Stereoselectivetrans Addition of π-Type Nucleophiles to a BicyclicN-Acyliminium Ion – Application to the Synthesis of Indolizidine and Pyrrolizidine Alkaloids
作者:Hamid Dhimane、Corinne Vanucci-Bacqué、Louis Hamon、Gérard Lhommet
DOI:10.1002/(sici)1099-0690(199809)1998:9<1955::aid-ejoc1955>3.0.co;2-u
日期:1998.9
usefulness of this stereoselective access to trans-2,5-disubstituted pyrrolidines was illustrated by formal syntheses of 3,5-disubstituted indolizidine toxins, starting from 5-allyltetrahydropyrrolo[1,2-c]oxazol-3-one 2a. Moreover, an enantiodivergent synthesis of the pyrrolizidine alkaloids (+) and (–)-xenovenine was achieved starting from the same chiral building block 2a.
对映体纯双环 5-乙氧基四氢吡咯并 [1,2-c] 恶唑-3-one 1b 由已知的甲苯磺酸酯 4 分两步制备,甲苯磺酸酯 4 很容易从 (S)-焦谷氨酸中获得。在路易斯酸存在下从 1b 原位生成的 N-acyliminium 离子 (I) 与各种硅烷化 π 型亲核试剂的捕获选择性地产生反式加合物 2。这种立体选择性获取反式 2,5 的有用性-二取代的吡咯烷通过 3,5-二取代的吲哚里西啶毒素的正式合成来说明,从 5-烯丙基四氢吡咯并 [1,2-c] 恶唑-3-one 2a 开始。此外,从相同的手性结构单元 2a 开始,实现了吡咯里西啶生物碱 (+) 和 (-)-xenovenine 的对映发散合成。