We report the first total synthesis of (−)‐17‐nor‐excelsinidine, a zwitterionic monoterpene indole alkaloid that displays an unusual N4−C16 connection. Inspired by the postulated biosynthesis, we explored an oxidative coupling approach from the geissoschizine framework to forge the key ammonium–acetate connection. Two strategies allowed us to achieve this goal, namely an intramolecular nucleophilic substitution on a 16‐chlorolactam with the N4 nitrogen atom or a direct I₂‐mediated N4−C16 oxidative coupling from the enolate of geissoschizine.

中文翻译：

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生物启发性的Geissoschizine骨架的氧化环化反应，可合成（-）-17-nor-Excelsinidine

我们报告了（−）-17-nor-excelsinidine的第一个全合成，这是一种两性离子单萜吲哚生物碱，显示出异常的N4-C16连接。受假定的生物合成的启发，我们探索了Geissoschizine骨架的氧化偶联方法，以建立关键的醋酸铵连接。有两种策略使我们得以实现这一目标，即在16-氯内酰胺上用N4氮原子进行分子内亲核取代或从Geissoschizine的烯醇化物中直接进行I ₂介导的N4-C16氧化偶联。