A Homo‐Mannich Reaction Strategy Enables Collective Access to Ibophyllidine, <i>Aspidosperma</i>, <i>Kopsia</i>, and <i>Melodinus</i> Alkaloids
Dan Jiang, Peng Tang, Hongbing Xiong, Shuai Lei, Yulian Zhang, Chongzhou Zhang, Ling He, Han‐Yue Qiu, Min Zhang
Abstract
We report here a homo-Mannich reaction of cyclopropanol with an iminium ion, generated by an asymmetric allylic dearomatization of indole, to construct a tricyclic hydrocarbazole core, which is shared by a variety of monoterpenoid indole alkaloids across families. Through this approach, an all-carbon quaternary stereogenic center as well as an allyl and a ketone group were installed. Using this functionalized hydrocarbazole as the structural platform, D ring and E rings of different sizes (i.e., five-, six-, and seven-membered) were successively or simultaneously assembled, leading to a collective asymmetric synthesis of seven alkaloids belonging to the ibophyllidine, Aspidosperma, Kopsia, and Melodinus alkaloid families.