A Homo‐Mannich Reaction Strategy Enables Collective Access to Ibophyllidine, Aspidosperma, Kopsia, and Melodinus Alkaloids

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. A homo‐Mannich reaction of cyclopropanol with an iminium ion, generated by an asymmetric allylic dearomatization of indole, has been developed to construct a tricyclic hydrocarbazole core. This approach enables a collective asymmetric synthesis of ibophyllidine, Aspidosperma, Kopsia, and Melodinus alkaloids having either a five‐, six‐, or seven‐membered E ring.