Total Synthesis of (±)-Larutienine B and (±)-Melokhanine B, D, E, F, and H

We report a versatile and scalable strategy for the concise syntheses of six C2-spirooxindole alkaloids in 13-15 steps. This synthetic approach features an oxidative aza-Diels-Alder cycloaddition and a retro-Mannich/Mannich reaction to build the tetracyclic ring system alongside a formal Michael addition facilitated by neighboring group participation to install the side chain. Notably, the first total synthesis of larutienine B has been accomplished. The outlined strategy offers a complementary solution for addressing the stereocontrol difficulties in syntheses of eburnane-type alkaloids.