Total Synthesis of Luotonin A and Rutaecarpine from an Aldimine via the Designed Cyclization

The total synthesis of rutaecarpine (1) and luotonin A (2) is described through controlled cyclization of a common aldimine intermediate 5 derived from ethyl-2-aminocinnamate and quinazolinone-2-carbaldehyde. The cyanide-mediated imino-Stetter reaction of aldimine 5 provided the corresponding indole derivative 3, from which the total synthesis of rutaecarpine (1) was completed via the formation of a 6-membered C-ring. On the other hand, microwave-assisted thermal 6π-electrocyclization of the common intermediate 5, followed by the formation of a 5-membered C'-ring, allowed the completion of the total synthesis of luotonin A (2).