Total Synthesis of the Melodinus Alkaloid (±)-Melohemsine K

The first total synthesis of the novel Melodinus alkaloid melohemsine K is described in five steps from known precursors. The key reaction of the synthesis is a tandem enamine formation/retro-aza-Michael reaction/Diels–Alder cycloaddition/intramolecular lactamization reaction cascade between indole-fused azepine and aldehyde precursors, forging the critical CDE tricyclic system. The synthesis provided a general approach to novel Melodinus alkaloids.