Divergent Entry to Gelsedine-Type Alkaloids: Total Syntheses of (-)-Gelsedilam, (-)-Gelsenicine, (-)-Gelsedine, and (-)-Gelsemoxonine.

The gelsedine-type alkaloids possess a common oxabicyclo[3.2.2]nonane core and spiro- N-methoxyindolinone moiety along with a diversely functionalized heterocycle embedded in the compact framework. Herein we disclose a divergent entry to gelsedine-type alkaloids that hinges on rapid assembly of the common core by the orchestrated application of an asymmetric Michael addition, a tandem oxidation/aldol cyclization, and a pinacol rearrangement and generation of the structural diversity via a late-stage heterocyclization. The power of this strategy has been demonstrated through very short total syntheses of four gelsedine-type alkaloids: gelsedilam, gelsenicine, gelsedine, and gelsemoxonine.