Asymmetric Total Syntheses of Aspidodasycarpine, Lonicerine, and the Proposed Structure of Lanciferine

Aspidodasycarpine and lonicerine are a pair of epimeric aspidophylline-type alkaloids bearing, vicinal quaternary. C7 and C16. The first and enantioselective total syntheses of these molecules are described here. A Ru-catalyzed asymmetric transfer hydrogenation established the first stereocenter.: An Au-promoted Toste cyclization was exploited to assemble the bridged tetracyclic core and define the geometry of the exocyclic olefin; electron deficient (p-CF3C6H4)(3)P was a suitable ligand for this transformation. An aldol condensation followed by an intramolecular indole C3 alkylation constructed the adjacent quaternary C7 and C16 diastereoselectively, leading to a pentacyclic lactol as an advanced common intermediate for synthesizing both alkaloids. The proposed structure of lanciferine, a highly oxidized congener of aspidodasycarpine, was synthesized from the lactol by tuning the oxidation states of various carbons.