An efficient synthesis of the carbocyclic core of zoanthenol

A concise strategy for the synthesis of the carbocyclic portion of zoanthenol is disclosed. The key step involves a 6-endo radical-mediated conjugate addition that constructs the quaternary stereocenter at C(12) and closes the B ring in a stereoselective manner. The synthesis of the C-ring fragment uses an enantioselective desymmetrization to simultaneously establish the absolute stereochemistry of two vicinal quaternary stereocenters. In only 17 steps from known compounds, the route affords an ABC ring system containing all three quaternary stereocenters and appropriate functionality to complete the synthesis of zoanthenol.