Enantioselective Total Synthesis of (+)-Arboridinine.

The enantioselective total synthesis of cage-shaped alkaloid (+)-arboridinine is reported. The synthesis takes advantage of the stereoselective double-Mannich reaction to rapidly construct the aza[3.3.1]bicyclic core along with two quaternary stereocenters of the alkaloid. Key steps for the present synthesis include an enantioselective Michael addition establishing the original chiral center at C10 and intramolecular dearomative alkylation forging the cage-shaped ring system found in arboridinine, as well as creating the requisite quaternary carbon center at C3. The bridgehead hydroxyl moiety at C11 was installed through a late-stage cobalt-catalyzed decarboxylative acetoxylation reaction. This strategy enables a 14-step asymmetric total synthesis of (+)-arboridinine from the readily available starting materials with most of the transformations performed on the decagram scale.