Catalytic Asymmetric Total Synthesis of (-)-Galanthamine and (-)-Lycoramine

The catalytic asymmetric total syntheses of (-)-galanthamine (1) and (-)-lycoramine (2) have been achieved by using a conceptually new strategy featuring two metal-catalyzed reactions as the key steps. A new method for the construction of 3,4-fused benzofurans has been developed through a palladium-catalyzed intramolecular Larock annulation reaction, which was successfully applied to the construction of the ABD tricyclic skeleton of 1 and 2. To achieve the asymmetric synthesis of 1 and 2, a Sc-III/N,N-dioxide complex was used to catalyze the enantioselective conjugate addition of 3-alkyl-substituted benzofuranone to methyl vinyl ketone for the construction of a chiral quaternary carbon center.