Catalytic Asymmetric Synthesis of the Pentacyclic Core of (+)-Citrinadin A

The synthesis of the pentacylic core of (+)-citrinadin A is described. Our strategy harnesses the power of palladium-catalyzed trimethylenemethane chemistry (Pd-TMM) to form the key spirooxindole motif in a catalytic, asymmetric fashion. Upon the conversion of this spirooxindole to a vinyl epoxide electrophile, the piperidine ring is directly added via a diastereoselective metalation followed by an S_N2′ addition. The final ring of the pentacyclic core is then formed through an intramolecular S_N2 displacement of the resulting activated alcohol.