Synthesis of a Fully Functionalized Chasmanine AF-Ring Fragment.

C19-Diterpenoid alkaloids (C19 DTAs) represent a large family of structurally and biologically complex natural products. Within this class, C6-oxidized natural products have remained largely unsynthesized. Herein, we report an expedient synthesis of the fully functionalized AF-ring fragment of chasmanine. Key to our approach was the use of a Piancatelli rearrangement to access the F ring, which then enabled a Mg alkoxide-templated [4+2] cycloaddition to form the AF-ring fragment. We also report a bench-stable oxidative nitrilation reagent for the conversion of aldehydes into nitriles.