Synthesis of (-)-nakamurol A and assignment of absolute configuration of diterpenoid (+)-nakamurol A

The total synthesis of the enantiomer of the marine sponge diterpenoid nakamurol A and determination of the absolute configuration of this natural product are reported. This first synthetic entry to thelepogane-type diterpenoids involves the use of the bicyclic enone (-)-3, which after a tandem difunctionalization process and elongation of the side chain leads to the formation of the ketone (-)-13. From (-)-13, two approaches to ent-nakamurol A (1) are reported: the straightforward but nonselective way, by reaction with vinylmagnesium bromide, and a longer but stereocontrolled route, through the primary allylic alcohol 20, which is submitted to a Sharpless epoxidation followed by a tellurium-promoted reductive-epoxide ring-opening cascade reaction.