Total synthesis of (±)-nakamurol-A and its 13-epimer: tentative assignment of the C-13 relative configuration

A general approach to the structure of thelepogan-type diterpenoids has been developed and its application to the first total synthesis of (±)-nakamurol-A is described. The key steps involve: (i) a diastereoselective dimethylzinc addition to an endocyclic enone followed by enolate trapping; (ii) a Sakurai allylation of an exocyclic enone; and (iii) a Wacker chemoselective oxidation. The 1H NMR data for the synthetic nakamurol-A and its C-13 epimer allow a tentative assignment of the relative configuration at C-13 of the natural product.