Palladium mediated C–H activation in the field of terpenoids: synthesis of rostratone

We present results, which indicate that Pd-mediated C–H bond activation can be used under mild conditions for the remote functionalization of C-4 methyl groups of molecules with different terpenoid-like skeletons containing six- or seven-membered A rings. This procedure has allowed us to complete a novel strategy for the synthesis of γ-dioxygenated terpenoids in three stages: (i) selective epoxidation of commercial polyenes, (ii) titanium(III)-catalyzed cyclization of epoxypolyprenes, and (iii) Pd-mediated remote functionalization of equatorial methyl groups. This strategy has proved to be useful for the synthesis of the natural labdane rostratone (1).