A Concise Synthesis of Forskolin

We report a 24-step synthesis of ()-forskolin, which delivered hundred-milligram quantities of this complex diterpene in one pass. Transformations key to our approach include: (a) a strategic allylic transposition, (b) stepwise assembly of a sterically encumbered isoxazole ring, and (c) citric acid-modified Upjohn dihydroxylation of a resilient tetrasubstituted olefin. We demonstrate that the developed route has an exciting potential for the preparation of new forskolin analogs inaccessible by semisynthesis.