Studies towards Simalikalactone D and Quassimarin: Construction of an Advanced Pentacyclic Intermediate

An advanced pentacyclic intermediate, amenable to further elaboration into the target molecules simalikalactone D and quassimarin, has been synthesized from ( S )‐(+)‐carvone in 21 steps and with an overall yield of 12 %. The synthesis is efficient, stereocontrolled, enantiospecific, and chirality productive, creating eight new chiral centres in pentacycle, and should provide opportunities for rapid access to simalikalactone D analogues and other bioactive quassinoids. The reaction sequence involves a regioselective bishydroxylmethylation, a stereocontrolled epoxidation, an epoxymethano‐bridge formation, a 1,3‐sigmatropic rearrangement and an intramolecular Diels–Alder reaction as the key steps.