Synthesis of a pentacyclic lactone related to quinovaic acid and emmolactone using an anionic polycyclization strategy

In an effort to discover a versatile and convergent synthesis of pentacylic triterpenes, we have synthesized a tetracyclic enone via a highly stereocontrolled cycloaddition between a Nazarov precursor and a cyclohexenone followed by an aldol condensation. Introduction of a C14 nitrile was made by hydrocyanation on a protected derivative of this tetracyclic enone. Reduction and subsequent hydrolysis of the latter intermediate concluded this expedient synthesis of a pentacyclic lactone.