Total Synthesis of (-)-Oridonin: An Interrupted Nazarov Approach.

An enantioselective total synthesis of (-)-oridonin is accomplished based on a key interrupted Nazarov reaction. The stereochemistry of the Nazarov/Hosomi-Sakurai cascade was first explored to forge a tetracyclic skeleton with challenging quaternary carbons. A delicate sequence of two ring-rearrangements and late-stage redox manipulations was carried out to achieve the de novo synthesis of this highly oxidized ent-kauranoid.