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.