Formal Total Synthesis of Atropurpuran

Atropurpuran, isolated from the roots of Aconitum
hemsleyanum, is a non-alkaloidal diterpene which possesses
a unique pentacyclic skeleton that contains an unprecedented tetracyclo­[5.3.3.04,9.04,12]­tridecane unit. We report herein the formal
total synthesis of atropurpuran. The key features of our synthetic
route are a high diastereoselective construction of the tri- and tetrasubstituted
carbons (i.e., C4, C5, C10, and C20) through an Yb-catalyzed Mukaiyama
aldol reaction in an aqueous medium and a one-pot operation including
an intramolecular Diels–Alder reaction/ring-closing metathesis
to construct the unique pentacyclic skeleton of atropurpuran.