Divergent Total Synthesis of Euphoranginol C, Euphoranginone D, ent-Trachyloban-3β-ol, ent-Trachyloban-3-one, Excoecarin E, and ent-16α-Hydroxy-atisane-3-one.

A divergent synthetic approach to biogenetically related diterpenoids such as ent -kauranes, ent -trachylobanes, ent -beyerane, and ent -atisane has been developed. The unified synthetic route involves the De Mayo reaction to rapidly generate the bicyclo[3.2.1]-octane moiety of ent -kaurane. The key reactions also include bioinspired nucleophilic cyclopropanation generating the [3.2.1.0 2,7 ]-tricyclic core of ent -trachylobane and regioselective cyclopropane fragmentation furnishing ent -beyerane and ent -atisane through the nucleophilic attack and protonation of the cyclopropane ring. This strategy enables the asymmetric total syntheses of six diterpenoids from the commercially available geraniol.