Total Synthesis of the Diterpene Waihoensene

A racemic and scalable enantioselective total synthesis of (+)‐waihoensene was accomplished. (+)‐Waihoensene belongs to the diterpene natural product family, and it features an angular triquinane substructure motif. Its tetracyclic [6.5.5.5]backbone is all‐cis‐fused, containing six contiguous stereocenters, four of which are quaternary. These structural features were efficiently installed by means of a diastereoselective radical cyclization, followed by an intramolecular Pauson–Khand reaction, a diastereoselective α‐alkylation, and a diastereoselective 1,4‐addition reaction. Enantioselectivity was introduced at an early stage, by an asymmetric palladium catalyzed decarboxylative allylation reaction on gram scale.