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. An efficient, racemic, and enantioselective total synthesis of the diterpene waihoensene is presented. Key steps are a radical cyclization, a Pauson–Khand reaction, and an asymmetric allylic decarboxylative allylation (AAA) reaction to obtain optical active material.