Synthesis of ent-Kaurane and Beyerane Diterpenoids by Controlled Fragmentations of Overbred Intermediates

Efficient access to minimally oxidized members of the ent‐kaurane and beyerane class of terpenes has been achieved by using a polyene cyclization precursor designed to directly yield oxidation at the axial C19‐methyl group. Construction of the [3.2.1]bicyclic system found in the ent‐kaurane skeleton was realized with two overbred intermediates. Wagner–Meerwein rearrangement of the [3.2.1]bicyclic system yields the beyerane skeleton of isosteviol.