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 3.2.1bicyclic system found in the ent-kaurane skeleton was realized with two overbred intermediates. Wagner–Meerwein rearrangement of the 3.2.1bicyclic system yields the beyerane skeleton of isosteviol.