A Straightforward Transformation of ent ‐Trachylobanoic Acid Into Functionalized ent ‐Kauranes Under Conditions of Modified Prevost–Woodward Reaction

ABSTRACT ent ‐Trachylobanoic acid is a readily available pentacyclic diterpenoid that includes a strained cyclopropane ring in its structure which can be used as a synthetic handle toward other biogenetically‐related diterpenoids of ent ‐series. We present in the current paper a selective, one‐step transformation of ent ‐trachylobanoic acid into functionalized derivatives of ent ‐kauranic structure under the action of a modified Prevost–Woodward reagent in hot acetic acid. Adding a slight excess of water to the reaction mixture brings about the selective formation of 12α‐hydroxy‐16α‐acetoxy‐ ent ‐kauran‐19‐oic acid—a useful intermediate for the synthesis of other C‐12 functionalized ent ‐kauranes. Alkaline treatment of the latter triggers an unusual Grob‐like fragmentation toward a seco ‐kauranic compound.