Synthetic studies toward jatrophane diterpenes from Euphorbia characias. Enantioselective synthesis of (-)-15-O-acetyl-3-O-propionyl-17-norcharaciol.

The enantioselective synthesis of (+)-17-norcharaciol is described. An uncatalyzed intramolecular carbonyl-ene reaction and a ring-closing metathesis were used as key C/C-connecting transformations to assemble the trans-bicyclo[10.3.0]pentadecane norditerpenoid core. We also report the evolution of our synthetic strategy toward the fully substituted characiol skeleton and the experiences from this venture.