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.