A New,Stereoselective Approach to the [3.3.3]Propellane System: Synthesis of (±)-modhephene. Preliminary communication

The unusual propellane skeleton of the sesquiterpene modhephene ( 1 ) has been synthesized starting from cyclopentenone ( 2 ). The key step 6 → 7 is an efficient and highly stereoselective intramolecular thermal ene-reaction. Further elaboration of the propellane 7 gave the enone 10 which had been previously converted to (±)-modhephene ( 1 ) in three steps.