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.