TANDEM USE OF COBALT-MEDIATED REACTIONS TO SYNTHESIZE (-EPOXYDICTYMENE, A DITERPENE CONTAINING A TRANS-FUSED 5-5-RING-SYSTEM())

The diterpene (+)-epoxydictymene has been synthesized in 20 steps usin g the asymmetry of (R)-pulegone and several substrate-controlled diast ereoselective reactions to prepare the natural product in its natural configuration. Three of the four rings were assembled with two consecu tive intramolecular reactions involving dicobalt hexacarbonyl complexe s of alkynes: a Lewis acid-promoted Nicholas reaction and a Pauson-Kha nd reaction. The construction of the strained trans-3-oxabicyclo[3.3.0 ]octane ring system of the natural product presented a significant cha llenge. To this end, several radical and anionic cyclizations were stu died, the latter leading to (+)-epoxydictymene.