A novel extension of the Stork–Jung vinylsilane Robinson annelation procedure for the introduction of the cyclohexene of guanacastepene

A new annelation procedure has been developed in a model system to introduce the cyclohexene ring of guanacastepene. Cyclohexenone 16 is prepared by sequential methylation and alkylation with allylic iodide 15. One-pot epoxidation, protodesilylation and hydrolysis of the THP forms dione 19, which cyclizes with NaOMe to 24 in 57% overall yield. Reduction, Mitsunobu inversion, and selective oxidation of the primary alcohol forms model 29. Phenyldimethylsilyl allylic iodide 36 is easier to make and more stable than trimethylsilyl allylic iodide 6 used by Stork.