General Methodology for the Topologically Selective Preparation of Linear and Nonlinear Tricyclopentanoids of Hirsutane and Isocomene Type via a Claisen Rearrangement / Cyclopentene Annulation Sequence. Total Synthesis of (±)- Epiisocomene

The intramolecular cyclopentene annulation methodology which combines the cyclopropanation of dienic diazoketones and the vinylcyclopropane rearrangement is utilized to synthesize linear tricyclopentanoids of the hirsutane class or nonlinear members of the isocomene class. The requisite diene precursors, endocyclic or exocyclic, respectively, are obtained from acylcyclopentenes via orthoester Claisen rearrangement of either allyl or propargyl alcohols. The scope and the generality of the method are indicated and experimental details are presented pertaining to the synthesis of precursory dienes for hirsutane and isocomene sesquiterpenes. Full details are disclosed concerning the total synthesis of epiisocomene and the synthesis of linearly fused precursors to coriolin sesquiterpenes.