Synthesis of the racemic tetracyclic core of CP-225,917—a model compound lacking the sidearms of the natural product

Compound 3, representing the tetracyclic core structure of CP-225,917, was prepared from bridgehead olefin 9, which was first converted into ketone 13. Peterson olefination then gave 15, and this was elaborated into the anhydride 19, from which crystalline 3 was reached by a sequence of deprotection and oxidation steps.