Synthesis of the racemic tetracyclic core of CP-225,917: use of a strain-assisted Cope rearrangement

Norbornene was converted via diketone 23 into the strained lactone 27; this was rearranged thermally to lactone 28, from which point the complete oxygenated core of CP-225,917 is accessible by deprotection and oxidation steps, including a new method for converting a furan system into a hydroxy butenolide.