Synthesis of the spirocyclic framework of sesterterpenoid natural products.

A convergent synthetic route to the sesterterpenoid framework of the bioactive phorbaketal and alotaketal natural product families has been established. The synthetic approach hinges on a Hosomi-Sakurai coupling of complex acetal and allylsilane coupling partners, followed by DDQ-promoted oxidative cyclization of highly unsaturated advanced intermediates. This robust synthetic approach enables further investigations into the members of these natural product families and readily provides access to analogues for biological testing.