Novel Synthesis of the ABC Rings of Solanoeclepin A

A stereocontrolled synthesis of the ABC rings of solanoeclepin A has been achieved. The seven-membered ring B was synthesized by an intramolecular Prins-ene reaction between an aldehyde and an enyne-dicobalthexacarbonyl complex. The acetylene in this synthesis plays multiple roles: to join the A and C rings, to allow stereoselective cyclization via dicobalthexacarbonyl complexation, and to facilitate Nicholas cation stabilization followed by deprotonation to form an endo-cyclic olefin (NicholasPrins cyclization).