Total synthesis of (-)-scabrolide A and (-)-yonarolide.

The complete account of the total syntheses of scabrolide A and yonarolide is disclosed. This article describes an initial approach involving a bio-inspired macrocyclization/transannular Diels-Alder cascade, which ultimately failed due to undesired reactivity during macrocycle construction. Next, the evolution of a second and third strategy, which both involve an initial intramolecular Diels-Alder reaction followed by a late-stage closure of the seven-membered ring of scabrolide A are detailed. The third strategy was first validated on a simplified system, but problems were encountered during a key [2 + 2] photocycloaddition on the fully elaborated system. An olefin protection strategy was employed to circumvent this problem, ultimately leading to the completion of the first total synthesis of scabrolide A and the closely related natural product yonarolide.