Total Syntheses of Scabrolide A and Yonarolide.

The concise total syntheses of oxidized norcembranoid terpenoids (-)-scabrolide A and (-)-yonarolide have been accomplished in 10 and 11 steps, respectively. The carbocyclic skeleton was efficiently constructed from two chiral-pool-derived fragments, including a [5,5]-bicyclic lactone accessed through a powerful Ni-catalyzed pentannulation of functionalized cyclopentenone with methylenecyclopropane and subsequent fragmentation. Additional features included a Liebeskind-Srogl coupling, induction of a cyclization/elimination cascade by a zinc-amido base, and installation of a sensitive enedione motif by late-stage γ-oxidation.