Enantioselective Total Synthesis of the Guaianolide (−)-Dehydrocostus Lactone by Enediyne Metathesis

Abstract

The hydroazulene core of the bioactive sesquiterpenoid (−)-dehydrocostus lactone was generated by domino enediyne metathesis. A triple hydroboration/oxidation of the resultant conjugated triene installed three out of four stereogenic centers of the target in a single step. The enantiopure acyclic metathesis substrate was readily available by an asymmetric anti aldol reaction. Masking of the γ-lactone as an acetal allowed for an efficient completion of the synthesis through late-stage double carbonyl olefination.