Synthesis of s-Indacene Derivatives by Double Robinson-Type Cyclopentene Annulation

Michael reactions of 2,5-dioxocyclohexane-1,4-dicarboxylates with methyl vinyl ketone yield bis-adducts that can be further cyclized in a Robinson-type annulation to give s-indacene derivatives as single diastereomers. The carboxylate functions of this scaffold can be deprotected and subsequently decarboxylated to yield tricyclic products with a central aromatic ring.