Synthesis of the Cyclohepta[e]hydrindane Core of the Marine Homoverrucosane Diterpenoid Gagunin E.

The synthesis of the A-B-cis B-C-trans annulated cyclohepta[e]hydrindane core of gagunin E with a fully elaborated B-C ring segment has been achieved. Using an adaptable A ring building block, the B ring was annulated by (4 + 2)-cycloaddition and the C ring by ring-closing metathesis. The angular methyl groups were attached by electrophilic cyclopropanation-ring opening.