We describe an enantioselective total synthesis of the nonahydroxylated sesquiterpenoid euonyminol, the dihydro-β-agarofuran nucleus of the macrocyclic terpenoid alkaloids known as the cathedulins. Key features of the synthetic sequence include a highly diastereoselective intramolecular alkene oxyalkylation to establish the C10 quaternary center, an intramolecular aldol-dehydration to access the tricyclic