Enantioselective synthesis of neocarzinostatin chromophore aglycon

An enantioselective approach to the synthesis of neocarzinostatin chromophore aglycon is described. The substance is a difficult synthetic target due to the strain, structural complexity and high reactivity of the chromophore core. The allylic transposition problem can be avoided by epoxidation of the five-membered ring olefin in a modification of an earlier strategy. Epoxidation also retains a favorable trajectory for the intramolecular acetylide addition reaction and delays until the final stage many of the instability issues which beset earlier strategies.