Synthetic studies on lactonamycins: synthesis of the model BCDEF aglycon.

The lactonamycin model aglycon 4 was synthesized from the trihalogenated benzene derivative 10. Ethynyltetraol 6 was prepared from 10 via carbon elongations, oxidative demethylation, a cycloaddition reaction with the diene derived from homophthalic anhydride, and dihydroxylation. Final E- and F-ring constructions from 6 were realized via a palladium-catalyzed cyclization−methoxycarbonylation, a stereoselective methanol addition, and lactonization, leading to the production of 4.