Synthesis of the Functionalized Tricyclic Core of Lactonamycin by Oxidative Dearomatization

[reaction: see text] We report in this Letter a synthesis of the densely oxygenated CDEF ring system (27) corresponding to that found in the recently discovered antibiotic lactonamycin. The key steps in the synthesis consist of an intramolecular Wessely oxidative lactonization of acid 18, followed by a hydroxyl-directed epoxidation of enol ether 21.