Stereocontrolled Synthesis of the A/B-Ring Fragment of Gambieric Acid B: Reassignment of the Absolute Configuration of the Polycyclic Ether Region

Stereocontrolled synthesis of the A/B-ring fragment of the originally assigned structure of gambieric acid B and its possible diastereomers has been accomplished. Detailed comparison of their 1H and 13C NMR data with those of the corresponding moiety of the natural product culminated in a stereochemical reassignment of the absolute configuration of the polycyclic ether region of gambieric acid B.