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 (1)H and (13)C 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.