Studies toward total synthesis of divergolides C and D.

A facile synthesis of the western segment of divergolides C and D has been developed. Exploratory studies with two disconnections, i.e., C4-C5 vs C5-C6, for elaboration of the ansa bridge to the sterically demanding hexasubstituted naphthalenic aromatic core using a chiral synthon assembled from D-glucose via a stereoselective Johnson orthoester rearrangement is described. The studies set the stage for the completion of the total synthesis of the biologically important novel ansamycins, divergolides C and D, and their structural congeners.