De novo synthesis of a galacto-papulacandin moiety via an iterative dihydroxylation strategy

A short and highly efficient route to both the pyranose and furanose forms of a galacto-papulacandin ring system has been developed. The key to the overall transformation is the sequential two osmium-catalyzed dihydroxylation reactions of substituted 2,4-dienone. The resulting tetrol can be efficiently transformed into the two spiroketal moieties of galacto-papulacandin, which can also be inter-converted via acid catalyzed equilibration.