Total Syntheses of 2,2‘-<i>epi</i>-Cytoskyrin A, Rugulosin, and the Alleged Structure of Rugulin

The total syntheses of 2,2‘-epi-cytoskyrin A, rugulosin, and the alleged structure of rugulin are described. These naturally occurring bisanthraquinones and their relatives are characterized by novel molecular architectures at the core, at which lies a more or less complete, cage-like structural motif termed “skyrane”. The strategies developed for their total synthesis feature a cascade sequence called the “cytoskyrin cascade” and deliver these molecules in short order and in a stereoselective manner.