Perylenequinone natural products: evolution of the total synthesis of cercosporin.

The evolution of the first total synthesis of perylenequinone cercosporin is described. The key features developed during these efforts include a biscuprate epoxide alkylation, installation of the methylidene acetal, palladium-catalyzed O-arylation, and C3,C3'-decarbonylation. Due to the rapid atropisomerization of the helical axis of cercosporin (at 37 degrees C), the sequencing of these transformations was critical. To this end, the developed protocol enabled the formation of a key advanced intermediate on preparative scale absent any atropisomerization. Furthermore, the O-arylation proved to be general, and the strategy was used in an improved synthesis of a helical chiral perylenequinone structure.