Tandem Oxidative Dearomatizations of Diphenylanthracene Atropisomers.

The first examples of tandem oxidative dearomatizations of 9,10-diphenylanthracene atropisomers with ,'- formyl substituents are presented. In the presence of KMnO, their stereoselective tandem double oxidation and spirocyclization mainly afford the or dearomatized 9,10-diphthalide anthracenes. Using Pinnick's reagent and depending on the conditions, the oxidation can mainly lead to the corresponding or diacids in good yields or to three oxidation products. An unprecedented further oxidative ring expansion toward dibenzo[,]oxepines is also reported.