Unforeseen 1,2-Aryl Shift in Tetraarylpyrrolo[3,2-b]pyrroles Triggered by Oxidative Aromatic Coupling

Tetraarylpyrrolo[3,2-b]pyrroles (TAPPs) possessing [1,1'-biphenyl]-2-yl substituents attached to the pyrrolic nitrogen atoms undergo selective double dehydrogenative cyclization accompanied by twofold 1,2-aryl migration under oxidative aromatic coupling conditions. The structure of the product of the rearrangement has been unambiguously confirmed by X-ray crystallography, and the reaction pathway is supported by density functional theory (DFT) calculations. Six-membered ring formation (requiring rearrangement of aryl substituents around the core) is energetically preferred over seven-membered ring closure, and a 1,2-aryl shift occurs via arenium cation intermediate.