Oxidation Potential Gap (ΔE ox ): The Hidden Parameter in Redox Chemistry.

Oxidative biaryl coupling of aryls with different electronic features generally fails. However, this has not been systematically studied via theoretical analysis, and thus, the crucial factor governing coupling efficiency remains unclear. Herein, we propose that the "oxidation potential gap (ΔE ox )" is a key parameter in predicting the efficiency of an intramolecular oxidative coupling reaction, with ΔE ox defined as a difference in the oxidation potentials of the relevant aromatic rings. Our experimental and computational analyses revealed that the efficiency of an aromatic intramolecular coupling reaction correlates with the activation energy (ΔE ≠ ) of C-C bond formation of the radical cation intermediates. Furthermore, ΔE ≠ correlates with ΔE ox . Therefore, we demonstrate the tuning of ΔE ox by attaching cleavable extra electron-donating/-withdrawing groups, enabling the rational synthesis of a phenanthridone skeleton using aromatic rings with an electronic gap.