Skeletal Editing of Pyridine to Pyridazine via ANRORC (Addition of Nucleophile, Ring Opening, and Ring Closing) Mechanism

Abstract We report a pyridine-to-pyridazine skeletal editing strategy that enables a formal CN-to-NN atom-pair exchange from readily available pyridines. Key to this transformation is hydrazine-mediated ring opening of N-(2,4-dinitrophenyl)pyridinium salts, followed by mCPBA-promoted oxidation to a 5-diazenylpenta-2,4-dienal intermediate that undergoes 6π-electrocyclization and oxidative deformylation to deliver pyridazines. This method features mild reaction conditions, broad substrate scope, late-stage applicability, and gram-scale scalability.