Photocatalytic Furan-to-Pyridazine Skeletal Editing

Pyridazines are privileged diazine scaffolds in pharmaceuticals and agrochemicals, yet their synthesis remains hampered by the inherent limitations of conventional condensation methods and recent pyridine-based skeletal editing approaches: poor regioselectivity, narrow substrate scope, and requirement for additional oxidation steps. Herein, we report the visible-light-mediated skeletal editing of furans to pyridazines via formal O-to-NN atom-pair exchange using hydrazine hydrate as the dinitrogen source. This ring expansion operates under metal-free, room-temperature, aerobic conditions and bypasses conventional 1,4-dicarbonyl condensation pathways. Mechanistic studies and DFT calculations show that water suppresses hydrazine-mediated photocatalyst quenching and promotes six-membered cyclization, while ambient air acts as the terminal oxidant for selective aromatization. The method exhibits broad functional group tolerance, enables late-stage diversification of complex molecules, and scales efficiently to gram scale without yield or selectivity loss. Notably, it affords di-, tri-, and tetrasubstituted pyridazines with complete regiocontrol governed by furan substitution, providing a complementary, sustainable platform for pyridazine synthesis from biomass feedstocks.