Photocatalytic radical amination/cyclization of N-allyl and N-homoallyl aldehyde hydrazones: access to sulfonaminated pyrazoles and tetrahydropyridazines

A photocatalytic strategy for the sulfonamidation/cyclization of N -allyl and N -homoallyl aldehyde hydrazones has been developed with N -aminopyridinium salts as sulfonylamino radical precursors. This transformation enables efficient access to sulfonylamino-substituted pyrazoles and tetrahydropyridazines under mild conditions. This protocol features broad substrate compatibility, consistently affording good to excellent yields and exhibiting excellent scalability. Preliminary mechanistic studies support a sulfonamino radical-mediated cascade cyclization pathway for this transformation. Notably, the N -aminopyridinium salts serve a dual role as both sulfonamination reagents and hydrogen-atom transfer mediators, enabling the one-step synthesis of sulfonylamidated pyrazoles. A visible-light-driven photocatalytic radical cascade enables the efficient sulfonamination/cyclization of N -allyl and N -homoallyl aldehyde hydrazones. Bench-stable N -aminopyridinium salts serve dual roles as sulfonamino radical precursors and hydrogen-atom transfer mediators, affording sulfonaminated pyrazoles and tetrahydropyridazines under mild and green conditions.