Photocatalytic Cascade Radical Sulfonamidation/Cyclization of N -Isopentenyl Aldehyde Hydrazones to Access C5-Sulfonamidated Tetrahydropyridazines

A photoinduced cascade radical sulfonamidation/cyclization of N-isopentenyl aldehyde hydrazones with N-sulfonylaminopyridinium salts using 4CzIPN as the photocatalyst was developed. The sulfonylamino group was selectively installed into the tetrahydropyridazine core rather than the side chain, providing a series of C5-sulfonamidated tetrahydropyridazines in 61-87% yields.