Access to C5-Sulfonylated Tetrahydropyridazines via Photoinduced Cascade Sulfonylation-Cyclization of N-Cinnamyl Aldehyde Hydrazones

Direct installation of a sulfonyl functional group into the C5-position of tetrahydropyridazine was achieved using N'-benzylidene-N-cinnamylacetohydrazide as a new building skeleton via the photocatalytic carbosulfonylation/annulation procedure. Various substituted C5-sulfonylated tetrahydropyridazines were obtained in good to excellent yields employing aryl- or alkylsulfonyl chlorides as the sulfonyl radical sources. This reaction was realized through the selective addition of sulfonyl radical to the C2 position of cinnamyl followed by the 6-endo-trig annulation to the hydrazone CH═N bond.