Photocatalytic Carbosulfonylation/Cyclization of N -Homoallyl and N -Allyl Aldehyde Hydrazones toward Sulfonylated Tetrahydropyridazines and Dihydropyrazoles.

N '-Benzylidene- N -homoallylacetohydrazides were designed and synthesized as novel skeletons for the construction of functionalized tetrahydropyridazines. A series of aryl- and alkylsulfonylated tetrahydropyridazines were obtained in yields of up to 94% employing sulfonyl chlorides as the sulfonyl radical sources under visible-light irradiation. Besides, sulfonylated dihydropyrazoles were also produced from N -allyl- N '-benzylideneacetohydrazides. Mechanistic investigations indicated that both energy transfer and single electron transfer processes were involved in accomplishing the radical 6/5- endo - trig cyclization to the C═N bond.