Access to 1-aryl-pyrazolin-5-ones <i>via</i> photoinduced chemoselective cyclization of <i>N</i>-methacrylo aldehyde hydrazones

A photocatalytic sulfamoylation/5-<i>endo-trig</i> cyclization of (<i>E</i>)-<i>N</i>'-arylidene-<i>N</i>-phenylmethacrylohydrazides with sulfamoyl chlorides was developed. The chemoselective intramolecular addition of the carbon-centered radical intermediate to the CN bond in the hydrazone motif gave the sulfamoylated pyrazolin-5-one. Besides, sulfonyl chlorides are also suitable reaction partners to access sulfonylated pyrazolin-5-ones. This approach is characterized by mild reaction conditions, broad substrates scope, excellent selectivity and the late-stage modification of drug molecules.