Visible Light-Induced Cyclization of <i>N</i> -Arylmethacrylohydrazides and Hydroxamic Acid Derivatives toward δ-Amidoalkylated Pyrazol-5-ones via 1,5-Hydrogen Atom Transfer

A photoinduced radical cascade cyclization of <i>N</i>-arylmethacrylohydrazides and hydroxamic acid derivatives for the synthesis of pyrazol-5-ones via 1,5-hydrogen atom transfer was developed. A series of pyrazol-5-ones was obtained in good yield with a broad substrate scope and excellent functional group compatibility. The procedure was also applied to the late-stage modification of natural products and drug molecules.