Photocatalytic Functionalization of Dihydroquinoxalin‐2‐Ones with Pyrazolones

A visible‐light photoredox functionalization of 3,4‐dihydro‐quinoxalin‐2‐ones with pyrazolones using an inexpensive organophotoredox catalyst is described. The reaction uses 9,10‐phenanthrenedione as photocatalyst, a very simple and cheap photocatalyst, a HP single Blue LED (455 nm) as visible‐light source and oxygen from air as terminal oxidant, obtaining the corresponding acetylated pyrazoles with good yields. The reaction can be extended to other nitrogen heterocycles such as 5‐aminopyrazoles with good results.