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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.

The functionalization at the C-3 position of 3,4-dihydroquinoxalin-2-one core has been significantly targeted over the last years. Several nucleophilic, electrophilic as well as radical catalytic functionalization of these nitrogen heterocycles have been reported. Usually, the more convenient methods are the direct photoredox functionalizations which use mild, green and sustainable conditions.

Quinoxalin‐2(1H)‐one is an important class of nitrogen heterocycle in medicinal and pharmaceutical industry, which became a synthetic target in organic chemistry in recent years. This review covers the recent advances in the functionalization of this particular nitrogen heterocycle through photocatalysis.