Visible-Light-Induced Recyclable g-C3N4 Catalyzed C–H Hydroxylation of Quinoxalin-2(1H)-ones

Abstract

A visible-light-promoted hydroxylation of quinoxalin-2(1H)-ones using recyclable graphitic carbon nitride (g-C3N4) as a heterogeneous photocatalyst was developed. This protocol enabled the selective synthesis of various hydroxyl-containing quinoxalin-2(1H)-ones in good to excellent yields under an ambient air atmosphere. Importantly, this heterogeneous catalyst can be used at least 6 times without significant loss of activity.

Recent Developments in Direct C–H Functionalization of Quinoxalin-2(1H)-Ones via Heterogeneous Catalysis Reactions

“…The presence of aromatic amines was confirmed by electrospray ionisation (ESI) mass spectrometry. In 2022, Peng and co-workers proposed a heterogeneous visible light-induced direct C-H hydroxylation of quinoxalin-2(1H)-ones (Scheme 5) [42]. The method uses g-C3N4 as a photocatalyst under air conditions and yields a variety of 3-hydroxyquinoxalin-2(1H)-ones by simple washing and filtration.…”

“…However, this approach has the disadvantage of using large excesses of environmentally unfriendly inorganic strong oxidants and harsh reaction conditions, which generates chemical waste and increases manufacturing costs [43]. In 2022, Peng and co-workers proposed a heterogeneous visible light-induced direct C-H hydroxylation of quinoxalin-2(1H)-ones (Scheme 5) [42]. The method uses g-C 3 N 4 as a photocatalyst under air conditions and yields a variety of 3-hydroxyquinoxalin-2(1H)-ones by simple washing and filtration.…”

“…However, this approach has the disadvantage of using large excesses of environmentally unfriendly inorganic strong oxidants and harsh reaction conditions, which generates chemical waste and increases manufacturing costs [43]. Based on controlled experiments and references in the literature, the reaction mechanism shown in Scheme 6 was proposed [42]. First, g-C3N4 is excited by visible light to produce an electron in the conduction band (CB) and a hole in the valence band (VB).…”

“…The VB hole then gains an electron from the thiol 2b to form the thiyl radical cation 4b through a single electron transfer process. At the same time, an electron from the CB Based on controlled experiments and references in the literature, the reaction mechanism shown in Scheme 6 was proposed [42]. First, g-C 3 N 4 is excited by visible light to produce an electron in the conduction band (CB) and a hole in the valence band (VB).…”

“…Based on controlled experiments and references in the literature, the reaction mechanism shown in Scheme 6 was proposed [ 42 ]. First, g-C 3 N 4 is excited by visible light to produce an electron in the conduction band (CB) and a hole in the valence band (VB).…”