Photocatalytic Functionalization of Dihydroquinoxalin‐2‐Ones with Pyrazolones

Abstract

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.

Electron‐Deficient Phenanthrenequinone Derivative for Photoactivated Hydrogen Atom Transfer Mediated Oxidation of Secondary Alcohols

“…PQ is known to undergo oxidative degradation to dibenzoic acid in the presence of a strong base [40] or an excess of H 2 O 2 in either acidic or basic conditions. [41] As aerobic oxidation of the hydroquinone produces equimolar amount of H 2 O 2 , [20] we believe that PQ-CF 3 is prone to oxidative degradation even when a trace amount of H 2 O 2 is present in a concentrated solution. When PQH 2 -CF 3 was oxidized with NaIO 4 under argon, [42] the reaction yielded quickly and selectively PQ-CF 3 , resulting in the final yield of 81 % over four steps (Scheme 2).…”

“…[13] Especially excited state anthraquinones have been extensively studied and utilized as oxidative photocatalysts, [14] but over the last few years, 9,10-phenanthrenequinone (PQ) has caught increasing attention. Most of the PQ-catalyzed reactions reported to this date proceed via SET pathway, [15][16][17][18][19][20] and so far, only a few HAT mediated processes have been developed. A fairly common HAT pathway accessed by visible-light-excited PQ (PQ*) proceeds via the formation of an acyl radical from an aldehyde substrate.…”

Catalytic Nucleophilic and Electrophilic Functionalization of Dihydroquinoxalin‐2‐ones

“…In 2022, our research group reported the reaction between 4‐substituted‐3,4‐dihydroquinoxalin‐2‐ones 1 and pyrazol‐3‐ones 17 under photoredox conditions (Scheme 8). [15] After the optimization process, we realized that the best photocatalyst to conduct this transformation was 9,10‐phenanthrenedione due to its high performance, its cost and the simplicity of the process [16] . To aid isolation and characterization of the product, it was crucial to perform an acetylation of the enolate using acetic anhydride once the photochemical reaction was complete.…”

Organophotoredox 1,6-Addition of 3,4-Dihydroquinoxalin-2-ones to para-Quinone Methides Using Visible Light

“…When Eosin Y (entry 2) or 2,4,6-triphenylpyrylium tetrafluoroborate (entry 3) were used as photocatalysts, the efficiency of the reaction was worse, and 3aa was gained with much lower yield. A complex reaction mixture was observed when 4-CzIPN (2,4,5,6-tetrakis­(9 H -carbazol-9-yl) isophthalonitrile) was used, while product 3aa was not observed when 9,10-phenanthrenedione , was tested (entry 4 and 5, respectively). Delightfully, we could quantify by 1 H NMR the expected product 3aa in 94% yield after 19 h of irradiation when Fukuzumi’s photocatalyst ([Mes-Acr-Me]­[BF 4 ]) was employed.…”