Direct oxidative C H amination of quinoxalinones under copper-organic framework catalysis

Photoinduced Dehydrogenative Amination of Quinoxalin-2(1H)-ones with Air as an Oxidant

A facile and eco-friendly photoinduced dehydrogenative amination of quinoxalin-2(1H)-ones with aliphatic amines without any metal, strong oxidant, and photocatalyst has been established for the first time. This reaction proceeding efficiently with air as the sole oxidant at room temperature obtains a wide range of 3-aminoquinoxaline-2(1H)-ones in high yields with excellent functional group tolerance. The mechanistic studies show an interesting involvement of quinoxalin-2(1H)-ones as a photosensitizer, which eliminates the requirement for external photocatalysts.

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

In recent years, Web of Science has published nearly one hundred reports per year on quinoxalin-2(1H)-ones, which have attracted great interest due to their wide applications in pharmaceutical and materials fields, especially in recyclable heterogeneous catalytic reactions for direct C-H functionalisation. This review summarises for the first time the methods and reaction mechanisms of heterogeneous catalytic reactions of quinoxalin-2(1H)-ones, including six major types of heterogeneous catalysts involved. The heterogeneous reactions of quinoxalin-2(1H)-ones are summarised by classifying different types of catalytic materials (graphitic phase carbon nitride, MOF, COF, ion exchange resin, piezoelectric materials, and microsphere catalysis). In addition, this review discusses the future development of heterogeneous catalytic reactions of quinoxalin-2(1H)-ones, including the construction of C-B/Si/P/R_F/X/Se bonds by heterogeneous catalytic reactions, the enrichment of heterogeneous catalysts such as metal oxides, graphene-based composites, doped metal nanoparticles, and molecular sieve-based porous materials, asymmetric synthesis, and other areas. The aim of this review is to contribute to the development of green and sustainable heterogeneous reaction methods for quinoxalin-2(1H)-ones with applications in materials chemistry and pharmacology.

Regioselective C-3-alkylation of quinoxalin-2(1H)-ones via C-N bond cleavage of amine derived Katritzky salts enabled by continuous-flow photoredox catalysis

An efficient, transition metal-free visible-light-driven continuous-flow C-3-alkylation of quinoxalin-2(1H)-ones has been demonstrated by employing Katritzky salts as alkylating agents in the presence of eosin-y as a photoredox catalyst and DIPEA as a base at room temperature. The present protocol was accomplished by utilizing abundant and inexpensive alkyl amine (both primary and secondary alkyl) and as well as this a few amino acid feedstocks were converted into their corresponding redox-active pyridinium salts and subsequently into alkyl radicals. A wide variety of C-3-alkylated quinoxalin-2(1H)-ones were synthesized in moderate to high yields. Further this environmentally benign protocol is carried out in a PFA (Perfluoroalkoxy alkane) capillary based micro reactor under blue LED irradiation, enabling excellent yields (72% to 91%) and shorter reaction times (0.81 min) as compared to a batch system (16 h).

Electrochemical Oxidative C-H Arylation of Quinoxalin(on)es with Arylhydrazine Hydrochlorides under Mild Conditions

A practical and scalable protocol for electrochemical arylation of quinoxalin(on)es with arylhydrazine hydrochlorides under mild conditions has been developed. This method exhibits high efficiency, easy scalability, and broad functional group tolerance. Various quinoxalin(on)es and arylhydrazines underwent this transformation smoothly in an undivided cell, providing the corresponding aryl-substituted quinoxalin(on)es in moderate to good yields. A radical mechanism is involved in this arylation reaction.

Organic-acid catalysed Minisci-type arylation of heterocycles with aryl acyl peroxides

A metal-free method for the Minisci-type arylation of heterocycles with aryl acyl peroxides has been reported. This strategy enables the rapid and simple synthesis of a series of Minisci-type adducts...

Metal–organic framework (MOF)-, covalent-organic framework (COF)-, and porous-organic polymers (POP)-catalyzed selective C–H bond activation and functionalization reactions

The review summarizes the state-of-the-art of C–H active transformations over crystalline and amorphous porous materials as new emerging heterogeneous (photo)catalysts.

Metal-free regioselective nitration of quinoxalin-2(1H)-ones with tert-butyl nitrite

A metal-free coupling of quinoxalin-2(1H)-ones with tert-butyl nitrite has been developed. Distinctly from the previous functionalization of quinoxalin-2(1H)-ones, this nitration reaction took place selectively at the C7 or C5 position of the phenyl ring, affording a series of 7-nitro and 5-nitro quinoxalin-2(1H)-ones in moderate to good yields. Preliminary mechanistic studies revealed that the reaction may involve a radical process.

Synthesis of (E)-Quinoxalinone Oximes through a Multicomponent Reaction under Mild Conditions

Herein, a novel method for the gram-scale synthesis of (E)-quinoxalinone oximes through a multicomponent reaction under mild conditions is described. Such a transformation was performed under transition-metal-free conditions, affording (E)-oximes in a moderate-to-good yield through recrystallization. Our methodology demonstrates a successful combination of a Mannich-type reaction and radical coupling, providing a green and practical approach for the synthesis of potentially bioactive quinoxalinone-containing molecules.

CuII- and CoII-Based MOFs: {[La2Cu3(µ-H2O)(ODA)6(H2O)3]∙3H2O}n and {[La2Co3(ODA)6(H2O)6]∙12H2O}n. The Relevance of Physicochemical Properties on the Catalytic Aerobic Oxidation of Cyclohexene

The aerobic oxidation of cyclohexene was done using the heterometallic metal organic frameworks (MOFs) {[La2Cu3(μ-H2O)(ODA)6(H2O)3]⋅3H2O}n (LaCuODA)) (1) and {[La2Co3(ODA)6(H2O)6]∙12H2O}n (LaCoODA) (2) as catalysts, in solvent free conditions (ODA, oxydiacetic acid). After 24 h of reaction, the catalytic system showed that LaCoODA had a better catalytic performance than that of LaCuODA (conversion 85% and 67%). The structures of both catalysts were very similar, showing channels running along the c axis. The physicochemical properties of both MOFs were determined to understand the catalytic performance. The Langmuir surface area of LaCoODA was shown to be greater than that of LaCuODA, while the acid strength and acid sites were greater for LaCuODA. On the other hand, the redox potential of the active sites was related to CoII/CoIII in LaCoODA and CuII/CuI in LaCuODA. Therefore, it is concluded that the Langmuir surface area and the redox potentials were more important than the acid strength and acid sites of the studied MOFs, in terms of the referred catalytic performance. Finally, the reaction conditions were also shown to play an important role in the catalytic performance of the studied systems. Especially, the type of oxidant and the way to supply it to the reaction medium influenced the catalytic results.

Photoinitiated decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-ones with potassium 2,2-difluoro-2-arylacetates in water

An efficient and green strategy for the preparation of C3-difluoroarylmethylated quinoxalin-2(1H)-one via a visible-light-induced decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-one with potassium 2,2-difluoro-2-arylacetate in water at room temperature was developed. This photoinduced reaction generated the desired products in good yields under simple and mild conditions.

Visible-light-induced aerobic C3-H fluoroalkoxylation of quinoxalin-2(1H)-ones with fluoroalkyl alcohols

A novel and efficient method of visible-light-induced C3-H fluoroalkoxylation of quinoxalin-2(1H)-ones with fluoroalkyl alcohols is developed. This approach uses readily available fluoroalkyl alcohols as fluoroalkoxylation reagents and displays a wide substrate scope, providing the fluoroalkoxylated products in moderate to good yields. Compared with the previous method, such a transformation uses oxygen as an oxidant, which avoids the utilization of plenty of PhI(TFA)2. In addition, this strategy also gives a practical tool for the rapid synthesis of histamine-4 receptor antagonist and new N-containing bidentate ligands. A radical mechanism was suggested according to the results of control experiments.

Transition-metal-free direct C-3 cyanation of quinoxalin-2(1H)-ones with ammonium thiocyanate as the “CN” source

A practical protocol for TBHP-mediated oxidative C–H cyanation of quinoxalin-2(1H)-ones utilizing ammonium thiocyanate as the cyanide source has been developed under metal free conditions.

Photocatalyst-, metal- and additive-free, direct C–H arylation of quinoxalin-2(1H)-ones with aryl acyl peroxides induced by visible light

A visible light-mediated direct C–H arylation of quinoxalin-2(1H)-ones with aryl acyl peroxides has been developed.

Recent advances in the direct functionalization of quinoxalin-2(1H)-ones

The direct C3-functionalization of quinoxalin-2(1H)-ones via C-H bond activation has recently attracted considerable attention, due to their diverse biological activities and chemical properties. This review will focus on the recent achievements, mainly including arylation, alkylation, acylation, alkoxycarbonylation, amination, amidation and phosphonation of quinoxalin-2(1H)-ones. Their mechanisms are also discussed.

The visible-light-triggered regioselective alkylation of quinoxalin-2(1H)-ones via decarboxylation coupling

An efficient protocol to synthesize 3-alkylated quinoxalin-2(1H)-ones through photocatalytic decarboxylation coupling reactions of quinoxalin-2(1H)-ones with N-hydroxyphthalimide ester was developed.

Influence of the channel size of isostructural 3d–4f MOFs on the catalytic aerobic oxidation of cycloalkenes

The present work reports a new group of heterogeneous catalysts with a 3D structure, CuLnIDA, {[Cu₃Ln₂(IDA)₆]·8H₂O} (Ln: La^III, Gd^III or Yb^III), with an organic linker (H₂IDA: iminodiacetic acid).

Visible-light-promoted direct C–H/S–H cross-coupling of quinoxalin-2(1H)-ones with thiols leading to 3-sulfenylated quinoxalin-2(1H)-ones in air

A new and efficient visible-light-mediated strategy has been developed for the synthesis of 3-sulfenylated quinoxalin-2(1H)-ones via rhodamine B catalyzed C–H/S–H cross-coupling of quinoxalin-2(1H)-ones with thiols in air at room temperature.

Heterometallic CuII/LnIII polymers active in the catalytic aerobic oxidation of cycloalkenes under solvent-free conditions

Heterometallic 3d-4f inorganic polymers were prepared using 3,5 pyridinedicarboxylic acid (H2PDC), {[CuLn2(PDC)2(SO4)2(H2O)6]·H2O}n (Ln: SmIII, CuSmPDC, EuIII, CuEuPDC, GdIII, and CuGdPDC). These catalysts are active in the aerobic oxidation of cycloalkenes under solvent-free conditions, with a conversion for the oxidation of cyclohexene of 71% after one hour of the reaction, and a TOF value of 1438 h-1 for CuSmPDC. On the other hand, the oxidation of cycloheptene and cyclooctene exhibited slightly lower conversions of 52% and 47%, and TOF values of 1053 and 159 h-1 after 1 and 6 hours of the reaction, respectively. The radical mechanism for the oxidation reaction of cyclohexene was assessed by Raman and EPR spectroscopy. The first evidenced the formation of Cu-O2 adducts and the second permitted is to observe the presence of the oxygen centered radical species, which act as initiators of the reaction chain to generate the products. An increase in the temperature of the reaction correlates with the adduct formation, and with the enhancement of the oxidation reaction.