Direct C−H Trifluoromethylation of Quinoxalin-2(1H )-ones under Transition-Metal-Free Conditions

Copper-catalyzed chemoselective C-H functionalization of quinoxalin-2(1H)-ones with hexafluoroisopropanol

An unexpected three-component reaction of quinoxalin-2(1H)-ones, tert-butyl peroxybenzoate (TBPB), and hexafluoroisopropanol (HFIP) is described. Under CuBr-catalyzed and TBPB-oxidized conditions, a variety of hydroxyhexafluoroisobutylated quinoxalin-2(1H)-ones were formed. Furthermore, the first hexafluoroisopropoxylation of the quinoxalin-2(1H)-ones with HFIP is also demonstrated with Cu2O as the catalyst and PhI(OAc)2 as the oxidant. These new transformations of HFIP furnish previously unknown and potentially useful fluorinated quinoxalin-2(1H)-one derivatives.

The C3-H Bond Functionalization of Quinoxalin-2(1H)-Ones With Hypervalent Iodine(III) Reagents

The modification of quinoxalin-2(1H)-ones via direct C-H bond functionalization has begun to receive widespread attention, due to quinoxalin-2(1H)-one derivatives' various biological activities and pharmaceutical properties. This mini review concentrates on the accomplishments of arylation, trifluoromethylation, alkylation, and alkoxylation of quinoxalin-2(1H)-ones with hypervalent iodine(III) reagents as reaction partners or oxidants. The reaction conditions and mechanisms are compared and discussed in detail.

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.

Metal-free late-stage C(sp2)-H functionalization of N-aryl amines with various sodium salts

Metal-free consecutive C(sp2)-X (X = Cl, Br, S, N) bond formations of N-aryl amines (cyclic, fused, carbamate, and aminium radicals) were achieved under mild conditions using [bis(trifluoroacetoxy)iodo]benzene (PIFA) and simple nonharmful sodium salts. This direct and selective C(sp2)-H functionalization showed excellent functional group compatibility, cost effectiveness, and late-stage applicability for the synthesis of biologically active natural products. Two mechanisms were proposed to explain the ortho- or para-preference, as well as the accelerating effect of CH3NO2.

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.

Metal-free C3–H acylation of quinoxalin-2(1H)-ones with α-oxo-carboxylic acids

Direct C3–H acylation of quinoxalin-2(1H)-ones with α-oxocarboxylic acids under thermo conditions promoted by PIDA has been achieved in a moderate to good yield in a very fast manner.

Transition-metal free direct C–H functionalization of quinoxalin-2(1H)-ones with oxamic acids leading to 3-carbamoyl quinoxalin-2(1H)-ones

A practical transition-metal free decarboxylative coupling reaction of oxamic acids with quinoxalin-2(1H)-ones has been developed under mild conditions.

Visible-light-promoted acridine red catalyzed aerobic oxidative decarboxylative acylation of α-oxo-carboxylic acids with quinoxalin-2(1H)-ones

Visible-light-mediated procedure has been developed for the synthesis of 3-acyl quinoxalin-2(1H)-ones through acridine red catalyzed decarboxylative acylation of α-oxo-carboxylic acids with quinoxalin-2(1H)-ones.

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.

tert-Butylhydroperoxide (TBHP) mediated oxidative cross-dehydrogenative coupling of quinoxalin-2(1H)-ones with 4-hydroxycoumarins, 4-hydroxy-6-methyl-2-pyrone and 2-hydroxy-1,4-naphthoquinone under metal-free conditions

We report an efficient and atom-economical method of C-3 functionalization of quinoxalin-2(1H)-ones with 4-hydroxycoumarins, 4-hydroxy-6-methyl-2-pyrone, and 2-hydroxy-1,4-naphthoquinone via the free radical cross-coupling pathway under metal-free conditions. tert-Butylhydroperoxide (TBHP) smoothly promotes the reaction furnishing the cross-dehydrogenative coupling (CDC) products in very good to excellent yields. The protocol neither uses any toxic reagents nor metal catalysts to carry out the reaction, and all the products have been obtained without column chromatography purification. Different radical trapping experiments with 2,2,6,6-tetramethylpiperidine-1-oxyl, butylated hydroxytoluene, and diphenyl ethylene confirm the involvement of radicals.

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.

Electrochemical trifluoromethylation/semipinacol rearrangement sequences of alkenyl alcohols: synthesis of β-CF3-substituted ketones

Electrochemical oxidative radical trifluoromethylation/semipinacol rearrangement sequences of alkenyl alcohols were developed in this study. This approach is environmentally benign and uses the shelf-stable Langlois reagent as a trifluoromethyl radical precursor and electrons as the oxidizing reagents. The present protocol offers a facile route to prepare β-trifluoromethylated ketone derivatives.

Covalent Organic Frameworks: A Sustainable Photocatalyst toward Visible-Light-Accelerated C3 Arylation and Alkylation of Quinoxalin-2(1H)-ones

A practical and scalable protocol for visible-light-accelerated arylation and alkylation of quinoxalin-2(1H)-ones with hydrazines is reported. In this protocol, a hydrazone-based two-dimensional covalent organic frameworks (2D-COF-1) was employed as the heterogeneous photocatalyst (PC). Due to its excellent photocatalytic properties, good chemical stability and heterogeneous nature, the present method exhibits high efficiency, good functional group tolerance, easy scalability and remarkable catalyst reusability. More importantly, it provides an alternative way that allows rapid access to various C3 arylated or alkylated quinoxalin-2(1H)-ones in a greener and sustainable manner.

Electrochemical Arylation of Electron-Deficient Arenes through Reductive Activation

An electrochemical method has been developed to achieve arylation of electron-deficient arenes through reductive activation. Various electron-deficient arenes and aryldiazonium tetrafluoroborates are amenable to this transformation within the conditions of an undivided cell, providing the desired products in up to 92 % yield. Instead of preparing diazonium reagents, these reactions can begin from anilines, and they can be carried out in one pot. Electron paramagnetic resonance studies indicate that cathodic reduction of quinoxaline occurs using the transformation. Moreover, cyclic voltammetry indicates that both quinoxaline and aryl diazonium salt have relatively low reduction potentials, which suggests they can be activated through reduction during the reaction.

Ring-opening C(sp3)–C coupling of cyclobutanone oxime esters for the preparation of cyanoalkyl containing heterocycles enabled by photocatalysis

A ring-opening C(sp³)–C coupling of cyclobutanone oxime esters for the preparation of cyanoalkyl containing heterocycles was realized under visible-light or sunlight irradiation.

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.

Transition-metal-free decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-ones with α,α-difluoroarylacetic acids

A facile and efficient transition-metal-free decarboxylative radical coupling reaction of α,α-difluoroarylacetic acids with quinoxalin-2(1H)-ones has been developed under mild conditions.

Visible-light induced decarboxylative alkylation of quinoxalin-2(1H)-ones at the C3-position

3-Alkylquinoxalin-2(1H)-ones are synthesized via direct alkylation of quinoxalin-2(1H)-ones at the C3 position under visible light irradiation.

Insights into the mechanisms of Ag-catalyzed synthesis of CF3-substituted heterocycles via [3+2]-cycloaddition from α-trifluoromethylated methyl isocyanides: effects of DBU and exploration of diastereoselectivity

The diastereoselectivity of [3+2]-cycloaddition can be reasonably explained by the analysis of steric hindrance using DFT calculations.