Transition-Metal and Solvent-Free Oxidative C–H Fluoroalkoxylation of Quinoxalinones with Fluoroalkyl Alcohols

Visible-light-induced synthesis of heteroaryl C-glycosides via decarboxylative C-H glycosylation

A photoredox promoted decarboxylative C-H glycosylation has been developed for the synthesis of heteroaryl C-glycosides. This methodology is characterized by its exceedingly simple reaction system, high diastereoselectivity and good functional group tolerance. Moreover, this innovative approach circumvents the need for high temperatures, transition metals, and photocatalysts, providing an environmentally friendly, straightforward, and efficient protocol.

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.

Metal-free C-3 selective C(sp2)-C(sp3) heteroarylation of anilines with imidazo[1,2-a]pyridine derivatives via cross-dehydrogenative coupling

A general and straightforward method for the regioselective construction of C-3 heteroaryl-containing imidazo[1,2-a]pyridines via cross-dehydrogenative coupling under transition-metal-free conditions has been reported, utilizing N,N-dimethylaniline as the methylenation source and furnishing the C(sp²)-C(sp³) functionalized products in good to excellent yields. Mechanism studies indicate that a radical pathway is responsible for this transformation.

Direct Access to Strained Fused Dihalo-Aziridino Quinoxalinones via C3-Alkylation Followed by Tandem Cyclization

Quinoxalinones are a privileged class of compounds, and their structural framework is found in many bioactive compounds, natural compounds, and pharmaceuticals. Quinoxalinone is a promising scaffold for different types of functionalization, and the slight modification of the quinoxalinone skeleton is known to offer a wide range of compounds for drug discovery. Owing to the importance of the quinoxalinone scaffold, we have developed a base-mediated protocol for the C3-alkylation of quinoxalinone followed by tandem cyclization to access novel types of strenuous and fused dihalo-aziridino-quinoxalinone heterocycles via the construction of C-C and C-N bonds. The protocol proved to be simple and practical to access desired fused quinoxalinone heterocycles in excellent yields (up to 98% yield). As an application, the highly functionalized fused dihalo-aziridino-quinoxalinone molecule has been further utilized for mono-dehalogenation under visible light irradiation and selective amide reduction. Moreover, the protocol has also been demonstrated on a gram scale.

Selectfluor-Mediated Regioselective C-3 Alkoxylation, Amination, Sulfenylation, and Selenylation of Quinoxalin-2(1H)-ones

A Selectfluor-promoted oxidative coupling of quinoxalin-2(1H)-ones with alcohols, amines, thiols, and selenols leading to the formation of C-O, C-N, C-S, and C-Se bonds has been developed. The protocol provided good to excellent (53-95%) yields of a wide range of quinoxalin-2(1H)-ones decorated with alkoxy, alkylamino, alkylthio, and arylselenyl groups at the C3-position under metal- and photocatalyst-free conditions. The reaction is believed to proceed through a radical pathway. A broad substrate scope including bioactive molecules, mild reaction conditions, readily available coupling partners, high yields, scalability, step-economy, and metal- and photocatalyst-free conditions are the highlighting features of the method. The synthetic utility of the developed protocol was demonstrated by gram-scale synthesis, C3-alkoxylation of quinoxaline-2(1H)-one with natural alcohols, and synthesis of aldose reductase (ALR2) inhibitor and histamine-4 receptor antagonist in good yields.

Annulation Reaction of Quinoxalin-2(1H)-ones Initiated by Electrochemical Decarboxylation of N-Arylglycines

A new methodology for the synthesis of tetrahydroimidazo[1,5-a]quinoxalin-4(5H)-ones has been accomplished through annulation of quinoxalin-2(1H)-ones initiated by electrochemical decarboxylation of N-arylglycines catalyzed by ferrocene. With a pair of oxidative and reductive processes occurring among the substrates and intermediates instead of on the electrodes, the electricity consumption was decreased.

Acid-Promoted Direct C-H Carbamoylation at the C-3 Position of Quinoxalin-2(1H)-ones with Isocyanide in Water

Described herein is a concise and practical direct amidation at the C-3 position of quinoxalin-2(1H)-ones through an acid-promoted carbamoylation with isocyanide in water. In this conversion, environmentally friendly water and commercial inexpensive isocyanide were used as a solvent and carbamoylation reagent, respectively. This study not only provides a green and efficient strategy for the construction of 3-carbamoylquinoxalin-2(1H)-one derivatives that can be applied to the synthesis of druglike structures but also expands the application of isocyanide in organic chemistry.

C-H Diselenation and Monoselenation of Electron-Deficient Alkenes via Radical Coupling at Room Temperature

A new, simple, and metal-free route for the diselenation of maleimides has been first developed employing (bis(trifluoroacetoxy)iodo)benzene (PIFA) at room temperature. The present method is compatible with different functional groups, and various diselenyl maleimides were obtained in moderate to excellent yields. Moreover, this protocol further highlights the unique practical application for the functionalization of biologically relevant molecules and amino acid derivatives. Preliminary mechanism studies suggest that radicals may be involved in this novel transformation. Additionally, this protocol is also applicable for the monoselenation of maleimides by switching the reaction conditions and selenation of other electron-deficient alkenes.

Synthesis of fluoroolefin derivatives by nickel(II)-catalyzed trifluorovinylation and 1,2,2-trifluoroethylation of cinnamyl alcohols

Nickel(II)-catalyzed regioselective trifluorovinylation and 1,2,2-trifluoroethylation of allyl alcohols with trifluorovinyl reagents were performed. The reaction of (E)-3-phenylprop-2-en-1-ol and trifluorovinylzinc bromide (TFVZ) afforded 1,2,2-trifluorovinyl diene in moderate to high yields. The reaction of (E)-3-phenylprop-2-en-1-ol and trifluorovinyl trimethylsilane (TFVTMS) resulted in the novel nucleophilic addition product 1,1,2-trifluoroethoxy aryl olefin.

Functionalized quinoxalinones as privileged structures with broad-ranging pharmacological activities

Quinoxalinones are a class of heterocyclic compounds which attract extensive attention owing to their potential in the field of organic synthesis and medicinal chemistry. During the past few decades, many new synthetic strategies toward the functionalization of quinoxalinone based scaffolds have been witnessed. Regrettably, there are only a few reports on the pharmacological activities of quinoxalinone scaffolds from a medicinal chemistry perspective. Therefore, herein we intend to outline the applications of multifunctional quinoxalinones as privileged structures possessing various biological activities, including anticancer, neuroprotective, antibacterial, antiviral, antiparasitic, anti-inflammatory, antiallergic, anti-cardiovascular, anti-diabetes, antioxidation, etc. We hope that this review will facilitate the development of quinoxalinone derivatives in medicinal chemistry.

Rh-Catalyzed Oxidation and Trifluoroethoxylation of N-Aryl-pyrrolidin-2-ones : A Domino Approach for the Synthesis of N-Aryl-5-(2,2,2-trifluoroethoxy)-1,5- dihydro-2H-pyrrol-2-ones

The synthesis of trifluoroethoxylated dihydropyrrolidones via rhodium-catalyzed oxidation and trifluoroethoxylation of pyrrolidones is presented in this paper. This process realized trifluoroethoxylation of non-activated sp3 C-H by domino approach for the...

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...

Decatungstate-Photocatalyzed Direct Coupling of Inert Alkanes and Quinoxalin-2(1H)-ones with H2 Evolution

A tetrabutylammonium decatungstate (TBADT)-photocatalyzed direct coupling of inert alkanes and quinoxalin-2(1H)-ones with H2 evolution was developed at room temperature. The present transformation achieved the direct C(sp3)-H/C(sp2)-H coupling under noble metal-free,...

Bromine-radical-induced Csp2–H difluoroalkylation of quinoxalinones and hydrazones through visible-light-promoted Csp3–Br bond homolysis

Bromine radicals derived from photo-induced Csp3–Br bond homolysis can mediate H abstraction/imine radical formation from quinoxalinones and hydrazones, which in turn quench the in situ-generated difluoroalkyl radicals to furnish the products.

Metal-free three-component cyanoalkylation of quinoxalin-2(1H)-ones with vinylarenes and azobis(alkylcarbonitrile)s

A K2S2O8-mediated C3 cyanoalkylation of quinoxalin-2(1H)-ones via a three-component radical cascade reaction with vinylarenes and azobis(alkylcarbonitrile)s has been achieved.

Copper-catalyzed selective oxidation of hydrazones through C(sp3)-H functionalization

A simple and mild protocol for copper-catalyzed oxidation of hydrazones at the α-position has been reported. Various substrates are compatible, providing the corresponding products in moderate to good yields. This strategy provides an efficient and convenient solution for the synthesis of carbonyl hydrazone. A free radical pathway mechanism is suggested for the transformation.

Hypervalent Iodine(III)-Promoted Radical Oxidative C-H Annulation of Arylamines with α-Keto Acids

A novel catalyst-free radical oxidative C-H annulation reaction of arylamines with α-keto acids toward benzoxazin-2-ones synthesis under mild conditions was developed. This hypervalent iodine(III)-promoted process eliminated the use of a metal catalyst or additive with high levels of functional group tolerance. Hypervalent iodine(III) was both an oxidant and a radical initiator for this reaction. The synthetic utility of this method was confirmed by the synthesis of the natural product cephalandole A.

Visible-Light-Induced C(sp2)-C(sp3) Cross-Dehydrogenative-Coupling Reaction of N-Heterocycles with N-Alkyl-N-methylanilines under Mild Conditions

Disclosed herein is a cross-dehydrogenative-coupling reaction of N-heterocycles including 1,2,4-triazine-3,5(2H, 4H)-diones and quinoxaline-2(1H)-ones with N-methylanilines to form C(sp²)-C(sp³) under visible-light illumination and ambient air at room temperature. In this process, easily available Ru(bpy)₃Cl₂·6H₂O serves as the catalyst, and air acts as the green oxidant. This method features high atom economy, environmental friendliness, and convenient operation and provides an efficient and practical access to aminomethyl-substituted N-heterocycles with extensive functional group compatibility in 40-86% yields.

Transient directing group controlled regiodivergent C(sp3)–H and C(sp2)–H polyfluoroalkoxylation of aromatic aldehydes

A novel method for achieving regiodivergent C(sp3)–H and C(sp2)–H polyfluoroalkoxylation in the o-methyl benzaldehyde framework by altering the transient directing group is disclosed.

Rh(iii)-Catalyzed Csp2–Csp3 bond alkoxylation of α-indolyl alcohols via C–C σ bond cleavage

A Rh(iii)-catalyzed direct Csp²–Csp³ bond alkoxylation of α-(2-indolyl)alcohols with alcohols has been achieved via C–C sigma bond/C–O single bond switch.

Photocatalytic intramolecular radical cyclization involved synergistic SET and HAT: synthesis of 3,3-difluoro-γ-lactams

A mild and metal-free protocol for visible-light induced intramolecular radical cyclization of N-allyl(propargyl)-2-bromo-2,2-difluoro-N-arylacetamide has been developed.