Recent advances in the transition-metal-free synthesis of quinoxalines

Adamantane-Quinoxalone Hybrids: Precision Chemotypes and Their Molecular Mechanisms in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive blood cancer with a poor prognosis, especially when diagnosed late. Around 10-15% of cases involve the specific chromosomal abnormality t(8;21), which drives uncontrolled myeloid cell proliferation and contributes to disease onset. Despite advances in AML research and treatment protocols, outcomes for t(8;21) AML remain stagnant, as patients receive standard, nonspecific chemotherapies. This one-size-fits-all approach targets both cancerous and healthy cells, leading to unwanted toxicity and highlighting the urgent need for targeted therapies. In this study, we present a precision chemotype based on a quinoxalone-tethered adamantane framework developed via a metal- and light-free protocol. The compound selectively inhibits t(8;21) AML cell proliferation and induces cell death by disrupting growth and metabolic pathways, as demonstrated through bioassays, RNA sequencing, and proteomic analysis. Notably, it spares other leukemic and solid cancer cells, underscoring its specificity and potential as a targeted therapy for t(8;21) AML.

Transition-metal-free regioselective synthesis of spiro-oxazolidines through [3 + 2] annulation reactions of azadienes with haloalcohols

The transition-metal-free regioselective [3 + 2] annulation of azadienes with haloalcohols for the preparation of highly functionalized spiro-oxazolidines is experimentally simple and proceeds under mild conditions. The metal-free protocols have more significance than the metal-catalyzed ones when the toxicity associated with the metal catalyst is considered. This transformation features a broad substrate scope, good yields, and excellent regioselectivity. Moreover, large-scale synthesis and representative transformations of spiro-oxazolidines were carried out to provide additional evidence on the practicality of this approach.

Efficient Microwave Irradiation-Assisted Synthesis of Benzodioxinoquinoxaline and Its Donor-Variegated Derivatives Enabling Long-Lived Emission and Efficient Bipolar Charge Carrier Transport

To enhance the usually low-charge carrier mobilities of highly twisted donor-acceptor-type compounds that exhibit thermally activated delayed fluorescence, we designed a rodlike acceptor benzodioxinoquinoxaline. This acceptor and two donor-acceptor-donor derivatives were synthesized via microwave Buchwald-Hartwig cross-coupling reactions with yields of up to 91%. The compounds exhibit three different types of photoluminescence, which is well-explained by quantum chemical calculations. Benzodioxinoquinoxaline shows blue fluorescence, with a very short lifetime of 0.64 ns. Its derivatives exhibit either green solid-state-enhanced thermally activated delayed fluorescence (SSE-TADF) or room-temperature phosphorescence (RTP) with lifetimes approaching 7 ms. When molecularly dispersed in a polymeric host, the compounds show a photoluminescence quantum yield close to 60%. The derivatives containing acridine or phenoxazine moieties exhibit bipolar charge transport. At an electric field of 5.8 × 105 V/cm, hole and electron mobilities of the phenoxazine-containing compound reach 3.2 × 10-4 and 1.5 × 10-4 cm2 V-1 s-1, respectively. Among the studied SSE-TADF-based organic light-emitting diodes, the device containing this compound shows the highest external quantum efficiency of 12.3% due to the good charge-transporting and SSE-TADF parameters of the emitter.

Photoredox-Catalyzed Cross-Coupling of In Situ Generated Quinoxalinones with Indoles for the Synthesis of Tertiary Alcohols

A visible light-driven photoredox-catalyzed direct C(sp2)-H functionalization of N-H free indoles with quinoxalinones generated in situ from 2,2-dihydroxy-1H-indene-1,3(2H)-dione and phenylene-1,2-diamines has been reported with the aid of Na2-Eosin Y as the photocatalyst and the Hünig base as the sacrificial electron and proton donor. The reaction provides easy access to a variety of quaternary-centered C-3 selective indole-substituted tertiary alcohols in good yields. Mechanistic studies demonstrated the realization of photoredox-catalyzed in situ quinoxalinone formation and their proton-coupled single electron reduction to the corresponding ketyl radicals followed by cross-coupling with indoles. The potential applications of the synthesized tertiary alcohols in photoacid-catalyzed carbon-carbon and carbon-sulfur bond-forming reactions feature the key findings of the present work.

A 1,2-Aryl Migration Reaction in Visible-Light-Mediated Synthesis of Quinoxaline Derivatives: Mechanistic Studies

The synthesis of quinoxaline derivatives holds critical importance in various fields ranging from pharmaceuticals to material science. In this study, we introduce a practical light-mediated method for the efficient synthesis of quinoxaline derivatives. This approach enabled the sequential two-step, one-pot synthesis of 1,2-dihydro-2,2-diaryl-substituted quinoxalines from quinones, alkynes, and diamines. By adjusting the stoichiometric ratios and reaction conditions, the method was shifted to yield 2,3-diaryl-substituted quinoxalines exclusively, demonstrating remarkable versatility and efficiency. This switch in reaction outcomes was revealed to involve an oxidative 1,2-aryl migration through a combination of thorough experimental and computational mechanistic studies.

Highly enantioselective synthesis of both enantiomers of tetrahydroquinoxaline derivatives via Ir-catalyzed asymmetric hydrogenation

A novel Ir-catalyzed asymmetric hydrogenation protocol for the synthesis of chiral tetrahydroquinoxaline (THQ) derivatives has been developed. By simply adjusting the reaction solvent, both enantiomers of mono-substituted chiral THQs could be selectively obtained in high yields with excellent enantioselectivities (toluene/dioxane: up to 93% yield and 98% ee (R); EtOH: up to 83% yield and 93% ee (S)). For 2,3-disubstituted chiral THQs, the cis-hydrogenation products were obtained with up to 95% yield, 20 : 1 dr, and 94% ee. Remarkably, this methodology was also applicable under continuous flow conditions, yielding gram-scale products with comparable yields and enantioselectivities (dioxane: 91% yield and 93% ee (R); EtOH: 90% yield and 87% ee (S)). Unlike previously reported Ir-catalyzed asymmetric hydrogenation protocols, this system exhibited a significant improvement as it required no additional additives. Furthermore, comprehensive mechanistic studies including deuterium-labeling experiments, control experiments, kinetic studies, and density functional theory (DFT) calculations were conducted to reveal the underlying mechanism of enantioselectivities for both enantiomers.

Design, Synthesis, Antifungal Activity, and 3D-QSAR Study of Novel Quinoxaline-2-Oxyacetate Hydrazide

Plant pathogenic fungi pose a major threat to global food security, ecosystem services, and human livelihoods. Effective and broad-spectrum fungicides are needed to combat these pathogens. In this study, a novel antifungal 2-oxyacetate hydrazide quinoxaline scaffold as a simple analogue was designed and synthesized. Their antifungal activities were evaluated against Botrytis cinerea (B. cinerea), Altemaria solani (A. solani), Gibberella zeae (G. zeae), Rhizoctonia solani (R. solani), Colletotrichum orbiculare (C. orbiculare), and Alternaria alternata (A. alternata). These results demonstrated that most compounds exhibited remarkable inhibitory activities and possessed better efficacy than ridylbacterin, such as compound 15 (EC50 = 0.87 μg/mL against G. zeae, EC50 = 1.01 μg/mL against C. orbiculare) and compound 1 (EC50 = 1.54 μg/mL against A. alternata, EC50 = 0.20 μg/mL against R. solani). The 3D-QSAR analysis of quinoxaline-2-oxyacetate hydrazide derivatives has provided new insights into the design and optimization of novel antifungal drug molecules based on quinoxaline.

Sodium sulfide-promoted regiodefined redox condensation of o-nitroanilines with aryl ketones to benzo[a]phenazines and quinoxalines

Inexpensive sodium sulfide trihydrate was found to promote unprecedented 6e-regio-predefined redox condensation of o-nitroanilines with α-tetralones to benzo[a]phenazines. The method was also successfully extended to acetophenones and higher homologs as reducing partners to provide 2-phenylquinoxalines. Compared to traditional approaches toward benzo[a]phenazine and quinoxaline cores starting with o-phenylenediamines, the present strategy could afford these heterocycles with well-defined regiochemistry based on the structure of starting o-nitroanilines.

Metal-Free Highly Regioselective 1,4-Sulfonyliodination of 1,3-Enynes

Herein, a novel, practical, and green synthetic method using readily available 1,3-enynes with sulfonyl hydrazides and I₂ through tert-butyl hydroperoxide (TBHP)-mediated 1,4-sulfonyliodination has been developed for synthesizing various tetrasubstituted allenyl iodides under metal-free conditions. Notably, the proposed method exhibits a broad substrate scope, operational simplicity, tolerance to air, high functional-group tolerance, satisfactory yields, and excellent regioselectivity as well as involves the use of cost-effective reagents such as green oxidants.

Visible-light-induced organophotocatalytic and singlet oxygen-initiated domino construction of 1,4-dihydropyridines, C-3 functionalized spiro[indoline-3,4'-pyridines] and C-11 functionalized spiro[indeno-[1,2-b]quinoxaline-11,4'-pyridines]

A highly efficient pot, atom, and step economical method for the construction of pharmacologically potent structurally functionalized 1,4-dihydropyridines, quaternary centered C-3 functionalized spiro[indoline-3,4'-pyridines], and C-11 functionalized spiro[indeno[1,2-b]quinoxaline-11,4'-pyridines] via rose bengal photoredox catalysis under blue LED irradiation in an aqueous medium at room temperature has been developed. The products were isolated in excellent yields within a short reaction time for a variety of functional groups under transition metal- and ligand-free energy-efficient conditions in a green solvent system with high reaction mass efficiency and process mass intensity, which are the key advantages of the current work.

Brønsted acid catalyzed mechanochemical domino multicomponent reactions by employing liquid assisted grindstone chemistry

Here, we have demonstrated a metal-free energy-efficient mechanochemical approach for expedient access to a diverse set of 2-amino-3-cyano-aryl/heteroaryl-4H-chromenes, tetrahydrospiro[chromene-3,4'-indoline], 2,2'-aryl/heteroarylmethylene-bis(3-hydroxy-5,5-dimethylcyclohex-2-enone) as well as tetrahydro-1H-xanthen-1-one by employing the reactivity of 5,5-dimethylcyclohexane-1,3-dione/cyclohexane-1,3-dione with TsOH⋅H₂O as Brønsted acid catalyst under water-assisted grinding conditions at ambient temperature. The ability to accomplish multiple C-C, C=C, C-O, and C-N bonds from readily available starting materials via a domino multicomponent strategy in the absence of metal-catalyst as well as volatile organic solvents with an immediate reduction in the cost of the transformation without necessitates complex operational procedures, features the significant highlights of this approach. The excellent yield of the products, broad functional group tolerances, easy set-up, column-free, scalable synthesis with ultralow catalyst loading, short reaction time, waste-free, ligand-free, and toxic-free, are other notable advantages of this approach. The greenness and sustainability of the protocol were also established by demonstrating several green metrics parameters.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Recent advances and prospects in the organocatalytic synthesis of quinazolinones

Quinazolinone, a bicyclic compound, comprises a pyrimidine ring fused at 4´ and 8´ positions with a benzene ring and constitutes a substantial class of nitrogen-containing heterocyclic compounds on account of their frequent existence in the key fragments of many natural alkaloids and pharmaceutically active components. Consequently, tremendous efforts have been subjected to the elegant construction of these compounds and have recently received immense interest in synthetic and medicinal chemistry. The domain of synthetic organic chemistry has grown significantly over the past few decades for the construction of highly functionalized therapeutically potential complex molecular structures with the aid of small organic molecules by replacing transition-metal catalysis. The rapid access to this heterocycle by means of organocatalytic strategy has provided new alternatives from the viewpoint of synthetic and green chemistry. In this review article, we have demonstrated a clear presentation of the recent organocatalytic synthesis of quinazolinones of potential therapeutic interests and covered the literature from 2015 to date. In addition to these, a clear presentation and understanding of the mechanistic aspects, features, and limitations of the developed reaction methodologies have been highlighted.

Ultrasound-assisted transition-metal-free catalysis: a sustainable route towards the synthesis of bioactive heterocycles

Heterocycles of synthetic and natural origin are a well-established class of compounds representing a broad range of organic molecules that constitute over 60% of drugs and agrochemicals in the market or research pipeline. Considering the vast abundance of these structural motifs, the development of chemical processes providing easy access to novel complex target molecules by introducing environmentally benign conditions with the main focus on improving the cost-effectiveness of the chemical transformation is highly demanding and challenging. Accordingly, sonochemistry appears to be an excellent alternative and a highly feasible environmentally benign energy input that has recently received considerable and steadily increasing interest in organic synthesis. However, the involvement of transition-metal-catalyst(s) in a chemical process often triggers an unintended impact on the greenness or sustainability of the transformation. Consequently, enormous efforts have been devoted to developing metal-free routes for assembling various heterocycles of medicinal interest, particularly under ultrasound irradiation. The present review article aims to demonstrate a brief overview of the current progress accomplished in the ultrasound-assisted synthesis of pharmaceutically relevant diverse heterocycles using transition-metal-free catalysis.

Sonochemistry in an organocatalytic domino reaction: an expedient multicomponent access to structurally functionalized dihydropyrano[3,2-b]pyrans, spiro-pyrano[3,2-b]pyrans, and spiro-indenoquinoxaline-pyranopyrans under ambient conditions

A highly convenient and sustainable one-pot approach for the diversely-oriented synthesis of a variety of medicinally privileged amino-substituted 4,8-dihydropyrano[3,2-b]pyran-3-carbonitriles, and spiro[indoline-3,4'-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylate derivatives on the basis of a domino three-component reaction of readily available carbonyl compounds including aryl aldehydes or isatins, active methylene compounds, and kojic acid as a Michael donor using secondary amine catalyst l-proline under ultrasound irradiation in aqueous ethanolic solution at ambient temperature has been developed. This methodology can involve the assembly of C-C, C[double bond, length as m-dash]C, C-O, C-N bonds via a one-pot operation, and following this protocol, a series of novel amino-substituted spiro[indeno[1,2-b]quinoxaline-11,4-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylates have been synthesized. The practical utility of this method was found to be very efficient for scale-up reaction and other useful transformations. The methodology provides significant advantages including mild reaction conditions, energy-efficiency, short reaction time, fast reaction, simple work-up procedure, broad functional group tolerances, utilization of reusable catalyst, green solvent system, being metal-free, ligand-free, waste-free, inexpensive, etc. Excellent chemical yields have been achieved without using column chromatography. To address the issues of green and more sustainable chemistry, several metrics including Atom Economy (AE), Reaction Mass Efficiency (RME), Atom efficiency, E-factor, Process Mass Intensity (PMI), and Carbon Efficiency (CE) have been quantified for the present methodology that indicates the greenness of the present protocol.