Ruthenium(II)-Catalyzed C–C/C–N Coupling of 2-Arylquinazolinones with Vinylene Carbonate: Access to Fused Quinazolinones

Iodine-promoted sequential C(sp3)-H oxidation and cyclization of aryl methyl ketones with 2-(2-aminophenyl)quinazolin-4(3H)-ones

An I2-promoted, metal-free protocol has been developed for the one-pot synthesis of 6-aroyl-5,6-dihydro-8H-quinazolino[4,3-b]quinazolin-8-ones from readily accessible substrates. This reaction involves the in situ sp3 C-H oxidation of aryl methyl ketones to phenylglyoxal, followed by imine formation and intramolecular nucleophilic addition, resulting in the formation of two new C-N bonds. Furthermore, the method is applicable to a wide range of aryl methyl ketones, including heterocycles and drug-derived substrates, yielding the desired products with yields ranging from 62% to 93%. Additionally, the practical utility of this approach was demonstrated through gram-scale synthesis.

Visible-light promoted radical cascade cyclization of 3-allyl-2-arylquinazolinones for the synthesis of phosphorylated dihydroisoquinolino[1,2-b]quinazolinones

A novel visible-light promoted metal-free radical cascade cyclization reaction has been developed with 3-allyl-2-arylquinazolinones as a new class of radical acceptor. This photocatalytic protocol represents an efficient approach to construct phosphorylated dihydroisoquinolino[1,2-b]quinazolinones featuring mild conditions, broad substrate scope, and gram-scale synthesis.

"One pot" synthesis of quinazolinone-[2,3]-fused polycyclic scaffolds in a three-step reaction sequence

Diverse quinazolinone-[2,3]-fused polycyclic skeletons occupy a prominent position in drug discovery. Even with currently available methods there still remain unmet needs for flexible access to such structures. Herein, we have explored a mild "one pot" procedure for the construction of various quinazolinone-[2,3]-fused polycycles. The procedure involves Pd-catalyzed carbonylation of N-(2-iodophenyl)acetamides, release of the masked terminal amine, and two sequential and spontaneous cyclizations. This generally applicable approach features easy assembly of precursors from readily available starting materials, mild reaction conditions, non-cumbersome operation, and polycyclic diversity.

Visible-light-induced three-component reactions of α-diazoesters, quinazolinones and cyclic ethers toward quinazoline-based hybrids

An effective approach for the construction of 4-short-chain ether attached carbonyl group-substituted quinazolines was developed. Visible-light-induced three-component reactions of α-diazoesters, quinazolinones, and cyclic ethers, with a broad substrate scope and excellent functional group tolerance, under extremely mild conditions without the need for any additional additives and catalysts, selectively led to quinazoline-based hybrids in good to excellent yields. The synthesized hybrids, which are a conglomeration of a quinazoline, a short-chain ether, and a carbonyl group in one molecular skeleton, have potential for application in the development of new drugs or drug candidates.

Palladium-catalyzed denitrogenation/vinylation of benzotriazinones with vinylene carbonate

Herein, a novel Pd-catalyzed denitrogenation/vinylation of benzotriazinones using vinylene carbonate as the vinylation reagent is reported. This transformation demonstrates an unprecedented skeletal editing approach, effectively converting NN to CC fragments in situ and synthesizing a collection of isoquinolinones with broad-spectrum functional group tolerance. Moreover, the quite concise reaction system and late-stage modification of bioactive molecules comprehensively underscore the practical potential of this protocol.

(NH4)2S2O8 promoted tandem radical cyclization of quinazolin-4(3H)-ones with oxamic acids for the construction of fused quinazolinones under metal-free conditions

A novel cascade radical addition/cyclization reaction of non-activated olefins and oxamic acids has been proposed. Under transition metal-free conditions, 36 quinazolinone derivatives containing an amide moiety were successfully synthesized, with the highest yield being 81%. This method involves the preparation of aminoacyl fused quinazolinone derivatives under mild conditions, offering advantages such as a high yield, a broad substrate compatibility, and a high atom economy.

Carboxylic Acid-Enabled Vinylene Transfer Reaction by Co(III) Catalyst: Scope and Applications to the Five-Step Total Synthesis of Protoberberine Alkaloids Containing Free Hydroxyl Group without Protection

A Co(III)-catalyzed vinylene transfer reaction enabled by carboxylic acid is presented. This redox-neutral transformation tolerates various functional groups, including free hydroxyl groups, and features practicality. Five-step routes based on the vinylene transfer reaction and Heck annulation have been devised to the total synthesis of 8-oxodehydrodiscretamine and 2-demethyl-oxypalmatine without the protection of the free hydroxyl functionality.

Persulfate-Promoted Carbamoylation/Cyclization of Alkenes: Synthesis of Amide-Containing Quinazolinones

The incorporation of amide groups into biologically active molecules has been proven to be an efficient strategy for drug design and discovery. In this study, we present a simple and practical method for the synthesis of amide-containing quinazolin-4(3H)-ones under transition-metal-free conditions. This is achieved through a carbamoyl-radical-triggered cascade cyclization of N3-alkenyl-tethered quinazolinones. Notably, the carbamoyl radical is generated in situ from the oxidative decarboxylative process of oxamic acids in the presence of (NH4)2S2O8.

Synthesis of Fluoren-9-ones via Pd-Catalyzed Annulation of 2-Iodobiphenyls with Vinylene Carbonate

A palladium-catalyzed reaction for intermolecular selective C-H cyclocarbonylation of 2-iodobiphenyls is described. Intriguingly, the vinylene carbonate acts as a carbon monoxide transfer agent to enable the annulation reaction. Moreover, as a versatile synthon, fluoren-9-one can be transformed into a variety of functionalized organic molecules, such as [1,1'-biphenyl]-2-carboxylic acid, 1'H,3'H-spiro[fluorene-9,2'-perimidine] and N-tosylhydrazones.

Rhodium-catalyzed divergent dehydroxylation/alkenylation of hydroxyisoindolinones with vinylene carbonate

Herein, a novel organic transformation involving rhodium-catalyzed divergent dehydroxylation/alkenylation of hydroxyisoindolinone with vinylene carbonate is reported, and a series of architecturally rigid and widely used spirolactams are obtained with excellent functional group tolerance and high selectivity. Remarkably, the promising vinylene carbonate reagent presents a distinct chemical reactivity as a vinyl-oxygen cyclic synthon and first transfers the C-H bond to spiroheterocycle scaffolds. Moreover, another chemoselectivity, direct dehydrogenative coupling with vinylene carbonate, is also presented. This protocol is compatible with green chemistry and only releases H2O and CO2 as byproducts.

Rhodium(III)-Catalyzed C-H/N-H Activation for Direct Synthesis of Pyrimidoindolones under Mild Conditions

Pyrimidoindolones are an important structural motif found in many natural products and are essential to the pharmaceutical and agrochemical industry. Direct synthesis of 3,4-unsubstituted pyrimidoindolones is not easily accessible. Here we report a rhodium(III)-catalyzed C-H/N-H activation and annulation approach for obtaining pyrimidoindolones from N-carbamoylindoles and vinylene carbonate. The reaction occurs at room temperature and does not require any external oxidants. A diverse spectrum of indoles were demonstrated to be viable substrates capable of producing the desired pyrimidoindolones in high yields. In addition, the reaction scope has been expanded to include pyrrole substrate. Furthermore, detailed mechanistic studies have been performed to delineate the working mode of the reaction.

Synthesis of 2,3-Fused Quinazolinones via the Radical Cascade Pathway and Reaction Mechanistic Studies by DFT Calculations

An efficient radical cascade cyclization of unactivated alkenes toward the synthesis of a series of ring-fused quinazolinones has been developed in moderate to excellent yields using commercially available ethers, alkanes, and alcohols, respectively, under a base-free condition in a short time without a transition metal as catalyst. Notably, the transformations can be carried out with the advantages of a broad substrate scope and high atomic economy. Density functional theory calculations and wavefunction analyses were performed to elucidate the radical reaction mechanism.

An Aldehyde-Driven, Fe(0)-Mediated, One-Pot Reductive Cyclization: Direct Access to 5,6-Dihydro-quinazolino[4,3-b]quinazolin-8-ones and Photophysical Study

A short, proficient, and regioselective synthesis of biheterocyclic 5,6-dihydro-quinazolino[4,3-b]quinazolin-8-ones has been revealed via an Fe(0)-powder-mediated, one-pot reductive cyclization protocol. Mechanistic investigation proved that water acts as a source of hydrogen for the reduction of the nitro group and the reaction rate was accelerated by an aldehyde. The designed transformation works under aerobic conditions, providing a series of bio-inspired molecular scaffolds. In addition, the photophysical study showed blue fluorescence emission with a good fluorescence quantum yield.

t-BuOK-Catalyzed Regio- and Stereoselective Intramolecular Hydroamination Reaction Leading to Phthalazinoquinazolinone Derivatives

We report herein an efficient and practical strategy for the preparation of 5H-phthalazino[1,2-b]quinazolin-8(6H)-one derivatives through a t-BuOK-catalyzed intramolecular hydroamination reaction of functionalized quinazolinones under extremely mild reaction conditions. A variety of quinazolinone substrates are well tolerated to furnish the corresponding products in good to high yields via an exclusive 6-exo-dig cyclization process. The present protocol has the advantages of readily obtainable starting materials, broad substrate scope, and high regio- and stereoselectivity.

Tandem C-C/C-N Bond Formation via Rh(III)-Catalyzed α-Fluoroalkenylation and Sequential Annulation of 2-Arylquinazolinones and gem-Difluorostyrenes

An efficient method of Rh(III)-catalyzed coupling reaction between 2-arylquinazolinones and gem-difluorostyrenes has been developed. In this work, two diverse structures of monofluoroalkenes and isoindolo[1,2-b]quinazolin-10(12H)-one derivatives were respectively synthesized by controlling the amount of additives (Ca(OH)₂ and AgNTf₂) to achieve controlled stepwise breaking of the C-F bonds of gem-difluorostyrenes. This reaction has the characteristics of a wide range of substrates and good functional group tolerance. Meanwhile, several control experiments were conducted and a plausible mechanism was proposed.

Transition metal-free annulative vinylene transfer via the 1,3-dipolar reaction of N-ylides: access to benzo-fused indolizines

An efficient metal-free annulative vinylene transfer protocol for the synthesis of benzo-fused indolizines via 1,3-dipolar cycloadditions of N-ylides with vinylene carbonate has been developed. Vinylene carbonate serves as an acetylene surrogate without any external oxidant involved. This transformation leads to the direct construction of versatile benzo-fused indolizine derivatives in moderate to good yields.

Ru(II)-Catalyzed Regioselective C(5)-H Functionalization of Quinazolinone-Coumarin Conjugates: Synthesis and Photophysical Studies

The quinazolinone template offers an exciting potential for transforming molecules into useful bioactivity. Herein, we report the first regioselective C-5 alkenylation of quinazolinone-coumarin conjugates via ruthenium(II) catalyst using amide as a weak directing group. This methodology permits excellent regioselectivity, extensive substrate tolerance, and mild reaction conditions. In addition, it generates interesting fluorophores that show positive solvatochromism in the range from 404 nm (toluene) to 541 nm (methanol).

Ruthenium-catalyzed oxidative coupling of vinylene carbonate with isoxazoles: access to fused anthranils

A ruthenium-catalyzed oxidative coupling of vinylene carbonate with isoxazoles has been developed to achieve the direct C-H formylmethylation of a diverse array of arylisoxazoles utilizing the isoxazole ring as the directing group. A simple manipulation of the established reaction conditions leads to the formation of fused-anthranils. Importantly, the vinylene carbonate functions as both a formylmethyl cation equivalent through a decarboxylation process and an acetylene equivalent. Control experiments were conducted to elucidate a plausible mechanism. This methodology is expected to provide a facile and expeditious approach for the synthesis of formylmethyl isoxazoles and fused-anthranils.

Rh(III)-Catalyzed Synthesis of Indazolo[2,3-a]quinolines: Vinylene Carbonate as C1 and C2 Building Blocks

A rhodium-catalyzed cyclization of azobenzenes and vinylene carbonate via C-H bond activation to construct indazolo[2,3-a]quinolines has been developed. This protocol offers an efficient method for synthesis of the titled products in good yields with broad functional group tolerance. In this reaction, three C-C bonds and C-N bond are formed in one pot, and vinylene carbonate (VC) acts as C1 and C2 synthons as well as "vinylene transfer" agent and acylation reagent in the construction of target-fused heterocycles. Moreover, the products exhibit favorable fluorescence properties, which indicate their potential application as fluorescent materials and biosensors.

Recent Advances on the Synthesis of 2,3-Fused Quinazolinones

As one of the most important structural units in pharmaceuticals and medicinal chemistry, quinazolinone and its derivatives exhibit a wide range of biological and pharmacological activities, including anti-inflammatory, antitubercular, antiviral,...

Transition metal- and oxidant-free [3 + 2] cyclization of azomethine imines utilizing vinylene carbonate as dual synthons

A transition metal- and oxidant-free C–C/C–N annulation of azomethine imines with vinylene carbonate as dual synthons under simple reaction conditions is described herein.

Manganese-Catalyzed [4 + 2] Annulation of N-H Amidines with Vinylene Carbonate via C-H Activation

Manganese-catalyzed C-H bond functionalization of aryl amidines for the synthesis of 1-aminoisoquinolines in the presence of vinylene carbonate has been developed. The reaction features a broad substrate scope and proceeds under mild reaction conditions with only the carbonate anion as the byproduct.

N,N-Dimethylformamide as Carbon Synthons for the Synthesis of N-Heterocycles: Pyrrolo/Indolo[1,2-a]quinoxalines and Quinazolin-4-ones

N,N-dimethylformamide (DMF) as synthetic precursors contributing especially the methyl, acyl, and amino groups has played a significant role in heterocycle syntheses and functionalization. In this protocol, a wide range of pyrrolo/indolo[1,2-a]quinoxalines and quinazolin-4-ones were obtained in moderate to good yields by using elemental iodine without any metal or peroxides. We considered that N-methyl and N-acyl of DMF participate and complete the reaction separately through different mechanisms, which displayed potential still to be explored of DMF.

Rhodium-Catalyzed C-H Annulation of Free Anilines with Vinylene Carbonate as a Bifunctional Synthon

Chemical transformation with vinylene carbonate as an emerging synthetic unit has recently attracted considerable attention. This report is a novel conversion pattern with vinylene carbonate, in which such a vibrant reagent unprecedentedly acts as a difunctional coupling partner to complete the C-H annulation of free anilines. From commercially available substrates, this protocol leads to the rapid construction of synthetically versatile 2-methylquinoline derivatives (43 examples) with excellent functionality tolerance.

Synthesis of oxazolidinones through ring-opening and annulation of vinylene carbonate with 2-pyrrolyl/indolylanilines under Rh(III) catalysis

Herein, we have developed a rhodium-catalyzed C-H functionalization and subsequent intramolecular ring-opening/cyclization of vinylene carbonate with 2-pyrrolyl/indolylanilines, which leads to oxazolidinones in moderate to good yields. In this transformation, vinylene carbonate only eliminates one oxygen atom rather than -CO₃ or CO₂. Furthermore, some control experiments are conducted to elucidate the reaction mechanism.

Rhodium-Catalyzed Dehydrogenative Annulation of N-Arylmethanimines with Vinylene Carbonate for Synthesizing Quinolines

Here we report a novel Rh-catalyzed C-H/C-H alkenylation of N-arylmethanimines with vinylene carbonate acting as a vinylene unit. Forty examples of C3,C4-nonsubstituted quinolines were achieved from commercially available starting materials. This identified process features an exceedingly simple system, a lower loading of catalyst, and the capacity for postfunctionalization with bioactive molecules.

Ru(II)-Catalyzed C–H Activation Reaction between 2-Phenyl­quinazolinone and Vinylene Carbonate

In the report, we described the ruthenium(II)-catalyzed C–H activation/cyclization of 2-arylquinazolinones with vinyl carbonate for the synthesis of different fused quinazolinones. Through this strategy, the 6-hydroxy-5,6-dihydro-8H-isoquinolino[1,2-b]quinazolin-8-one and 8H-isoquino[1,2-b] quinazolin-8-one have been obtained, respectively, under different temperatures. Additionally, the reaction features broad substrate scope and good yields, only producing carbon dioxide as byproduct. Moreover, we performed preliminary mechanistic studies of this reaction and proposed a possible mechanism.

Mn(III)-Mediated Radical Cyclization of o-Alkenyl Aromatic Isocyanides with Boronic Acids: Access to N-Unprotected 2-Aryl-3-cyanoindoles

The synthesis of N-unprotected 2-aryl-3-cyanoindoles was realized via the Mn(III)-mediated radical cascade cyclization of o-alkenyl aromatic isocyanides with boronic acids. A possible mechanism involving a sequential intermolecular radical addition, intramolecular cyclization, and cleavage of the C-C bond under mild reaction conditions is proposed. Mechanism studies show that H₂O or O₂ might provide the oxygen source for the elimination of benzaldehyde.

Rhodium-catalysed direct formylmethylation using vinylene carbonate and sequential dehydrogenative esterification

A rhodium-catalysed direct formylmethylation adopting vinylene carbonate as an ethynol equivalent is reported. The developed catalytic system is further utilised for the oxidant-free production of esters with the liberation of hydrogen gas. Some control experiments are conducted to elucidate the reaction mechanism.

Synthesis of (2H)-Indazoles and Dihydrocinnolinones through Annulation of Azobenzenes with Vinylene Carbonate under Rh(III) Catalysis

The Rh(III)-catalyzed C-H functionalization and subsequent intramolecular cyclization between azobenzenes and vinylene carbonate is described herein. Depending on the electronic property of azobenzenes, this transformation results in the formation of (2H)-indazoles or dihydrocinnolin-4-ones through the generation of ortho-alkylated azo-intermediates followed by decarboxylation. Surprisingly, vinylene carbonate acts as an acetaldehyde or acetyl surrogate to enable the [4 + 1] or [4 + 2] annulation reaction. This transformation is characterized by its mild reaction conditions, simplicity, and excellent functional group compatibility.