Copper-Catalyzed Annulation or Homocoupling of Sulfoxonium Ylides: Synthesis of 2,3-Diaroylquinolines or α,α,β-Tricarbonyl Sulfoxonium Ylides

Isocyanide-Based Multicomponent Reaction: Cascade α-Acyloxylation/Carboxamidation and [3 + 1+1] Cyclization of I(III)/S(VI)-Ylides

A metal-free cascade of α-acyloxylation/carboxamidation of I(III)/S(VI)-ylides, carboxylic acids, and isonitriles via a Passerini-like multicomponent reaction is reported. Unexpectedly, [3 + 1+1] cyclization involving I(III)/S(VI)-ylides and two molecules of ethyl isocyanoacetate was observed. The strategy allows for the synthesis of unsymmetrical α,α-disubstituted ketones and functionalized pyrroles with up to 99% yield and wide substrate compatibility. Notably, the procedure has been extended to the late-stage modification of drugs and natural products, offering an elegant complement to the classic Passerini reaction.

Tf2O-mediated [4+2]-annulation of anthranils with 2-chloropyridines: enabling access to pyridoquinazolinones and euxylophoricine B

We present an efficient approach for synthesizing pyridoquinazolinones in the presence of triflic anhydride utilizing anthranils and 2-chloropyridines as starting materials. In this process, Tf2O initially activates anthranils forming an electrophilic 1-((trifluoromethyl)sulfonyl)benzo[c]isoxazol-1-ium species. This species undergoes an in situ annulation reaction with 2-chloropyridines, resulting in therapeutically useful pyridoquinazolinones. The reaction is tolerant to various functional groups, allowing access to a wide range of substituted pyridoquinazolinones in good yields. Furthermore, the synthesis of euxylophoricine B, known to be an antitumor agent, was also achieved.

Lithium Bromide-Promoted Formal C(sp3)-H Bond Insertion Reactions of β-Carbonyl Esters with Sulfoxonium Ylides to Synthesize 1,4-Dicarbonyl Compounds

A LiBr-promoted formal C(sp3)-H bond insertion reaction between β-carbonyl esters and sulfoxonium ylides is established. This practical reaction has a wide range of substrate scope for both β-carbonyl esters and sulfoxonium ylides to give a variety of 1,4-dicarbonyl compounds with 43-94% yields. The reaction features transition-metal-free reaction conditions and exclusive C-alkylation chemselectivity. The use of bench-stable sulfoxonium ylides overcomes previous methods that require transition metal as catalysts and unstable diazo compounds or toxic haloketones as alkylation reagents.

Synthesis of 4-styrylquinolines via direct oxidative C3-alkenylation of anthranils under Pd(II) catalysis

The palladium-catalyzed oxidative C3-alkenylation of anthranils (2,1-benzisoxazoles) with various styrenes has been successfully achieved. The C3-alkenylated anthranils were subsequently utilized in a [4+2]-cycloaddition with in situ generated α,β-unsaturated ketones leading to the synthesis of a diverse range of olefin-containing quinolines. Notably, this reaction exclusively yielded mono-alkenylated products with E-selectivity. The optimized catalytic conditions were compatible with a wide variety of substituted olefins and anthranils, forming various C3-alkenylated anthranils with good yields. To showcase the application of the present methodology, the C3-alkenylated anthranils have been employed as synthons to access a wide range of substituted quinolines.

Divergent Synthesis of Tetrasubstituted Phenols via [3 + 3] Cycloaddition Reaction of Vinyl Sulfoxonnium Ylides with Cyclopropenones

Two categories of tetrasubstituted phenols were prepared via the cycloaddition reaction of vinyl sulfoxonnium ylides with cyclopropenones in a switchable manner. Copper carbenoid was proposed as the active intermediate in the process of 2,3,4,5-tetrasubstituted phenols formation, while 2,3,5,6-tetrasubstituted phenols were generated via the direct [3 + 3] annulation of vinyl sulfoxonnium ylides with cyclopropenones under metal-free conditions. Further synthetic applications were also demonstrated.

TBAI-Catalysed Formal [4+4]-Cycloaddition: Easy Access to Oxa-Bridged Eight-Membered Heterocycles

TBAI-catalysed [4+4]-cyclization reaction of anthranils with hydrazones to deliver oxa-bridged eight-membered heterocycles in accepted yields was developed. Preliminary mechanistic studies indicated that the reaction involved the in situ generation of vinyldiazenes from readily available hydrazones followed by an aza-Michael addition of the anthranil substrates onto the vinyldiazenes and subsequent annulation. This transformation involved the formation of two new C-N bonds and C-O bond in one pot, overcoming the synthetic limitations of anthranils in organic chemistry. This strategy benefits from high efficiency and atomic economy with mild reaction conditions.

Synthesis of Indenoquinolinones and 2-Substituted Quinolines via [4 + 2] Cycloaddition Reaction

We have reported a metal-free protocol for the synthesis of indenoquinolinones and 2-substituted quinolines via [4 + 2] cycloaddition reaction using readily available 2-aminobenzaldehydes and ketones as starting materials. Different quinoline derivatives can be selectively synthesized by changing the type of ketones. O₂ and dimethyl sulfoxide (DMSO) as co-oxidants play an important role in the synthesis of indenoquinolinones. This condensation/oxidation strategy involves the formation of C-N, C-C, and C-O bonds, with the advantages of high yields and a broad substrate range.

Synthesis of Tetrahydro-2H-thiopyran 1,1-Dioxides via [1+1+1+1+1+1] Annulation: An Unconventional Usage of a Tethered C-S Synthon

An unprecedented [1+1+1+1+1+1] annulation process has been developed for the construction of tetrahydro-2H-thiopyran 1,1-dioxides. Notably, rongalite acted as a tethered C-S synthon in this reaction and can be chemoselectively used as triple C1 units and as a source of sulfone. Mechanistic investigation indicated that two different carbon-increasing models are involved in this reaction in which rongalite serves as C1 units.

Condition-Dependent Selective Synthesis of Indolo[1,2-c]quinazolines and Indolo[3,2-c]quinolines from 2-(1H-Indol-2-yl)anilines and Sulfoxonium Ylides

In this paper, a selective synthesis of indolo[1,2-c]quinazolines and indolo[3,2-c]quinolines through the cascade reactions of 2-(1H-indol-2-yl)anilines with sulfoxonium ylides is presented. The formation of products involves the generation of a carbene species from sulfoxonium ylide and its N-H bond insertion reaction with 2-(1H-indol-2-yl)aniline followed by deoxygenative imine formation, intramolecular N- or C- nucleophilic addition and deoxygenative aromatization. This switchable synthesis was condition-dependent. In the presence of K₂CO₃ in CH₃CN, the reaction mainly furnished indolo[1,2-c]quinazolines. In the presence of HOAc in dioxane, it selectively afforded indolo[3,2-c]quinolines. In addition, direct C-H/N-H functionalization of the products obtained provides a convenient and direct access to polycyclic heteroaromatic compounds. These novel protocols have advantages such as readily accessible substrates, easily tunable selectivity, good compatibility with diverse functional groups, and the use of air as a cost-free and sustainable oxidant.

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.

Asymmetric transformations from sulfoxonium ylides

Sulfoxonium ylides are important surrogates for diazo compounds, and their use in industry as safer alternatives has been evaluated during recent years. Beyond the known classical transformations, these ylides have also been used in a surprising plethora of novel and intrinsic chemical reactions, especially in recent years. Bench stability and handling are also an advantage of this class of organosulfur molecules. Despite this, efficient asymmetric transformations, specifically catalytic enantioselective versions, have only recently been reported, and there are specific reasons for this. This perspective article covers this topic from the first studies up to the latest advances, giving personal perspectives and showing the main challenges in this area in the coming years.

Rh(III)-catalyzed C-H annulation of sulfoxonium ylides with iodonium ylides towards isocoumarins

The direct synthesis of isocoumarin skeletons has been realized through the Rh(III)-catalyzed [3 + 3] annulation of sulfoxonium ylides with iodonium carbenes. The synthetic protocol was constructed efficiently with broad functional group tolerance and mild reaction conditions. This reaction can be formally viewed as the result of C-H activation, carbene insertion and nucleophilic addition processes. Furthermore, the further conversions of the product and gram-scale reactions were also demonstrate to support the effectiveness of the synthesis protocol.

Synthesis of 3-substituted quinolines by ruthenium-catalyzed aza-Michael addition and intramolecular annulation of enaminones with anthranils

A method for the synthesis of 3-substituted quinolines by ruthenium-catalyzed aza-Michael addition and intramolecular annulation of enaminones with anthranils has been developed.

Transition-Metal-, Additive-, and Solvent-Free [3 + 3] Annulation of RCF2-Imidoyl Sulfoxonium Ylides with Cyclopropenones to Give Multifunctionalized CF3-Pyridones

An efficient and practical strategy was developed to synthesize 1,3,4-triaryl-6-trifluoromethylpyridones from CF₃-imidoyl sulfoxonium ylides and cyclopropenones in good to excellent yields. This stepwise [3 + 3] annulation reaction was carried out under transition-metal-, additive-, and solvent-free conditions, generating 1 equiv of dimethyl sulfoxide as byproduct and tolerating a series of functional groups.

Copper-Catalyzed Oxidative C(sp3)-H/C(sp3)-H Cross-Coupling Reaction of 3-Methylbenzo[c]isoxazoles with Methyl Ketones: Access to Indigoid Analogues

A copper-catalyzed oxidative C(sp³)-H/C(sp³)-H cross-coupling reaction of methyl ketones and 3-methylbenzo[c]isoxazoles has been developed for the direct synthesis of 3-oxoindolin-2-ylidene derivatives. This process involves an intermolecular nucleophilic addition/ring-opening/aza-Michael addition cascade, providing indigoid analogues with high atom economy and as single isomers exclusively under mild conditions.

Annulation of CF3-Imidoyl Sulfoxonium Ylides with 1,3-Dicarbonyl Compounds: Access to 1,2,3-Trisubstituted 5-Trifluoromethylpyrroles

A lithium-bromide-promoted nucleophilic substitution/annulation cascade reaction between CF₃-imidoyl sulfoxonium ylides and 1,3-dicarbonyl compounds has been established, and the corresponding 1,2,3-trisubstituted 5-trifluoromethylpyrroles have been obtained in 27-78% yield. This reaction features a broad substrate scope and generates dimethyl sulfoxide and H₂O as byproducts.

Pd-Catalyzed Sequential Formation of C-C Bonds: A New Strategy for the Synthesis of (E)-α,β-Unsaturated Carbonyl Compounds from Sulfoxonium Ylides and 1-Iodo-2-((2-methylallyl)oxy)benzene Compounds

α,β-Unsaturated carbonyl compounds are significant moieties in many biological molecules and have attracted considerable attention in organic synthetic chemistry. A Pd-catalyzed cascade cyclization for the synthesis of (E)-α,β-unsaturated carbonyl compounds with the sequential formation of C-C bonds was developed. This method offers high efficiency, good functional group tolerance, and moderate to excellent yields and generally displays high stereoselectivity.

Ruthenium-catalyzed room-temperature coupling of α-keto sulfoxonium ylides and cyclopropanols for δ-diketone synthesis

Previous transition metal-catalyzed synthesis processes of δ-diketones are plagued by the high cost of the rhodium catalyst and harsh reaction conditions. Herein a low-cost, room temperature ruthenium catalytic method is developed based on the coupling of α-keto sulfoxonium ylides with cyclopropanols. The mild protocol features a broad substrate scope (47 examples) and a high product yield (up to 99%). Mechanistic studies argue against a radical pathway and support a cyclopropanol ring opening, sulfoxonium ylide-derived carbenoid formation, migratory insertion C-C bond formation pathway.

I2-DMSO mediated oxidative amidation of methyl ketones with anthranils for the synthesis of α-ketoamides

An I₂-DMSO mediated oxidative amidation of methyl ketones using anthranils as masked N-nucleophiles has been developed for the direct synthesis of α-ketoamides with high atom-economy. This metal-free process involves reductive N-O bond cleavage of anthranils and oxidative C-N bond formation of methyl ketones under mild conditions. The iodo group and electrophilic formyl group provide multiple possibilities for further functionalization of α-ketoamides.

Synthesis of disubstituted γ-butyrolactones and spirocyclopropanes via a multicomponent reaction of aldehydes, Meldrum's acid and sulfoxonium ylides

An efficient synthesis of disubstituted γ-butyrolactones and spirocyclopropanes via multicomponent reaction of aldehydes, Meldrum's acid and sulfoxonium ylides has been developed.

Indolizine synthesis via radical cyclization and demethylation of sulfoxonium ylides and 2-(pyridin-2-yl)acetate derivatives

A novel radical cross-coupling/cyclization of 2-(pyridin-2-yl)acetate derivatives and sulfoxonium ylides is developed, which provides a straightforward access to structurally diverse methylthio-substituted indolizine.

Ruthenium(II)-Catalyzed Homocoupling of α-Carbonyl Sulfoxonium Ylides Under Mild Conditions: Methodology Development and Mechanistic DFT Study

A mild ruthenium(II)-catalyzed homocoupling of α-carbonyl sulfoxonium ylides was developed and the detailed mechanism was understood based on DFT calculations in the current report. The catalytic system utilizes the α-carbonyl sulfoxonium ylide as both the directing group for ortho-sp2 C-H activation and the acylmethylating reagent for C-C coupling. Various substituents are compatible in the transformation and a variety of isocoumarin derivatives were synthesized at room temperature without any protection. The theoretical results disclosed that the full catalytic cycle contains eight elementary steps, and in all the cationic Ru(II) monomer is involved as the catalytic active species. The acid additive is responsible for protonation of the ylide carbon prior to the intramolecular nucleophilic addition and C-C bond cleavage. Interestingly, the intermediacy of free acylmethylation intermediate or its enol isomer is not necessary for the transformation.

Enantioselective S-H Insertion Reactions of α-Carbonyl Sulfoxonium Ylides

The first example of enantioselective S-H insertion reactions of sulfoxonium ylides is reported. Under the influence of thiourea catalysis, excellent levels of enantiocontrol (up to 95 % ee) and yields (up to 97 %) are achieved for 31 examples in S-H insertion reactions of aryl thiols and α-carbonyl sulfoxonium ylides.

Copper-Catalyzed Electrophilic Amination of Arylboronic Acids with Anthranils: An Access to N-Aryl-2-aminophenones

An efficient copper-catalyzed electrophilic amination strategy has been established for the rapid synthesis of N-aryl-2-aminophenones from readily available arylboronic acids/esters and anthranils. This protocol features good functional group tolerance, broad substrate scope, and operational simplicity. Moreover, a tandem C-H borylation and C-N coupling protocol has also been developed to transform simple arenes to the valuable N-aryl-2-aminophenones in one pot. Additionally, the synthetic potential of this methodology is further demonstrated by the synthesis of various useful N-heterocycles and derivatives.

Anthranils: versatile building blocks in the construction of C–N bonds and N-heterocycles

This review article provides an overview of the recent progress in the transformations of anthranils, which have emerged as versatile building blocks in the assembly of various C–N bonds and medicinally active heterocyclic systems.