Microwave-Assisted Cp*CoIII-Catalyzed C–H Activation/Double C–N Bond Formation Reactions to Thiadiazine 1-Oxides

Transition-Metal-Free Sulfoximidation of Sulfonylhydrazones for the Synthesis of N-Sulfanylidenehydrazonamides

Herein, we report a transition-metal-free C-H bond sulfoximidation protocol of sulfonyl hydrazones with hypervalent iodine(III) reagents. A library of novel N-sulfaneylidenehydrazonamides was constructed via chemoselective C-N bond formation reactions at aldehyde C-H bonds of sulfonyl hydrazones in the presence of a base. The reaction demonstrated broad substrate group diversity under exceedingly mild reaction conditions, and excellent yields were achieved at room temperature.

Chiral Brønsted Acid-Catalyzed Kinetic Resolution of Sulfoximines for the Synthesis of Benzothiadiazine-1-Oxides

Benzothiadiazine-1-oxide scaffolds with S-stereogenic centers are prevalent in bioactive and pharmaceutical molecules. Reported works mainly focused on the metal-catalyzed asymmetric C-H amination/cyclization reaction for the synthesis of benzothiadiazine-1-oxides. Here, we reported a chiral phosphoric acid-catalyzed kinetic resolution of sulfoximines, providing chiral benzothiadiazine-1-oxides and recovered chiral sulfoximines with moderate to good enantioselectivities (s factors up to 36.6).

Cobalt-Catalyzed Enantio- and Regioselective C(sp3 )-H Alkenylation of Thioamides

An enantioselective cobalt-catalyzed C(sp3 )-H alkenylation of thioamides with but-2-ynoate ester coupling partners employing thioamide directing groups is presented. The method is operationally simple and requires only mild reaction conditions, while providing alkenylated products as single regioisomers in excellent yields (up to 85 %) and high enantiomeric excess [up to 91 : 9 enantiomeric ratio (er), or up to >99 : 1 er after a single recrystallization]. Diverse downstream derivatizations of the products are demonstrated, delivering a range of enantioenriched constructs. Extensive computational studies using density functional theory provide insight into the detailed reaction mechanism, origin of enantiocontrol, and the unusual regioselectivity of the alkenylation reaction.

Iridium(III)-Catalyzed C-H Cyclization of Sulfoximines with Diazo Meldrum's Acids for the Synthesis of Cyclic Sulfoximines

Iridium(III)-catalyzed C-H cyclization of sulfoximines with diazo Meldrum's acid provided cyclic sulfoximines with a carbonyl group in good to excellent yields. These compounds were easily converted into unsubstituted and arylated sulfoximines. Moreover, the vinyl triflates obtained from the cyclic sulfoximines underwent palladium(II)-catalyzed cross-coupling reactions with a variety of aryl, arylalkynyl, and heteroatom (N and S) nucleophiles, affording a wide range of monosubstituted sulfoximines in high yields.

Microwave-accelerated cross-dehydrogenative-coupling (CDC) of N-(quinolin-8-yl)amides with acetone/acetonitrile under metal-free conditions

A highly selective remote C(sp³)-H acetonation of N-(quinolin-8-yl)amide scaffolds at the C5-position under microwave irradiation has been developed. In the absence of a transition-metal-catalyst, benzoyl peroxide (BPO)-promoted cross-dehydrogenation coupling (CDC) of N-(quinolin-8-yl)amides with acetone/acetonitrile occurred smoothly to generate the corresponding 5-acetonated/acetonitriled N-(quinolin-8-yl)amides in good yields. The transformation is operationally simple, rapid, easily scaled-up to the gram scale, and shows a broad substrate scope.

Sulfoximine Assisted C-H Activation and Annulation via Vinylene Transfer: Access to Unsubstituted Benzothiazines

In this study, we report the synthesis of unsubstituted 1,2-benzothiazines through a redox-neutral Rh(III)-catalyzed C-H activation and [4+2]-annulation of S-aryl sulfoximines with vinylene carbonate. Notably, the introduction of an N-protected amino acid ligand significantly enhances the reaction rate. The key aspect of this redox-neutral process is the utilization of vinylene carbonate as an oxidizing acetylene surrogate and an efficient vinylene transfer agent. This vinylene carbonate enables the cyclization with the sulfoximine motifs, successfully forming a diverse array of 1,2-benzothiazine derivatives in moderate to good yields. Importantly, this study highlights the potential of Rh(III)-catalyzed C-H activation and [4+2]-annulation reactions for the synthesis of optically pure 1,2-benzothiazines with high enantiomeric purity.

Recent Advances in the Synthesis of Cyclic Sulfoximines via C-H Bond Activation

Sulfoximines, a ubiquitous class of structural motifs, are widely present in bioactive molecules and functional materials that have received considerable attention from modern organic chemistry, pharmaceutical industries, and materials science. Sulfoximines have proved to be an effective directing group for C-H functionalization which was widely investigated for the synthesis of cyclic sulfoximines. Within the last decade, great progress has been achieved in the synthesis of cyclic sulfoximines. Thus, this review highlights the recent advances in the synthesis of cyclic sulfoximines via the C-H activation strategy and is classified based on the substrate types.

Cobalt(III)/Chiral Carboxylic Acid-Catalyzed Enantioselective Synthesis of Benzothiadiazine-1-oxides via C-H Activation

Among sulfoximine derivatives containing a chiral sulfur center, benzothiadiazine-1-oxides are important for applications in medicinal chemistry. Here, we report that the combination of an achiral cobalt(III) catalyst and a pseudo-C₂ -symmetric H₈ -binaphthyl chiral carboxylic acid enables the asymmetric synthesis of benzothiadiazine-1-oxides from sulfoximines and dioxazolones via enantioselective C-H bond cleavage. With the optimized protocol, benzothiadiazine-1-oxides with several functional groups can be accessed with high enantioselectivity.

Rh(III)-catalysed C-H/C-H cross-coupling of S-aryl sulfoximines with thiophenes: facile access to [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and benzothiazines

Reported herein is rhodium-catalysed oxidative C-H/C-H cross-coupling of S-aryl sulfoximines with thiophenes via a chelation-assisted strategy, which provides an efficient approach for the construction of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and benzothiazine skeletons from easily available substrates. This protocol exhibits a good compatibility with halogen substituents, thus paving the way for further transformation to prepare various organic functional molecules. The resulting benzothiazine derivative shows a deep blue emission with Commission Internationale de 'Eclairage (CIE) coordinates of (0.15, 0.04), a high quantum yield, and a delayed fluorescence lifetime.

Cp*CoIII-catalyzed formal [4 + 2] cycloaddition of 2-phenyl-1H-imidazoles to afford imidazo[1,2-c]quinazoline derivatives

A synthetic protocol based on Cp*Co^III-catalyzed C-H amidation/annulation of 2-aryl-1H-imidazoles with 1,4,2-dioxazol-5-ones was developed to give imidazo[1,2-c]quinazoline derivatives with broad substrate scope in moderate to good yields. The method has good prospects of application in the synthesis of imidazo[1,2-c]quinazoline drugs.

Acid-Catalyzed Hydrolysis and Intramolecular Cyclization of N-Cyano Sulfoximines for the Synthesis of Thiadiazine 1-Oxides

Herein, we describe a novel approach for the practical synthesis of thiadiazine 1-oxides 10. The first example of an intramolecular cyclization with 2-N-cyano-sulfonimidoyl amides 9 to form the desired thiadiazine 1-oxides 10 was developed. One-pot acid-induced hydrolysis of the cyano group and the intramolecular cyclocondensation protocol readily provided various heterocyclic frameworks in good to moderate yields. Notably, the crystal structures of N-urea sulfoximine 11 and thiadiazine 1-oxide 10i have been determined using X-ray crystallography.

Synthesis and Transformations of NH-Sulfoximines

Recent years have seen a marked increase in the occurrence of sulfoximines in the chemical sciences, often presented as valuable motifs for medicinal chemistry. This has been prompted by both pioneering works taking sulfoximine containing compounds into clinical trials and the concurrent development of powerful synthetic methods. This review covers recent developments in the synthesis of sulfoximines concentrating on developments since 2015. This includes extensive developments in both S-N and S-C bond formations. Flow chemistry processes for sulfoximine synthesis are also covered. Finally, subsequent transformations of sulfoximines, particularly in N-functionalization are reviewed, including N-S, N-P, N-C bond forming processes and cyclization reactions.

One-Pot Construction of Indolo[2,3-b]quinoxalines through Ruthenium-Catalyzed Ortho C-H Bond Functionalization of 2-Arylquinoxalines with Sulfonyl Azides

The synthesis of N-substituted indolo[2,3-b]quinoxalines has been developed through a Ru(II)-catalyzed ortho C-H functionalization of 2-arylquinoxalines with sulfonyl azides and further oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in one pot. This double C-N bond formation strategy provides a new efficient route for the preparation of a series of biologically relevant 6H-indolo[2,3-b]quinoxaline derivatives in up to 94% yield, suggesting a broad substrate scope applicability. The preliminary mechanistic studies reveal that the sequential C-N bond formations proceed through the formation of a five-membered ruthenacyclic intermediate in the first step and a radical mechanism in the second step.

Pd-Catalyzed double carbopalladation/syn-insertion cascade reactions toward medium-size sulfoximine heterocycles

With the assistance of Ac in sulfoximine as a protecting group (PG) and MeOH as a de-PG agent, Pd-catalyzed multicomponent reactions were developed to access indene-fused medium-size sulfoximine heterocycles. The reactions proceeded smoothly under exceptionally mild conditions to produce polyheterocyclic sulfoximines with regiospecificity and good functional group tolerance. A double carbopalladation/syn-insertion of triple bond sequences was proposed tothis transformation.

One-pot multi-step cascade protocols toward β-indolyl sulfoximidoyl amides via intermolecular trapping of an α-indolylpalladium complex by CO

Various β-indolyl sulfoximidoyl amides were efficiently prepared from ortho-iodoanilines, propargyl bromides, 1 atm of CO, and substituted NH-sulfoximines, through a palladium-catalyzed indole annulation/carbonyl insertion/C-N bond formation cascade. Mostly good to high yields of the products were obtained through this multi-step, one-pot reaction protocol under very gentle reaction conditions. The obtained β-indolyl sulfoximidoyl amides could be converted into biologically interesting sulfoximine analogues that contain a tryptamine moiety.

Metal-free regioselective C-H amination for the synthesis of pyrazole-containing 2H-indazoles

A general and practical regioselective approach for the C-H amination of 2H-indazoles under transition-metal-free conditions was developed. A series of substrates were tested showing eminent functional group tolerance and affording the C-N functionalization products in good to excellent yields. Mechanism studies revealed that a radical process was involved in this transformation.

Synthesis of N-acylbenzimidazoles through [4 + 1] annulation of N-arylpivalimidamides with dioxazolones

Presented herein is a novel and efficient synthesis of N-acylbenzimidazoles through an unprecedented [4 + 1] annulation of N-arylpivalimidamides with dioxazolones.

Metal-free C-H Activation over Graphene Oxide toward Direct Syntheses of Structurally Different Amines and Amides in Water

Unprecedented metal-free synthesis of a variety of amines and amides is reported via amination of C(sp³)-H and C(sp²)-H bonds. The strategy involves graphene-oxide/I₂-catalyzed nitrene insertion using PhINTs as a nitrene (NT) source in water at room temperature. A wide range of structurally different substrates, viz., cyclohexane, cyclic ethers, arenes, alkyl aromatic systems, and aldehydes/ketones, having an α-phenyl ring have been employed successfully to afford the corresponding nitrene insertion product in good yield, albeit low in few cases. The envisaged method has superiority over others in terms of its operational simplicity, metal-free catalysis, use of water as a solvent, ambient reaction conditions, and reusability of the catalyst.

Synthesis of Benzothiadiazine-1-oxides by Rhodium-Catalyzed C-H Amidation/Cyclization

A rhodium-catalyzed C-H amidation/cyclization sequence provides benzothiadiazine-1-oxides from sulfoximines and 1,4,2-dioxazol-5-ones in good yields. The reaction is characterized by a high functional group tolerance and, in contrast to most previous transformations of this type, is well-suited for S-alkyl-S-aryl-substituted sulfoximines.

A one-pot method for the synthesis of 3-(hetero-)aryl-1,4,2-dioxazol-5-ones

3-R-1,4,2-dioxazol-5-ones are a class of compounds that are increasingly finding diverse uses, including as regioselective amidation reagents and as electrolyte additives that enable long cycling lifetimes in rechargeable lithium-ion batteries. Conventional methods for their synthesis tend to be slow and time-consuming, requiring isolation and thorough drying of a hydroxamic acid intermediate, followed by a separate cyclization step with N,N′-carbonyldiimidazole. Furthermore, the cyclization is typically performed in dichloromethane, an environmentally harmful solvent. This work demonstrates a new one-pot method for the synthesis of these compounds that eliminates the need for isolation of the intermediate or the use of halogenated solvents. The reaction is mainly performed using environmentally benign ethyl acetate and a relatively small amount of N,N-dimethylformamide. The reaction proceeds readily at room temperature and requires no expensive metal catalysts to function.

Facile synthesis of N-1,2,4-oxadiazole substituted sulfoximines from N-cyano sulfoximines

A divergent approach has been successfully developed for the synthesis of N-1,2,4-oxadiazole substituted sulfoximines starting from N-cyano sulfoximines. This method has a wide degree of substrate scope that includes aryl, heteroaryl, alkyl, fluoroalkyl and saturated heterocyclic compounds. Excellent functional group tolerability was also observed. Extension of this methodology to nucleosides, amino acids and dipeptides was found to be successful. A gram scale reaction was also established. The major part of this method is metal free and the utility of environmentally friendly solvents such as 2-methyl THF and ionic liquids is an added advantage.

Synthesis of thiazolo[2,3-b]quinazoline derivatives via base-promoted cascade bicyclization of o-alkenylphenyl isothiocyanates with propargylamines

A highly efficient cascade bicyclization reaction of o-alkenylphenyl isothiocyanates with propargylamines has been developed, which affords a series of thiazolo[2,3-b]quinazolines in good to excellent yields by using K₂CO₃ as a base in MeCN at 80 °C. This method is transition-metal-free and operationally simple with broad functional group tolerance. Mechanistically, 6-exo-trig hydroamination followed by 5-exo-dig hydrothiolation was involved in this transformation.

Rhodium(III)-Catalyzed Regioselective C(sp2)-H Functionalization of 7-Arylpyrazolo[1,5-a]pyrimidines with Dioxazolones as Amidating Agents

Rh(III)-catalyzed C-H functionalization of 7-arylpyrazolo[1,5-a]pyrimidines was developed wherein the pyrazolo[1,5-a]pyrimidine moiety is reported for the first time to direct the C-H bond activation. Various 7-arylpyrazolo[1,5-a]pyrimidines underwent smooth C-H amidation with alkyl-, aryl-, and heteroaryl-substituted dioxazolones to afford the products in moderate to good yields. Mechanistic studies suggest that a six-membered rhodacycle intermediate involving N1 might play a key role in the regioselective catalytic cycle.

Cobalt(iii)-catalyzed C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals

Cobalt(iii)-catalyzed mild C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals has been realized.

Cp*CoIII-catalyzed formal [4+2] cycloaddition of benzamides to afford quinazolinone derivatives

A Cp*Co^III-catalyzed arene C–H bond amidation/annulation of benzamides was developed to afford quinazolinone derivatives in one-pot with high yields and broad substrate scope.

Rhodium(iii)-catalyzed tandem reaction: efficient synthesis of dihydrobenzo thiadiazine 1-oxide derivatives

A tandem annulation reaction triggered by rhodium(iii)-catalyzed C–H bond functionalizations has been well developed for highly efficient synthesis of dihydrobenzo thiadiazine 1-oxide derivatives from free NH-sulfoximine and two-component benzyl azides.

Rhodium(iii)-catalyzed tandem annulation reaction to build polycyclic benzothiazine derivatives

An efficient rhodium(iii)-catalyzed C–H bond functionalization to construct polycyclic benzothiazine derivatives has been well developed.

Pd/P/dba-Promoted cascade annulations to produce fused medium-sized sulfoximine polyheterocycles

The Pd-catalyzed multicomponent reactions of NH-sulfoximine, aryl iodide and norbornadiene (NBD) are reported to chemoselectively produce fused medium-sized sulfoximine polyheterocycles in good to excellent yields.