Copper-Catalyzed Intramolecular N–S Bond Formation by Oxidative Dehydrogenative Cyclization

Chemodivergent Synthesis of Benzothiadiazin-3-one 1-Oxides and Benzisothiazol-3-ones via Visible Light-Promoted Intramolecular N-S Bond Formation

We reported a versatile protocol to chemodivergently construct significant heterocyclic scaffolds of benzothiadiazin-3-one 1-oxides and benzisothiazol-3-ones by visible light-promoted photocatalysis. This substrate-dependent chemoselective strategy enables N-(2-mercaptophenyl)-N'-substituted ureas through the N-S bond coupling/oxidation cascade to selectively produce benzothiadiazin-3-one 1-oxides; however, the transformation of 2-mercaptobenzamides only occurs via N-S bond coupling to access benzisothiazol-3-ones with moderate to good yields. This strategy features mild conditions, excellent chemoselectivity, and functional group compatibility, which has potential applications in organic and medicinal chemistry.

Progress in copper-catalysed/mediated intramolecular dehydrogenative coupling

Transition metal-catalysed C-H functionalization reactions are one of the most efficient synthetic methodologies to construct carbon-carbon and carbon-heteroatom bonds. The initial developments in the field were largely dominated by expensive transition metal catalysts. However, in the past decade, the focus of the catalyst shifted to first-row transition metals and copper catalysis contributed significantly. Abundant, cost-effective, and less toxic copper catalysts are an ideal green alternative to palladium and similar metals. The intramolecular dehydrogenative coupling itself developed as a prominent area of focus as the strategy straightaway affords complex polycyclic scaffolds in one pot. Regioselective activation of inert C-H bonds were made possible with copper catalysts and interestingly, oxygen served as the terminal oxidant in most of the cases. In the present review the focus is on the intramolecular dehydrogenative coupling reactions between carbon-hydrogen and heteroatom-hydrogen bonds to afford carbon-carbon and carbon-hetero atom bonds, catalysed/mediated by copper salts. Though the intermolecular dehydrogenative coupling reactions of copper have already been reviewed more than once, to the best of our knowledge this is the first comprehensive account of copper-based intramolecular dehydrogenative coupling.

Synthesis of novel series of 3,5-disubstituted imidazo[1,2-d] [1,2,4]thiadiazoles involving SNAr and Suzuki–Miyaura cross-coupling reactions

The first access to 3,5-disubstituted imidazo[1,2-d][1,2,4]thiadiazole derivatives is reported. The series were generated from 2-mercaptoimidazole, which afforded the key intermediate bearing two functional positions. The S_NAr reactivity toward tosyl release at the C-3 position was investigated and a regioselective electrophilic iodination in C-5 position was performed to allow a novel C–C bond using Suzuki–Miyaura reaction. Palladium-catalyzed cross-coupling conditions were optimized. A representative library of various boronic acids was employed to establish the scope and limitations of the method. To complete this methodological study, the influence of the nature of the C-3 imidazo[1,2-d][1,2,4]thiadiazole substitutions on the arylation in C-5 was investigated.

A convenient design of 3,5-disubstituted imidazo[1,2-d][1,2,4]thiadiazoles is reported from 2-mercaptoimidazole, which afforded a versatile platform that was then used to access a variety of original heterocycles.

Ligand-free access to benzisothiazolones and benzisoselenazolones through NiFe2O4 catalyzed concomitant annulation of 2-halobenzanilides with chalcogens and their late-stage transformations

A practical non-hazardous one-pot protocol for the synthesis of benzisothiazolones and benzisoselenazolones, involving magnetically retrievable nano-nickel ferrite catalyzed tandem annulation between 2-halobenzanilides and elemental S8 or Se.

Oxidative cross-coupling of thiols for S-X (X = S, N, O, P, and C) bond formation: mechanistic aspects

This review focuses on the reactive intermediates (disulfides, sulfenyl halides, thiyl radicals, sulfenium cations, and metal-organosulfur species) and the mechanisms of the recently reported oxidative couplings of thiols. These intermediates are generated by chemical oxidants, transition metal catalysts, electrochemistry, and photochemistry. Chemical oxidant-mediated reactions involve radical, halogenated, or cationic intermediates, or disulfides. Transition metal-catalyzed mechanisms proposed various metal-organosulfur intermediates to elucidate the reactivity and selectivity of metal catalysts. In electro- and photooxidation, direct oxidation/reduction mechanisms of reactants at the electrode or indirect oxidation/reduction of reactants in the presence of redox catalysts have been reported. The following sections are based on the products, thiosulfonates (S-S bond), sulfenamides, sulfinamides, and sulfonamides (S-N bond), sulfinates (S-O bond), thiophosphine oxides and thiophosphates (S-P bond), and sulfides, sulfoxides, and sulfones (S-C bond) and discuss the reaction mechanisms and the above-mentioned key intermediates for product formation. The contents of this review will provide helpful information, guiding the choice of oxidative coupling conditions for the synthesis of various organosulfur compounds with high yields and selectivity.

Recent Advances in Iodine-Promoted C-S/N-S Bonds Formation

Sulfur-containing scaffold, as a ubiquitous structural motif, has been frequently used in natural products, bioactive chemicals and pharmaceuticals, particularly C-S/N-S bonds are indispensable in many biological important compounds and pharmaceuticals. Development of mild and general methods for C-S/N-S bonds formation has great significance in modern research. Iodine and its derivatives have been recognized as inexpensive, environmentally benign and easy-handled catalysts or reagents to promote the construction of C-S/N-S bonds under mild reaction conditions, with good regioselectivities and broad substrate scope. Especially based on this, several new strategies, such as oxidation relay strategy, have been greatly developed and accelerated the advancement of this field. This review focuses on recent advances in iodine and its derivatives promoted hybridized C-S/N-S bonds formation. The features and mechanisms of corresponding reactions are summarized and the results of some cases are compared with those of previous reports. In addition, the future of this domain is discussed.

Nickel(ii)-catalyzed C(sp2)-H sulfuration/annulation with elemental sulfur: selective access to benzoisothiazolones

The first nickel(ii)-catalyzed direct sulfuration/annulation of C(sp²)-H bonds with elemental sulfur has been achieved by using 2-amino alkylbenzimidazole (MBIP-amine) as a N,N-bidentate directing group. This strategy tolerates a wide range of functional groups, furnishing structurally diverse benzoisothiazolone derivatives with benzimidazole skeletons in moderate to excellent yields in a simple and efficient way.

Transition-metal-free S–N bond formation: synthesis of 5-amino-1,2,4-thiadiazoles from isothiocyanates and amidines

A novel and green method for the synthesis of 5-amino-1,2,4-thiadiazoles has been developed by the reaction of isothiocyanates with amidines.

Copper-Catalyzed Aerobic Oxidative [3+2] Annulation for the Synthesis of 5-Amino/Imino-Substituted 1,2,4-Thiadiazoles through C-N/N-S Bond Formation

A copper-catalyzed aerobic oxidative annulation reaction of 2-aminopyridine/amidine with isothiocyanate has been reported. This strategy involving C-N/N-S bond formations provides various 5-amino/imino-substituted 1,2,4-thiadiazole derivatives under a Cu/O₂ catalytic system. This method has demonstrated high reactivity, mild reaction conditions, and a broad substrate scope. Furthermore, the synthetic utilities of the approach are demonstrated by further modifications.

Aerobic, Diselenide-Catalyzed Redox Dehydration: Amides and Peptides

At 2.5 mol % loadings using reaction temperatures between 30-55 °C, ortho-functionalized diaryl diselenides are highly effective organocatalytic oxidants for aerobic redox dehydrative amidic and peptidic bond formation using triethyl phosphite as a simple terminal reductant. This simple-to-perform organocatalytic reaction relies on the ability of selenols to react directly with dioxygen in air without recourse to metal catalysts. It represents an important step toward the development of a general, economical, and benign catalytic redox dehydration protocol.

Recent advances in sulfur–nitrogen bond formation via cross-dehydrogenative coupling reactions

This focus-review surveys literature methods for the construction of sulfur–nitrogen bonds through cross-dehydrogenative coupling reactions between thiols and N–H compounds with a particular emphasis on the mechanistic aspects of the reactions. The literature has been surveyed until the end of 2017.

This review surveys the construction of sulfur–nitrogen bonds through cross-dehydrogenative coupling reactions between thiols and N–H compounds.

Synthesis ofN-sulfenyl-sulfoximines and -sulfenamides through a metal-free N–H/S–H dehydrocoupling reaction

A metal-free, iodine-catalyzed N–H/S–H dehydrocoupling reaction of sulfoximines and anilines with various thiols to construct sulfur–nitrogen bonds has been developed.

One-pot synthesis of 3,5-disubstituted 1,2,4-thiadiazoles from nitriles and thioamides via I2-mediated oxidative formation of an N–S bond

The one-pot reaction includes sequential intermolecular addition of thioamides to nitriles, and intramolecular oxidative coupling of N–H and S–H bonds mediated by molecular iodine.

Double 1,4-addition of (thio)salicylamides/thiosalicylic acids with propiolate derivatives: a direct, general synthesis of diverse heterocyclic scaffolds

A simple and practical ring-closure procedure to prepare a range of diverse heterocycles has been developed.

An efficient approach to construct benzisothiazol-3(2H)-ones via copper-catalyzed consecutive reaction of 2-halobenzamides and carbon disulfide

An efficient copper-catalyzed reaction for the synthesis of benzisothiazol-3(2H)-ones has been developed, starting from easily available 2-halobenzamides and carbon disulfide, which gave the corresponding target products in 30-89% yield for 25 examples. The reaction proceeds via a consecutive process with S-C bond and S-N bond formation.

Benzoisothiazolone Organo/Copper-Cocatalyzed Redox Dehydrative Construction of Amides and Peptides from Carboxylic Acids using (EtO)3P as the Reductant and O2 in Air as the Terminal Oxidant

Carboxylic acids and amine/amino acid reactants can be converted to amides and peptides at neutral pH within 5-36 h at 50 °C using catalytic quantities of a redox-active benzoisothiazolone and a copper complex. These catalytic "oxidation-reduction condensation" reactions are carried out open to dry air using O2 as the terminal oxidant and a slight excess of triethyl phosphite as the reductant. Triethyl phosphate is the easily removed byproduct. These simple-to-run catalytic reactions provide practical and economical procedures for the acylative construction of C-N bonds.

N-Tosyl-1,5,2,6-dithiadiazocane: a waste-free electrophilic sulfur reagent for the efficient synthesis of medium-ring S,N-heterocycles

Medium-ring S,N-heterocycles can be easily accessed in a one-pot procedure using an eight-membered dimeric sulfenamide annulation reagent.

Direct synthesis of N-sulfenylimines through oxidative coupling of amines with disulfides/thiols over copper based metal–organic frameworks

A highly porous metal–organic framework based on supramolecular building blocks with pcu-topology has been tested for the oxidative coupling of amines and disulfides to afford the N-sulfenylimines directly in good yields.

Copper-catalyzed N-thioetherification of sulfoximines using disulfides

A novel copper-catalyzed N-thioetherification of sulfoximines under mild reaction conditions was developed using readily available disulfides as the sulfur source.

Construction of N-containing heterocycles via oxidative intramolecular N–H/X–H coupling

The preparation of N-containing heterocycles using oxidative coupling has become a hot topic recently. This feature article summarized the methodology related to the construction of N-heterocycles through intramolecular oxidative N–H/X–H coupling.