Elemental Sulfur and Molecular Iodine as Efficient Tools for Carbon-Nitrogen Bond Formation through Redox Reactions

Sulfur-Mediated Decarboxylative Amidation of Cinnamic Acids via C═C Bond Cleavage

A new strategy for the synthesis of amides has been developed using sulfur-mediated decarboxylative coupling of cinnamic acids with amines via oxidative cleavage of the C═C bond.

Sulfur- and DABCO-Promoted Reaction between Alkylidene Rhodanines and Isothiocyanates: Access to Aminoalkylidene Rhodanines

In this work, an efficient sulfur- and DABCO-promoted reaction for the synthesis of aminoalkylidene rhodanines from available alkylidene rhodanines and isothiocyanates is reported. A tandem process including sulfurative annulation/ring-opening by liberation of a CS2 molecule/olefination allows the synthesis of aminoalkylidene rhodanines with acceptable functional group tolerance. Chemo- and stereoselectivity, operational simplicity, and synthetically useful yields are some highlighted advantages of these transformations.

Base- and sulfur-promoted oxidative lactonization of chalcone-acetate Michael adducts: access to pyran-2-ones

A cost-effective, practical, straightforward and scalable synthesis of α-pyrones via base- and sulfur-promoted annulation of phenylacetates and chalcones is reported. Generated in situ from the starting components by using dbu as a base catalyst, the Michael adducts underwent a smooth oxidative cyclization into 3,4,6-triaryl-2-pyranones upon heating with DABCO and sulfur in DMSO. Extension to malonate in place of phenylacetates led to 4,6-diaryl-2-pyranone-2-carboxylates.

Three-Component Reaction between 3-Acetylcoumarins, Amines, and Elemental Sulfur: A Designed Approach to 3-Amino-4H-thieno[3,2-c]coumarins

In this work, a series of novel 3-amino-4H-thieno[3,2-c]coumarins were designed and synthesized by a one-pot, catalyst-free, and three-component reaction of 3-acetylcoumarins with amines and elemental sulfur. Readily available starting materials, simple heating conditions, facile installation of a sulfur atom into the molecule using S8 as a sulfur source, acceptable functional group tolerance, and synthetically useful yields are some highlighted benefits of this process.

Elemental Sulfur Promoted Cyclization of Aryl Hydrazones and Aryl Isothiocyanates Yielding 2-Imino-1,3,4-thiadiazoles

We report a method for using elemental sulfur to facilitate the cyclization of aryl hydrazones and aryl isothiocyanates, affording biorelated 2-imino-1,3,4-thiadiazoles. Reactions progressed in the presence of elemental sulfur, N-methylmorpholine base, and DMSO solvent, while were tolerant of a wide range of functionalities including halogen, nitro, cyano, methylsulfonyl, and heterocyclic groups. The method appears to offer a general pathway for using simple, cheap, and stable reagents to afford triaryl-substituted 2-imino-1,3,4-thiadiazoles under relatively mild conditions.

Sulfur- and Amine- Promoted Multielectron Autoredox Transformation of Nitromethane: Multicomponent Access to Thiourea Derivatives

Thiourea derivatives are in-demand motifs in organic synthesis, medicinal chemistry and material science, yet redox methods for the synthesis that start from safe, simple, inexpensive and readily available feedstocks are scarce. In this article, we disclose the synthesis of these motifs using elemental sulfur and nitromethane as the starting materials. The method harnesses the multi-electron auto-redox property of nitromethane in the presence of sulfur and amines, delivering thiourea products without any added oxidant or reductant. Extension of this reaction to cyclizable amines and/or higher homologues of nitromethane led to a wide range of nitrogen heterocycles and thioamides. Operationally simple, the reactions are scalable, tolerate a wide range of functional groups, and can be employed for the direct functionalization of natural products. Mechanistically, the nitro group was found to act as an oxidant leaving group, being reduced to ammonia whereas sulfur, along with the role of a sulfur building block for the thiocarbonyl group, behaved as a complementary reductant, being oxidized to sulfate.

Crystal structure of 4-(naphthalen-2-yl)-2-oxo-6-phenyl-1,2-di-hydro-pyridine-3-carbo-nitrile

The synthesis and crystal structure of the title compound, C22H14N2O, are described. The title compound was synthesized by a three-component one-pot reaction in DMSO involving chalcone, cyano-acetamide and elemental sulfur as catalyst. The compound was characterized by spectroscopic methods and single-crystal X-ray diffraction. The structure consists of inversion-related dimers produced by N-H⋯O hydrogen bonding, which further inter-act through π-π contacts.

Sulfur-Promoted Oxidative Cyclization of Pentan-1-ones: Direct Access to Tetrasubstituted Furans from Deoxybenzoins and Chalcones

Furan is an important heterocyclic scaffold in natural product, bioorganic, and medicinal chemistry as well as in materials science. The system S8/DABCO/DMSO was found to efficiently mediate the oxidative cyclization of 1,2,3,5-tetraarylpentan-1-ones A, which were obtained in situ as the Michael adducts of chalcones 1 and deoxybenzoins 2, to furan 3. The strategy provided convenient and direct access to tetrasubstituted furans 3 from readily available starting materials with high functional group tolerance.

Dihydropyrrole-3-thiones: one-pot synthesis from propargylamines, acyl chlorides and sodium sulfide

An efficient one-pot synthesis of 1,2,5-trisubstituted-1,2-dihydro-3H-pyrrole-3-thiones (up to 91% yield), representatives of essentially new heterocyclic systems, by the successive treatment of available propargylamines with acyl chlorides (PdCl2/CuI/Ph3P/Et3N, toluene, 40-45 °C, 3 h) and sodium sulfide (Na2S·9H2O, EtOH, 20-25 °C, 7 h) has been developed. The synthesis comprises the addition of sulfide anions to the formed aminoacetylenic ketones followed by dehydrative cyclization of the prototropically rearranged adducts.

Sulfur-Promoted Oxidative Condensation of Chalcones with Unsubstituted Cyanoacetamide in DMSO: Access to 3-Cyanopyrid-2-ones

Elemental sulfur and DABCO were found to be an excellent combination to promote a one-pot cascade of condensation-oxidative cyclization of chalcones and unsubstituted cyanoacetamide in DMSO to provide 3-cyanopyrid-2-ones.

Fe/S-Catalyzed Redox Condensation of o-Nitrophenols with Isothiocyanates to 2-Aminobenzoxazoles

As frequently encountered byproducts of isocyanate chemistry, hydrogen sulfide and related sulfur containing compounds should be treated in a safe way to lower their adverse health and environmental effects, especially in large scale syntheses. As a proof of concept, we report herein an example of in situ recycling of sulfur byproduct to reductant in the synthesis of bioactive 2-aminobenzoxazoles 3. Using an Fe/S catalytic system, this heterocyclic scaffold could be obtained from o-nitrophenols 1 with isothiocyates 2 via direct redox condensation consisting of reduction of the nitro group of 1 by the sulfur moiety of 2.

Reaction of 1-acetonaphthones with anilines and elemental sulfur: rapid construction of 1-anilinonaphtho[2,1-b]thiophenes

1-Anilinonaphtho[2,1-b]thiophenes could be conveniently synthesized from a three-component reaction of 1-acetonaphthones with anilines and elemental sulfur under catalyst-free simple heating conditions.

The recent development of inverse vulcanized polysulfide as an alternative adsorbent for heavy metal removal in wastewater

Inverse vulcanized polysulfides have been used as low-cost and effective adsorbents to remediate heavy metals in wastewater. Inverse vulcanization introduces sustainable polysulfide synthesis by solving the rapid desulfurization problem of unstable polysulfides, and provides superior performance compared to conventional commercial adsorbents. The review discussed the brief applications of the inverse vulcanized polysulfides to remove heavy metal wastewater and emphasized the modified synthesis processes for enhanced uptake ratios. The characteristics of polysulfide adsorbents, which play a vital role during the removal process are highlighted with a proper discussion of the interaction between metal ions and polysulfides. The review paper concludes with remarks on the future outlook of these low-cost adsorbents with high selectivity to heavy metals. These polysulfide adsorbents can be prepared using a wide variety of crosslinker monomers including organic hydrocarbons, cooking oils, and agro-based waste materials. They have shown good surface area and excellent metal-binding capabilities compared to the commercially available adsorbents. Proper postmodification processes have enabled the benefits of repetitive uses of the polysulfide adsorbents. The improved surface area obtained by appropriate choice of crosslinkers, modified synthesis techniques, and regeneration through post-modification has made inverse vulcanized polysulfides capable of removing.

Base-catalyzed multicomponent access to quinoxalin-2-thiones from o-phenylenediamines, aryl ketones and sulfur

3-Arylquinoxaline-2-thiones were conveniently synthesized via three-component oxidative condensation of acetophenones with o-phenylenediamines and sulfur in DMSO in the presence of piperidine as a catalyst. The products could be readily isolated from the reaction mixture by simple precipitation and washing with methanol. This set of reaction conditions applied to higher homologs of acetophenones as well as benzyl phenyl ketones led to 2,3-di-C-substituted quinoxalines. Further functionalization of 3-phenylquinoxaline-2-thione via reaction on the thione group could be readily performed to provide quinoxaline derivatives in good yields.

DABCO-Catalyzed Reaction of 2-Naphthols with Aryl Isothiocyanates: Access to 2-Iminonaphtho-1,3-oxathioles

2-Naphthols 1 were found to react with aryl isothiocyanates 2 to provide 2-iminonaphtho-1,3-oxathioles 3 in the presence of DABCO as a catalyst. When elemental sulfur was used, moderate to good yields of 3 could be achieved from a nearly equimolar mixture of two starting materials 1 and 2. Products 3 could also be formed in the absence of sulfur or an external oxidant. In the latter case, an additional equivalent of 2 was found to act as a dehydrogenating agent.

Transition Metal-Free Iodine-Catalyzed Denitrative C-S Cross-Coupling: An Atypical Route to Access Thiochromane Derivatives

An iodine-catalyzed denitrative C-S cross-coupling reaction has been developed to attain thiochromanones from 2'-nitrochalcones and xanthate. The strategy was extended for a three-component synthesis of thiochromenes via intermolecular C-S cross-coupling followed by aldol reaction. The reaction proceeds via activation of the keto group of chalcone through a halogen bond complex with iodine/denitrative C-S bond formation with xanthate/sulfa-Michael addition to chalcones. The methodology was also demonstrated for chemoselective reduction of chalcones. The protocol was also employed to synthesize biologically important 3'-hydroxythioflavone and thiochromenones.

Convenient Synthesis of Triphenylphosphine Sulfide from Sulfur and Triphenylphosphine

Elemental sulfur (S8) was found to react very rapidly (<1 min) with a stoichiometric amount of triphenylphosphine at rt in sufficient amount of solvent (0.2–0.5 mL of solvent/1 mmol of PPh3). Compared to the previously described methods, the present procedure constitute excellent access to triphenylphosphine sulfide.

Direct Access to 2-Aryl-3-Cyanothiophenes by Base-Catalyzed One-pot Two-step Three-component Reaction of Chalcones with Benzoylacetonitriles and Elemental Sulfur

3-Cyanothiophene is an important heterocyclic scaffold in bioorganic and medicinal chemistry as a useful synthetic intermediate as well as in material sciences as a privilege motif for photovoltaic development. Herein,...

Double C-S bond formation via multiple Csp3-H bond cleavage: synthesis of 4-hydroxythiazoles from amides and elemental sulfur under metal-free conditions

A novel and efficient approach for the synthesis of 4-hydroxythiazoles from amides and elemental sulfur has been developed. In the presence of P₂O₅, DMSO and HMPA, this metal-free protocol proceeds smoothly and tolerates a spectrum of functional groups. Furthermore, this strategy involves the process of double Csp³-S bond formation through the cleavage of multiple Csp³-H bonds for the first time.

Fe/S-Catalyzed synthesis of 2-benzoylbenzoxazoles and 2-quinolylbenzoxazoles via redox condensation of o-nitrophenols with acetophenones and methylquinolines

An Fe/S catalyst generated in situ from FeCl₂·4H₂O and elemental sulfur S₈ in the presence of a tertiary amine as a base was found to catalyze efficiently a 6e^- redox condensation of o-nitrophenols with acetophenones and methylquinolines. The condensed products 2-benzoylbenzoxazoles and 2-quinolylbenzoxazoles were obtained in reasonable yields with water as the only byproduct at a temperature as low as 80 °C.

Base-Catalyzed Three-Component Reaction between Chalcones, Isothiocyanates, and Sulfur: Access to Thiazole-2-thiones

A convenient synthesis of thiazole-2-thiones was developed based on base-catalyzed three-component reactions between chalcones, isothiocyanates, and elemental sulfur.

Base-Catalyzed Three-Component Reaction of α-Cyanoacetates with Chalcones and Elemental Sulfur: Access to 2-Aminothiophenes Unobtainable via the Gewald Reaction

Although the Gewald reaction was well-known for more than half a century as an excellent method providing bioactive 2-aminothiophenes from reactions of α-cyanoacetates and carbonyl compounds and elemental sulfur, its application to dibenzoylmethanes as the carbonyl substrates was, however, unknown and experimentally proven unsuccessful. We propose here a convenient approach to such a series of compounds by a DABCO-catalyzed, one-pot, two-step, three-component reaction of α-cyanoacetate with chalcones and elemental sulfur. This catalytic strategy is highlighted by its excellent atom/step efficiency and high degree of structural diversification by simply choosing the suitable starting chalcones, which are unarguably much more readily available than dibenzoylmethanes.

Diiodine–Triethylsilane System: Reduction of N-Sulfonyl Aldimines to N-Alkylsulfonamides

Because molecular iodine and hydrosilanes are stable to both air and moisture, reactions using these reagents are easy to operate and require mild reaction conditions. Molecular iodine and a hydrosilane were used to reduce N-sulfonyl aldimines to the corresponding N-alkylsulfonamides. This transformation is a practical method for the synthesis of N-alkylsulfonamides.

Elemental Sulfur Mediated Novel Multicomponent Redox Polycondensation for the Synthesis of Alternating Copolymers Based on 2,4-Thiophene/Arene Repeating Units

A sulfur-based self-condensation method is investigated as an efficient tool for the synthesis of polythiophene derivatives. The reaction proceeds through multicomponent redox polycondensation between readily available diketone compounds and elemental sulfur in the presence of a Brønsted acid/base pair. Six different diketone derivatives have been screened and the polymerization is generalized by the synthesis of so-far-unprecedented alternating copolymers based on 2,4-thiophene/arene repeating units. By exploiting microwave heating the synthetic procedure is optimized, particularly for alternating copolymers containing aryl and thiophene units, such that a copolymer can be synthesized in only 24 h compared to the conventional process taking 6 d, yielding polymers within the same apparent weight average molar mass (M_w ). All obtained copolymers are analyzed in detail using size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), attenuated total reflectance infrared spectroscopy (ATR-IR), thermal gravimetric analysis and differential scanning calorimetry (DSC).

The catalytic role of elemental sulfur in the DMSO-promoted oxidative coupling of methylhetarenes with amines: synthesis of thioamides and bis-aza-heterocycles

The S₈/DMSO combination was found to be particularly effective to promote oxidative coupling of methylhetarenes with amines to synthesize thioamides/bis-aza-heterocycles.

ZnO nanoparticles supported on dendritic fibrous nanosilica as efficient catalysts for the one-pot synthesis of quinazoline-2,4(1H,3H)-diones

The transmutation of waste into valuable materials has a special place in green chemistry. Herein, we report the preparation of quinazoline-2,4(1H,3H)-diones from 2-iodoaniline, isocyanides, and carbon dioxide in the presence of ZnO NPs stably placed on the surface of dendritic fibrous nanosilica by cellulose (DFNS/cellulose-ZnO) as a catalyst. This is a great economic strategy to create three bonds in a one-pot multicomponent reaction step employing functional groups. To prepare the catalyst, the dendritic fibrous nanosilica surface was first activated using cellulose as a substrate to support ZnO NPs. Cellulose acts as a stabilizing and reducing agent for the ZnO nanocatalyst and eliminates the need for a reducing agent. The structure of the prepared DFNS/cellulose-ZnO was examined by various methods, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP). The largest amount of quinazoline-2,4(1H,3H)-diones was obtained under ideal situations in the presence of 5 mg of DFNS/cellulose-ZnO under carbon dioxide (1 atm) utilizing a balloon set at 70 °C for 3 hours. The substance was reused for ten consecutive runs and the quinazoline-2,4(1H,3H)-dione content was more than 92% each time. This indicates the potential for application in the green and economic production of quinazoline-2,4(1H,3H)-diones, especially from low-cost feedstocks.

The transmutation of waste into valuable materials has a special place in green chemistry.

Room-Temperature Synthesis of Tetrasubstituted 1,3-Dithioles by Dimerizing Sulfuration of Chalcones with Elemental Sulfur

Chalcones were found to undergo sulfurative dimerization with elemental sulfur to tetrasubstituted 1,3-dithioles. The reaction was found to proceed at room temperature in the presence of a nitrogen-base catalyst in DMSO.

Elemental-Sulfur-Incorporated Cyclizations of Pyrrolidines Leading to Thienopyrroles

We report, herein, the synthesis of thieno[3,2-b]pyrroles from the direct oxidative [4 + 1] cyclization of 2-alkynyl pyrrolidines with elemental sulfur. This transformation likely originates from electrophilic attack at the β-position of pyrrolidine followed by an intramolecular thienannulation to deliver the desired product. Mechanistic investigation suggests that the present reaction involves the formation of dihydrothieno[3,2-b]pyrrole as an intermediate.

Simultaneous biological nitrification and desulfurization treatment of ammonium and sulfide-rich wastewater: Effectiveness of a sequential batch operation

Sulfide inhibition to nitrifying bacteria has prevented the integration of digestate nitrification and biogas desulfurization to simplify anaerobic digestion systems. In this study, liquid digestate with NaHS solution was treated using nitrifying sludge in a sequential-batch reactor with a long fill period, with an ammonium loading rate of 293 mg-N L^-1 d^-1 and a stepwise increase in the sulfide loading rate from 0 to 32, 64, 128, and 256 mg-S L^-1 d^-1. Batch bioassays and microbial community analysis were also conducted with reactor sludge under each sulfide loading rate to quantify the microbial acclimatization to sulfide. In the reactor, sulfide was completely removed. Complete nitrification was maintained up to a sulfide load of 128 mg-S L^-1 d^-1, which is higher than that in previous reports and sufficient for biogas treatment. In the batch bioassays, the sulfide tolerance of NH₄⁺ oxidizing activity (the 50% inhibitory sulfide concentration) increased fourfold over time with the compositional shift of nitrifying bacteria to Nitrosomonas nitrosa and Nitrobacter spp. However, the sulfur removal rate of the sludge slightly decreased, although the abundance of the sulfur-oxidizing bacteria Hyphomicrobium increased by 30%. Therefore, nitrifying sludge was probably acclimatized to sulfide not by the increasing sulfide removal rate but rather by the increasing nitrifying bacteria, which have high sulfide tolerance. Successful simultaneous nitrification and desulfurization were achieved using a sequential-batch reactor with a long fill period, which was effective in facilitating the present acclimatization.