Iodine-Catalyzed Odorless Synthesis of S-Thiocarbamates with Sulfonyl Chlorides as a Sulfur Source

Direct C-H Sulfuration: Synthesis of Disulfides, Dithiocarbamates, Xanthates, Thiocarbamates and Thiocarbonates

In light of the important biological activities and widespread applications of organic disulfides, dithiocarbamates, xanthates, thiocarbamates and thiocarbonates, the continual persuit of efficient methods for their synthesis remains crucial. Traditionally, the preparation of such compounds heavily relied on intricate multi-step syntheses and the use of highly prefunctionalized starting materials. Over the past two decades, the direct sulfuration of C-H bonds has evolved into a straightforward, atom- and step-economical method for the preparation of organosulfur compounds. This review aims to provide an up-to-date discussion on direct C-H disulfuration, dithiocarbamation, xanthylation, thiocarbamation and thiocarbonation, with a special focus on describing scopes and mechanistic aspects. Moreover, the synthetic limitations and applications of some of these methodologies, along with the key unsolved challenges to be addressed in the future are also discussed. The majority of examples covered in this review are accomplished via metal-free, photochemical or electrochemical approaches, which are in alignment with the overraching objectives of green and sustainable chemistry. This comprehensive review aims to consolidate recent advancements, providing valuable insights into the dynamic landscape of efficient and sustainable synthetic strategies for these crucial classes of organosulfur compounds.

Tunable Regioselective Allylic Alkylation/Iodination of Imidazoheterocycles in Water

The switchable roles of allylic alcohol and molecular iodine as reagents and catalysts have been demonstrated in the regioselective allylic alkylation and iodination of imidazoheterocycles employing the mixture of allylic alcohol-I2. First, we have explored the catalytic activity of iodine for the allylation of imidazoheterocycles using allylic alcohol in an aqueous medium. The allylation of a library of imidazoheterocycles and other electron-rich heterocycles like indole, pyrazole, 4-hydroxy coumarin, and 6-amino uracil has been achieved by employing this methodology. The efficiency of the I2 catalyst for N-allylation of azoles has also been demonstrated. Next, we have shown that this mixture of allylic alcohol and I2 could be beneficial for the iodination of imidazoheterocycles under room temperature. Mechanistic studies indicate that the activation of allylic alcohol by molecular iodine took place probably through halogen bonding, and NMR studies show that the reaction did not proceed through allylic ether formation.

S-alkyl Dithiocarbamates Synthesis through Electrochemical Multicomponent Reaction of Thiols, Hydrogen Sulfide, and Isocyanides

Dithiocarbamates synthesis is extremely important in plenty of biomedical and agrochemical applications, especially fungicide development, but remains a great challenge. In this work, we have successfully developed a multicomponent reaction protocol to convert H2S into S-alkyl dithiocarbamates under constant current conditions. No additional oxidants nor additional catalysts are required, and due to mild conditions, the reactions display a broad substrate scope, including varieties of thiols or disulfides.

Organophosphorus-Catalyzed "Dual-Substrate Deoxygenation" Strategy for C-S Bond Formation from Sulfonyl Chlorides and Alcohols/Acids

A green method to construct C-S bonds using sulfonyl chlorides and alcohols/acids via a P^III/P^V═O catalytic system is reported. The organophosphorus-catalyzed umpolung reaction promotes us to propose the "dual-substrate deoxygenation" strategy. Herein, we adopt the "dual-substrate deoxygenation" strategy, which achieves the deoxygenation of sulfonyl chlorides and alcohols/acids to synthesize thioethers/thioesters driven by P^III/P^V═O redox cycling. The catalytic method represents an operationally simple approach using stable phosphine oxide as a precatalyst and shows broad functional group tolerance. The potential application of this protocol is demonstrated by the late-stage diversification of drug analogues.

Recent Advances in the Electrochemical Functionalization of Isocyanides

Isocyanides are well-known as efficient CO surrogates and C1 synthons in modern organic synthesis. Although tremendous efforts have been devoted to fully exploiting the reactivity of isocyanides, these transformations are primarily limited by their utilization of stoichiometric toxic chemical oxidants. With the recent resurgence of organic electrochemistry, which has considerably laid dormant over the past several decades, electrolysis has been identified as a green and powerful tool to enrich structural diversity by solely utilizing electric current as clean and inherently safe redox equivalents of stoichiometric chemical oxidants. In this regard, the unique reactivity of isocyanides has been studied in numerous electrochemical transformations. This review comprehensively highlights the most relevant progress in electrochemical strategies towards the functionalization of isocyanides up until June of 2022, with a focus on reaction outcomes and mechanisms.

Synthetic and computational investigation of neighboring group participation by a nucleophilic disulfide bond

Disulfide bonds of 2-isocyanatophenyl methyl disulfide and 2-endo-isocyanato-6-endo-(methyldisulfanyl)bicyclo[2.2.1]heptane showed neighboring group participation in the formation of thiocarbamates. Natural Bond Orbital (NBO) analyses revealed that the unusual nucleophilicity requires a rigid through-space interaction between a lone pair of the disulfide bond and an antibonding orbital of isocyanate.

Modulating Carrier Transfer over Carbazolic Conjugated Microporous Polymers via Donor Structural Design for Functionalization of Thiophenols

Developing photocatalysts to steer conversion of solar energy toward high-value-added fine chemicals represents a potentially viable approach to address the energy crisis and environmental issues. However, enablement of this conversion is usually impeded by the sluggish kinetic process for proton-coupled electron transfer and rapid recombination of photogenerated excitons. Herein, we report a simple and general structural expansion strategy to facilitate charge transfer in conjugated microporous polymers (CMPs) via engineering the donor surrounding the trifluoromethylphenyl core. The resulting CMPs combine high surface area, strong light-harvesting capabilities, and tunable optical properties endowed by extended π-conjugation; the optimized compound CbzCMP-5 generated from 9,9',9″-(2-(trifluoromethyl)benzene-1,3,5-triyl)tris(9H-carbazole) remarkably enhanced the photogenerated carrier transfer efficiency, enabling the functionalization of thiophenols toward thiocarbamates and 3-sulfenylindoles with high photocatalytic efficiency. Most importantly, the in-depth insights into the carrier-transfer processes open up new prospects on further optimization and rational design of photoactive polymers for efficient charge-transfer-mediated reactions.

Electrosynthesis of S-thiocarbamates with disulfides as a sulfur source

An electrochemical oxidative synthesis of S-thiocarbamates by a carbamothioation reaction via a three-component coupling reaction (disulfide, water and isocyanide) is developed, which avoids the use of external oxidants and generates only hydrogen gas as the by-product. With NH₄I as the mediator and electrolyte, the desired S-thiocarbamates were obtained in good yields in an undivided cell at room temperature.

Electrochemical metal- and oxidant-free synthesis of S-thiocarbamates

An expeditious synthetic strategy to access functionalized S-thiocarbamates was developed in good to excellent yields and with high current efficiencies. Readily available isocyanides and thiols were used as the starting materials under simple metal- and oxidant-free reaction conditions avoiding an inert atmosphere. The practical application of the present methodology was achieved by electrochemical synthesis of the herbicides prosulfocarb and pebulate. Furthermore, continuous electrochemical flow conditions using a graphite/Pt flow cell were used to obtain S-thiocarbamate compounds on a gram scale within a residence time of 35 min.

Visible-light-promoted synthesis of secondary and tertiary thiocarbamates from thiosulfonates and N-substituted formamides

A general visible-light-promoted metal-free synthesis of secondary and tertiary thiocarbamates starting from thiosulfonates and N-substituted formamides is developed. By employing rhodamine B as a photocatalyst and tert-butyl hydroperoxide (TBHP) as an oxidant, a wide scope of thiocarbamates can be obtained through direct thiolation of acyl C-H bonds under irradiation of blue light at room temperature for 12 h.

Sustainable Four-Component Annulation for the Synthesis of 2,3,4,6-Tetraarylpyridines

A one-pot, four-component annulation of 2,3,4,6-tetraarylpyridines from aromatic aldehydes, methyl ketones, diaryl ethanones, and ammonium acetate is described. The reaction features high functional group compatibility in air under solvent-free conditions without any additive and only water as the nontoxic byproduct, providing a strategy for the facile, economical, and eco-friendly construction of multiaryl-substituted pyridines from simple and readily available reactants.

Revisiting applications of molecular iodine in organic synthesis

Molecular iodine contributes significantly to organic transformations in synthetic organic chemistry. It works effectively due to its mild Lewis acidic character, ability as an oxidizing agent, good moisture stability, and easy availability.

Metal-free electrochemical synthesis of α-ketoamides via decarboxylative coupling of α-keto acids with isocyanides and water

A mild and convenient electrochemical protocol has been developed for the preparation of α-ketoamides via a decarboxylative coupling reaction of α-keto acids with isocyanides and water.

Autocatalytic deoximation reactions driven by visible light

Photocatalytic deoximation reaction was found to be an autocatalytic process that occurs via free-radical mechanism. Understanding the mechanism may help chemical engineers to develop related techniques to avoid the decomposition of oximes.

Stereoselective synthesis of fully substituted ethylenes via an Ag-catalyzed 1,6-nucleophilic addition/annulation cascade

A catalytic 1,6-nucleophilic addition/annulation cascade was developed for the first time, and used to produce 27 hitherto unreported ethylene-linked 1-naphthol-imidazole pairs with generally good yields and complete stereoselectivity. An Ag₂O-catalyzed reaction of yne-allenone esters with tosylmethyl isocyanide proceeded efficiently, and provided a simple and convergent protocol for the synthesis of fully substituted (Z)-ethylenes whereas tetrasubstituted (E)-ethylenes were obtained when ethyl isocyanoacetate was employed in this transformation. The reaction pathway consists of [2+2] cycloaddition, 1,6-nucleophilic addition and [3+2] cycloaddition, leading to continuous multiple bond-forming events including C-C and C-N bonds to construct complex molecules.

Synthesis of unsymmetrical disulfides via PPh3-mediated reductive coupling of thiophenols with sulfonyl chlorides

A facile and rapid synthesis of unsymmetrical aryl disulfides using PPh3-mediated reductive coupling of thiophenols with aryl sulfonyl chlorides was described. Good functional group tolerance and scalability were achieved in this strategy. More importantly, the approach enables the introduction of sulfonyl chlorides into the synthesis of asymmetric organic disulfides under catalyst- and base-free conditions. Using this method, unsymmetrical aromatic disulfides could be prepared from inexpensive and readily available starting materials in moderate to excellent isolated yields, through a nucleophilic substitution pathway.

Direct cyanation, hydrocyanation, dicyanation and cyanofunctionalization of alkynes

In this review, direct cyanation, hydrocyanation, dicyanation, cyanofunctionalization and other cyanation reactions of alkynes were highlighted. Firstly, the use of nitriles and development of cyanation was simply introduced. After presenting the natural properties of alkynes, cyanation reactions of alkynes were classified and introduced in detail. Transition metal catalysed direct cyanation and hydrocyanation of alkynes gave alkynyl cyanides and alkenyl nitriles in good yields. Dicyanation of alkynes produced 1,2-dicyano adducts. Cyanofunctionalization of alkynes afforded functional cyanated compounds. Thiocyanation and selenocyanation yielded the expected functional vinylthiocyanates and vinylselenocyanates. A plausible reaction mechanism is presented if available.

ZnO-nanorods Promoted Synthesis of α-amino Nitrile Benzofuran Derivatives using One-pot Multicomponent Reaction of Isocyanides

AIMS AND OBJECTIVE

In this work ZnO-nanorod (ZnO-NR) as reusable catalyst promoted Strecker-type reaction of 2,4-dihydroxyacetophenone, isopropenylacetylene, trimethylsilyl cyanide (TMSCN), primary amines and isocyanides at ambient temperature under solvent-free conditions and produced α-amino nitriles benzofuran derivatives in high yields. These synthesized compounds may have antioxidant ability.

MATERIALS AND METHODS

ZnO-NRs in these reactions were prepared according to reported article. 2,4-dihydroxyacetophenone 1 (2 mmol) and isopropenylacetylene 2 (2 mmol) were mixed and stirred for 30 min in the presence of ZnO-NR (10 mol%) under solvent-free conditions at room temperature. After 30 min, primary amine 3 (2 mmol) was added to the mixture gently and the mixture was stirred for 15 min. After this time TMSCN 4 (2 mmol) was added to the mixture and stirred for 15 min. After completion of the reaction, as indicated by TLC, isocyanides 5 was added to mixture in the presence of catalyst.

RESULTS

In the first step of this research, the reaction of 2,4-dihydroxyacetophenone 1, isopropenylacetylene 2, methyl amine 3a, trimethylsilyle cyanide 4 and tert-butyl isocyanides 5a was used as a sample reaction to attain the best reaction conditions. The results showed this reaction performed with catalyst and did not have any product without catalyst after 12 h.

CONCLUSION

In conclusion, we investigate multicomponent reaction of 2,4-dihydroxyacetophenone 1, isopropenylacetylene 2, primary amines 3, trimethylsilyl cyanide 4 and isocyanides along with ZnO-NRs as reusable catalyst at room temperature under solvent-free conditions which generates α-amino nitrile benzofuran derivatives in high yields. The advantages of our method are high atom economy, green reaction conditions, higher yield, shorter reaction times, and easy work-up, which are in good agreement with some principles of green chemistry. The compounds 8c exhibit excellent DPPH radical scavenging activity and FRAP compared to synthetic antioxidants BHT and TBHQ.

Selenium-catalyzed oxidation of alkenes: insight into the mechanisms and developing trend

Recent progresses of the selenium-catalyzed oxidation of alkenes are summarized at the mechanism level. It may be beneficial for designing novel selenium-containing catalysts and alkene oxidation protocols for the next phase of studies.

Synthesis of benzonaphthofuroquinones and benzoylnaphthindolizinediones by reactions of flavonoids with dichlone under basylous, oxygenous and aqueous conditions: their cytotoxic and apoptotic activities

Using flavonoids and dichlone as substrates, six benzonaphthofuroquinones and three benzoylnaphthindolizinediones were synthesized through common base-catalyzed method and a new method of combining base-catalyzed with O₂/H₂O exposing.

Stereoselective synthesis of trans-aziridines via intramolecular oxidative C(sp3)–H amination of β-amino ketones

An expedient strategy for the synthesis of trans-2,3-disubstituted via the intramolecular KI/TBHP mediated oxidative dehydrogenative C(sp³)–H amination reaction was presented.

Iodine-catalyzed convergent aerobic dehydro-aromatization toward benzazoles and benzazines

An iodine-catalyzed aerobic dehydro-aromatization has been developed, providing straightforward and efficient access to various benzoazoles and benzoazines. The present transition-metal-free protocol enables the dehydro-aromatization of tetrahydrobenzazoles and tetrahydroquinolines with molecular oxygen as the green oxidant, along with some other N-heterocycles. Hence, a broad range of heteroaromatic compounds are generated in moderate to good yields under facile reaction conditions.

An iodine-catalyzed aerobic dehydro-aromatization has been developed, providing a straightforward and efficient access to various benzoazoles and benzoazines.

Access to 1-amino-3,4-dihydroisoquinolines via palladium-catalyzed C-H bond aminoimidoylation reaction from functionalized isocyanides

Efficient access to 1-amino-3,4-dihydroisoquinolines, through palladium-catalyzed intramolecular C-H bond aminoimidoylation of α-benzyl-α-isocyanoacetates, has been developed. Consecutive isocyanide insertion and C-H bond activation were realized with C-N and C-C bonds formation in one step under redox neutral conditions, employing O-benzoyl hydroxylamines as electrophilic amino sources.

Iron(0)-Mediated Reformatsky Reaction for the Synthesis of β-Hydroxyl Carbonyl Compounds

An efficient, economical, and practical Reformatsky reaction of α-halo carbonyl compounds with aldehydes/ketones by using cheap and commercial iron(0) powder as reaction mediator is developed. The reactions proceeded effectively in the presence of a catalytic amount of iodine (20 mol %) to afford the synthetically useful β-hydroxyl carbonyl compounds in moderate to good yields.

Efficient non-aqueous solvent formed by 2-piperidineethanol and ethylene glycol for CO2 absorption

CO₂ directly reacts with ethylene glycol by forming a carbonate species in the solvent consisting of 2-piperidineethanol and ethylene glycol.

Silver-mediated oxidative 1,2-alkylesterification of styrenes with nitriles and acids via C(sp3)–H functionalization

A new silver-mediated 1,2-alkylesterification of alkenes with nitriles and acids promoted by a catalytic amount of nickel catalyst for producing acyloxylated nitriles has been developed via a C(sp³)–H functionalization process.