Iodide-Catalyzed Synthesis of Secondary Thiocarbamates from Isocyanides and Thiosulfonates

Cascade Reaction of Isocyanides with Carboxylic Acid and CD3SSO3Na: Toward S-CD3 Thiocarbamates

We developed an unprecedented cascade reaction involving isocyanides with carboxylic acids and CD3SSO3Na to access S-CD3 thiocarbamates with the formation of two C-N bonds and one C-S bond. Preliminary mechanistic investigations disclose that these three-component reactions precede the esterification of carboxylic acids with isocyanides, generating a capable N-alkyl-N-formyl amide followed by thiolation with CD3SSO3Na to provide the corresponding products. The transformation has outstanding features in mild reaction conditions, effortless experimental operation, structural modification of polyfunctional carboxylic acid drugs, and large-scale preparation.

Closing the Loop: Low-Waste Phosphorus Functionalization Enabled by Simple Disulfides

Useful monophosphorus products are obtained from both white and red phosphorus via a simple strategy involving initial oxidation by aryl disulfides followed by quenching with nucleophiles. Direct transformations of elemental phosphorus are usually very challenging, forcing chemists to instead rely on inefficient and hazardous multi-step methods. However, here they are achieved using inexpensive and easy-to-handle reagents, providing access to diverse P-C, P-N and P-O bonded products in good yields. By isolating the thiolate byproducts of these reactions, a simple, closed loop can be achieved that produces only minimal, benign waste byproducts, in contrast to other direct methods. This closed loop can even be elaborated into a true (electro)catalytic cycle, which is extremely rare in the field of elemental phosphorus functionalization.

Bifunctionalization of α-Bromophenone: An Access to Functionalized β-Keto Thiosulfones

A simple and high-yielding strategy to produce a variety of β-keto sulfides using asymmetrical and symmetrical thiosulfonates with ketones under mild conditions is reported. It was found that the various substituted compounds, with both electron-withdrawing and electron-donating substituents, afforded a wide range of β-keto thiosulfones (α-thioaryl-β-keto sulfones) in moderate to high yields. The transformations were reliable at the gram-scale, thus illustrating their efficiency and practicality. A plausible mechanism for the protocol is also proposed.

Cross-Electrophile Couplings of Benzyl Sulfonium Salts with Thiosulfonates via C-S Bond Activation

A zinc-mediated cross-electrophile coupling of benzyl sulfonium salts with thiosulfonates via C-S bond cleavage was achieved. The reductive thiolation proceeded well under transition metal-free conditions to afford the desired benzyl sulfides in good yields, exhibiting both broad substrate scope and good functionality tolerance. In addition, the reaction could be applied to the use of selenosulfonate as an effective selenylation agent and be subjected to scale-up synthesis.

Photo-induced decarboxylative C-S bond formation to access sterically hindered unsymmetric S-alkyl thiosulfonates and SS-alkyl thiosulfonates

Due to the high reactivity and versatility of benzenesulfonothioates, significant advancements have been made in constructing C-S bonds. However, there are certain limitations in the synthesis of S-thiosulfonates and SS-thiosulfonates, especially when dealing with substantial steric hindrance, which poses a significant challenge. Herein, we present an innovative approach for assembling unsymmetric S-thiosulfonates and unsymmetric SS-thiosulfonates through the integration of dual copper/photoredox catalysis. Moreover, we also realized the one-pot strategy by directly using carboxylic acids as raw materials by in-situ activation of them to access S-thiosulfonates and SS-thiosulfonates without further purification and presynthesis of NHPI esters. The envisaged synthesis and utilization of these reagents are poised to pioneer an innovative pathway for fabricating a versatile spectrum of mono-, di-, and polysulfide compounds. Furthermore, they introduce a class of potent sulfenylating reagents, empowering the synthesis of intricate unsymmetrical disulfides that were previously challenging to access.

Na2CO3-promoted synthesis of thiocarbamates from isocyanates and thiols under mild conditions

Here, we developed an efficient method for the synthesis of s-alkyl or aryl thiocarbamates catalyzed by Na2CO3 under mild conditions using alkyl or aryl isocyanates and thiophenols or thiols. In situ reaction with deuterated tetrahydrofuran (d8-THF) was carried out to investigate the reaction mechanism. This method has the advantages of high yield, good functional group tolerance and high atom economy.

Stabilized Carbon-Centered Radical-Mediated Carbosulfenylation of Styrenes: Modular Synthesis of Sulfur-Containing Glycine and Peptide Derivatives

Sulfur-containing amino acids and peptides play critical roles in organisms. Thiol-ene reactions between the thiol residues of L-cysteine and the alkenyl fragments in the designed coupling partners serve as primary tools for constructing C─S bonds in the synthesis of unnatural sulfur-containing amino acid derivatives. These reactions are favored due to the preference for hydrogen transfer from thiol to β-sulfanyl carbon radical intermediates. In this paper, the study proposes utilizing carbon-centered radicals stabilized by the capto-dative effect, generated under photocatalytic conditions from N-aryl glycine derivatives. The aim is to compete with the thiol hydrogen, enabling radical C─C bond formation with β-sulfanyl carbon radicals. This protocol is robust in the presence of air and water, offers significant potential as a modular and efficient platform for synthesizing sulfur-containing amino acids and modifying peptides, particularly with abundant disulfides and styrenes.

Electrochemically-driven difunctionalization of the isocyanide and Mumm rearrangement cascade: expeditious synthesis of N-acyl-N-alkyl S-thiocarbamates

We describe the novel electrochemical multicomponent reaction (e-MCR) of readily available isocyanides, thiols and carboxylic acids to form N-substituted S-thiocarbamate derivatives that are found in several biologically active compounds. The effectiveness of the μ-electro flow reactor (μ-EFR) was showcased through significant reduction in electrolyte volume during the reaction, achieving gram-scale production of 4a within a short 12 min residence time using a Pt/Pt flow cell.

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.

Protein-Templated Ugi Reactions versus In-Situ Ligation Screening: Two Roads to the Identification of SARS-CoV-2 Main Protease Inhibitors

Protein-templated fragment ligation was established as a method for the rapid identification of high affinity ligands, and multicomponent reactions (MCR) such as the Ugi four-component reaction (Ugi 4CR) have been efficient in the synthesis of drug candidates. Thus, the combination of both strategies should provide a powerful approach to drug discovery. Here, we investigate protein-templated Ugi 4CR quantitatively using a fluorescence-based enzyme assay, HPLC-QTOF mass spectrometry (MS), and native protein MS with SARS-CoV-2 main protease as template. Ugi reactions were analyzed in aqueous buffer at varying pH and fragment concentration. Potent inhibitors of the protease were formed in presence of the protein via Ugi 4CR together with Ugi three-component reaction (Ugi 3CR) products. Binding of inhibitors to the protease was confirmed by native MS and resulted in the dimerization of the protein target. Formation of Ugi products was, however, more efficient in the non-templated reaction, apparently due to interactions of the protein with the isocyanide and imine fragments. Consequently, in-situ ligation screening of Ugi 4CR products was identified as a superior approach to the discovery of SARS-CoV-2 protease inhibitors.

Stefano Marcaccini: a pioneer in isocyanide chemistry

Stefano Marcaccini was one of the pioneers in the use of isocyanide-based multicomponent reactions in organic synthesis. Throughout his career at the University of Florence he explored many different faces of isocyanide chemistry, especially those geared towards the synthesis of biologically relevant heterocycles. His work inspired many researchers who contributed to other important developments in the field of multicomponent reactions and created a school of synthetic chemists that continues today. In this manuscript we intend to review the articles on isocyanide multicomponent reactions published by Dr. Marcaccini and analyse their influence on the following works by other researchers. With this, we hope to highlight the immense contribution of Stefano Marcaccini to the development of isocyanide chemistry and modern organic synthesis as well as the influence of his research on future generations. We believe that this review will not only be a well-deserved tribute to the figure of Stefano Marcaccini, but will also serve as a useful inspiration for chemists working in this field.

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.

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.

Photoexcited sulfenylation of C(sp3)-H bonds in amides using thiosulfonates

A photoexcited sulfenylation of C(sp³)-H bonds in amides is developed for the synthesis of sulfenyl amides using thiosulfonates as a sulfur source. In the presence of easily available and inexpensive Na₂-eosin Y, TBHP and K₂CO₃, various sulfenyl amides can be obtained under the irradiation of blue light at room temperature.

The synthesis of anticancer sulfonated indolo[2,1-a]isoquinoline and benzimidazo[2,1-a]isoquinolin-6(5H)-ones derivatives via a free radical cascade pathway

A facile CuBr₂ induced radical relay addition/cyclization of activated alkenes with substituted-thiosulfonates has been achieved, leading to a broad range of sulfonated indolo[2,1-a]isoquinolines and benzimidazo[2,1-a]isoquinolin-6(5H)-ones in moderate to good yields. In particular, some compounds exhibit bioactivity against cancer cell lines. This protocol shows advantages of low-cost, base-free, simple operation, and broad functional group tolerance.

Synthesis and application of thiocarbamates via thiol-dioxazolone modified Lossen rearrangement

Thiocarbamates afforded from thiol-dioxazolone modified Lossen rearrangement under mild conditions were further applied to prepare polythiocarbamates with self-healing properties.

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.

Direct conversion of sulfinamides to thiosulfonates without the use of additional redox agents under metal-free conditions

Direct conversion of sulfinamides to thiosulfonates is described. Without the use of additional redox agents, the reaction proceeds smoothly in the presence of TFA under metal-free conditions. This protocol possesses many advantages such as odourless and stable starting materials, broad substrate scope, selective synthesis, and mild reaction conditions.

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.

Nickel-Catalyzed Reductive Thiolation of Unactivated Alkyl Bromides and Arenesulfonyl Cyanides

The cross-electrophile coupling between unactivated alkyl bromides with arenesulfonyl cyanides catalyzed by Ni(acac)₂ under reductive conditions to form unsymmetrical sulfides is developed. This approach for sulfide synthesis is practical, relies on available, unfunctionalized materials such as alkyl (pseudo)halides, and is scalable. This catalytic strategy provides a complementary method for the preparation of unsymmetrical alkyl-aryl sulfides under mild conditions with good functional group tolerance.

Metal-Free Radical Annulation of Oxygen-Containing 1,7-Enynes: Configuration-Selective Synthesis of (E)-3-((Arylsulfonyl)methyl)-4-Substituted Arylidenechromene Derivatives

A novel strategy for the synthesis of (E)-3-((arylsulfonyl)methyl)-4-substituted benzylidenechromene derivatives via a metal-free radical annulation reaction of oxygen-containing 1,7-enynes with thiosulfonates has been developed. The reaction shows broad substrate scope, wide functional group tolerance, and moderate to excellent yields. Moreover, thiosulfonates were well driven to achieve the bifunctionalization reaction of oxo-1,7-enynes which derived from aliphatic alkynes. In addition, the (E)-configuration of the products was highly controlled by the structure of 1,7-enyne.

Transition Metal-Free Synthesis of Carbamates Using CO2 as the Carbon Source

Utilization of carbon dioxide as a C1 synthon is highly attractive for the synthesis of valuable chemicals. However, activation of CO₂ is highly challenging, owing to its thermodynamic stability and kinetic inertness. With this in mind, several strategies have been developed for the generation of carbon-heteroatom bonds. Among these, formation of C-N bonds is highly attractive, especially, when carbamates can be synthesized directly from CO₂ . This Minireview focuses on transition metal-free approaches for the fixation of CO₂ to generate carbamates for the production of fine chemicals and pharmaceuticals. Within the past decade, transition metal-free approaches have gained increasing attention, but traditional reviews have rarely focused on these approaches. Direct comparisons between such methods have been even more scarce. This Minireview seeks to address this discrepancy.

Metal-Free Chemoselective Reaction of Sulfoxonium Ylides and Thiosulfonates: Diverse Synthesis of 1,4-Diketones, Aryl Sulfursulfoxonium Ylides, and β-Keto Thiosulfones Derivatives

A diverse chemoselective insertion reaction of sulfoxonium ylides and thiosulfonates under transition-metal-free conditions is developed, which successfully affords 1,4-diketone compounds, arylthiosulfoxide-ylides, and β-keto thiosulfones, respectively. The nucleophilic addition of two molecular sulfoxonium ylides to construct sulfone-substituted 1,4-dione compounds is the highlight of this work.

The same oxygenation-state introduction of hypervalent sulfur under transition-metal-free conditions

This review discusses the application of the same oxygenation-state introduction of hypervalent sulfur strategy under transition-metal-free conditions.

KI-catalyzed synthesis of S-Thiocarbamates by cross-coupling of cyclohexyl isocyanide with sulfonyl chlorides

A simple and efficient process for direct generation of various S-thiocarbamates is developed by cross-coupling of readily available sulfonyl chlorides with cyclohexyl isocyanide. The yields are excellent and the structures of the generated S-thiocarbamates are characterized by nuclear magnetic resonance spectroscopy, infrared spectroscopy, and high-resolution mass spectrometry together with X-ray crystallographic analysis. The protocol has the advantages of using easily available reagents, employs inexpensive KI as the reagent, demonstrates good functional group tolerance, and utilizes mild reaction conditions.

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

A general and efficient protocol for the direct preparation of various S-thiocarbamates with readily available and inexpensive sulfonyl chlorides as an odorless sulfur source was developed. The employment of easily available reactants, excellent functional group tolerability, and mild reaction conditions make this process very practical.

Synthesis of Functionalized Pyrazin-2(1 H)-ones via Tele-Nucleophilic Substitution of Hydrogen Involving Grignard Reactants and Electrophiles

The reaction of 6-chloro-1-methylpyrazin-2(1 H)-one with Grignard reactants followed by quenching with different electrophiles gave access to a variety of 3,6-difunctionalized 1-methylpyrazin-2(1 H)-ones. This regioselective three-component reaction represents the first example of a tele-nucleophilic substitution of hydrogen (S_N^H) in which the anionic σ^H adduct is quenched by electrophiles (other than a proton) before elimination takes place. Quenching the reaction with iodine (I₂) or bromine (Br₂) provides an alternative reaction pathway, yielding a 3-functionalized 6-chloro-1-methylpyrazin-2(1 H)-one or 5-bromo-6-chloro-1-methylpyrazin-2(1 H)-one, respectively. The halogens present offer opportunities for further selective transformations.

Metal-Free Catalytic Synthesis of Thiocarbamates Using Sodium Sulfinates as the Sulfur Source

A novel molecular iodine-catalyzed protocol for the construction of thiocarbamates from readily available sodium sulfinates, isocyanides, and water has been described. The present methodology offers a facile and practical route to a variety of thiocarbamates in moderate to good yields with favorable functional group tolerance by use odorless sodium sulfinates as the sulfur source. The mechanistic studies suggest the present transformation involves a radical process.

Metal-free NaI/TBHP-mediated sulfonylation of thiols with sulfonyl hydrazides

A highly efficient sulfonylation of thiols has been achieved through the metal-free NaI/TBHP-mediated cross-coupling of sulfonyl hydrazides and thiols at room temperature. This method provides a convenient and practical route to thiosulfonates in 84-99% yields (39 examples) with wide functional group compatibility.