Thiocarbonyl Surrogate via Combination of Potassium Sulfide and Chloroform for Dithiocarbamate Construction

Conversion of Acids to S-Alkyl Dithiocarbamates by Decarboxylative Sulfuration Using Visible-Light Photocatalysis

S-Alkyl dithiocarbamates, as an important class of sulfur-containing compounds, play pivotal roles in diverse fields, yet methods for the synthesis that start from simple, readily available feedstocks and exhibit mild conditions and structurally diverse products are scarce. In this work, we developed an efficient approach for the synthesis of various S-alkyl dithiocarbamates via visible-light photocatalysis with readily available and structurally diverse alkyl carboxylic acids (primary, secondary, and tertiary acids, amino acids, etc.) and disulfide tetraalkylthiuram as the starting materials. This protocol features high efficiency, mild reaction conditions, a broad substrate scope, and good functional group tolerance. Potential applications are further demonstrated by a sunlight experiment, H2O as a solvent, gram-scale synthesis, and facile synthesis of bioactive molecules.

Synthesis of Unsymmetrical Trisulfides from S-Substituted Sulphenylthiosulphates

Trisulfide unit is widely found in natural products and has garnered attention due to the unique pharmacological and physiochemical properties. However, despite limited progress, widely applicable approaches for constructing unsymmetrical trisulfides have so far remain scarce. In this work, an easy-to-prepare, solid-state and scalable reagent, S-substituted sulphenylthiosulphate, has been developed for the divergent synthesis of unsymmetrical trisulfides. Alkyl electrophile substrates, including bromides, chlorides, iodides and tosylates, with diverse substituents are smoothly converted to the corresponding trisulfides with S-substituted sulphenylthiosulphates and thiourea as another sulfur source. Furthermore, the late-stage modification of drug molecules was successfully achieved through this method.

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.

Base-mediated synthesis of cyclic dithiocarbamates from 1-amino-3-chloropropan-2-ol derivatives and carbon disulfide

An efficient method for the preparation of six-membered cyclic dithiocarbamates is described, in which triethylamine effectively promotes the reaction of 1-amino-3-chloropropan-2-ol derivatives with carbon disulfide. On the basis of the experimental and theoretical studies, a reaction mechanism is proposed to explain the difference between the present reaction and our previously reported carbon dioxide fixation.

Nitroalkanes as thioacyl equivalents to access thioamides and thiopeptides

Thioamides are an important, but a largely underexplored class of amide bioisostere in peptides. Replacement of oxoamide units with thioamides in peptide therapeutics is a valuable tactic to improve biological activity and resistance to enzymatic hydrolysis. This tactic, however, has been hampered by insufficient methods to introduce thioamide bonds into peptide or protein backbones in a site-specific and stereo-retentive fashion. In this work, we developed an efficient and mild thioacylation method to react nitroalkanes with amines directly in the presence of elemental sulfur and sodium sulfide to form a diverse range of thioamides in high yields. Notably, this convenient method can be employed for the controlled thioamide coupling of multifunctionalized peptides without epimerization of stereocenters, including the late stage thioacylation of advanced compounds of biological and medicinal interest. Experimental interrogation of postulated mechanisms currently supports the intermediacy of thioacyl species.

Nickel-Catalyzed Amidation of Aryl Alkynyl Acids with Tetraalkylthiuram Disulfides: A Facile Synthesis of Aryl Alkynyl Amides

Nickel-catalyzed amidation of aryl alkynyl acids using tetraalkylthiuram disulfides as the amine source is described, affording a series of aryl alkynyl amides in good to excellent yields under mild conditions. This general methodology provides an alternative pathway for the synthesis of useful aryl alkynyl amides in an operationally simple manner, which shows its practical synthetic value in organic synthesis. The mechanism of this transformation was explored through control experiments and DFT calculations.

Efficient Construction of Symmetrical Diaryl Sulfides via a Supported Pd Nanocatalyst-Catalyzed C-S Coupling Reaction

Aryl sulfides play an important role in pharmaceuticals, biologically active molecules and polymeric materials. Herein, a general and efficient protocol for Pd@COF-TB (a kind of Pd nanocatalyst supported by a covalent organic framework)/DIPEA-catalyzed one-pot synthesis of symmetrical diaryl sulfides through a C-S coupling reaction from aryl iodides and Na₂S₂O₃ is developed. More importantly, the addition of N,N-diisopropylethylamine (DIPEA) can not only enhance the catalytic activity of a Pd@COF-TB nanocatalyst, but also effectively inhibit the formation of biphenyl byproducts, which are a product of Ullmann reaction. Besides, it has been confirmed that the aryl Bunte salts generated in situ from Na₂S₂O₃ and aryl iodides are the sulfur sources involved in this C-S coupling reaction. With the strategy proposed in this work, a variety of symmetrical diaryl sulfides could be obtained in moderate to excellent yields with a high tolerance of various functional groups. Moreover, a possible mechanism of this Pd nanoparticle-catalyzed C-S coupling reaction is proposed based on the results of controlling experiments.

Ynamide-Mediated Thioamide and Primary Thioamide Syntheses

Environmentally friendly ynamide-mediated thioamidation of monothiocarboxylic acids with amines or ammonium hydroxide for the syntheses of thioamides and primary thioamides is described. Simple and mild reaction conditions enable the reaction to tolerate a wide variety of functional groups such as hydroxyl group, ester, tertiary amine, ketone, and amide moieties. Readily available NaSH served as the sulfur source, avoiding the use of toxic, expensive, and malodorous organic sulfur reagents and making this strategy environmentally friendly and practical. Importantly, the stereochemical integrity of α-chiral monothiocarboxylic acids was maintained during the activation step and subsequent aminolysis process, thus offering a racemization-free strategy for peptide C-terminal modification. Furthermore, a number of thioamide-modified drugs were prepared in good yields by using this protocol and the synthesized primary thioamides were transformed into backbone thiazolyl modified peptides.

Non-Hydroxamate Zinc-Binding Groups as Warheads for Histone Deacetylases

Histone deacetylases (HDACs) remove acetyl groups from acetylated lysine residues and have a large variety of substrates and interaction partners. Therefore, it is not surprising that HDACs are involved in many diseases. Most inhibitors of zinc-dependent HDACs (HDACis) including approved drugs contain a hydroxamate as a zinc-binding group (ZBG), which is by far the biggest contributor to affinity, while chemical variation of the residual molecule is exploited to create more or less selectivity against HDAC isozymes or other metalloproteins. Hydroxamates have a propensity for nonspecificity and have recently come under considerable suspicion because of potential mutagenicity. Therefore, there are significant concerns when applying hydroxamate-containing compounds as therapeutics in chronic diseases beyond oncology due to unwanted toxic side effects. In the last years, several alternative ZBGs have been developed, which can replace the critical hydroxamate group in HDACis, while preserving high potency. Moreover, these compounds can be developed into highly selective inhibitors. This review aims at providing an overview of the progress in the field of non-hydroxamic HDACis in the time period from 2015 to present. Formally, ZBGs are clustered according to their binding mode and structural similarity to provide qualitative assessments and predictions based on available structural information.

Visible-Light-Induced Photocatalytic Synthesis of β-Keto Dithiocarbamates via Difunctionalization of Styrenes

A facile photocatalyzed strategy for difunctionalization of styrenes in the presence of CS₂ and amines providing β-keto dithiocarbamates has been developed. In the case of 4-nitrostyrene and 2-vinylpyridine, however, only 2-arylethylthiocarbamates are interestingly formed without the aid of photoredox catalysis/TBHP.

A chromatography-free and aqueous waste-free process for thioamide preparation with Lawesson's reagent

After completing the thio-substitution with Lawesson’s reagent, ethanol was found to be effective in the decomposition of the inherent stoichiometric six-membered-ring byproduct from the Lawesson’s reagent to a highly polarized diethyl thiophosphonate. The treatment significantly simplified the following chromatography purification of the desired thioamide in a small scale preparation. As scaling up the preparation of two pincer-type thioamides, we have successfully developed a convenient process with ethylene glycol to replace ethanol during the workup, including a traditional phase separation, extraction, and recrystallization. The newly developed chromatography-free procedure did not generate P-containing aqueous waste, and only organic effluents were discharged. It is believed that the optimized procedure offers the great opportunity of applying the Lawesson’s reagent for various thio-substitution reactions on a large scale.

Synthesis of 1,3,4-Thiadiazoles and 1,4,2-Oxathiazoles from α-Enolic Dithioesters and Active 1,3-Dipoles

The synthesis of two kinds of five-membered organosulfur heterocycles (i.e., 1,4,2-oxathiazoles and 1,3,4-thiadiazoles) from α-enolic dithioesters with active 1,3-dipoles (nitrile oxides and nitrilimines) generated in situ was achieved under mild reaction conditions. This transformation further expands the synthetic application of α-enolic dithioesters as the sulfur-containing building blocks.

One-pot four-component assembly for diselenocarbamates

A one-pot four-component synthesis of diselenocarbamates was established from the combination of diselanes, selenium powder, chloroform and amines under mild conditions.

A Concise Approach to N-Substituted Rhodanines through a Base-Assisted One-Pot Coupling and Cyclization Process

An efficient approach to obtain functionalized rhodanines was developed through a base-assisted one-pot coupling and continuous cyclization of a primary amine, carbon disulfide, and methyl (2-chloroacetyl)carbamate. This conversion tolerates a broad range of functional groups and can be used to scale the preparation of N-substituted rhodanines in excellent yields.