One-Pot Synthesis of Difluoromethyl Thioethers from Thiourea and Diethyl Bromodifluoromethylphosphonate

Thiourea Derivatives in Agrochemical Discovery and Development

Thiourea, represented by the chemical formula (R1R2N)(R3R4N)C═S, is a significant organic sulfur compound characterized by the presence of a sulfur atom and two amino groups. Meanwhile, thiourea and isothiourea are reciprocal isomers. This structure facilitates the formation of a biologically active moiety, which is interconnected through double bonds between the sulfur atom and the nitrogen atoms. As a potent component in pesticide formulations, thiourea demonstrates efficacy in safeguarding crops against a variety of diseases by inhibiting the growth and reproduction of pathogens. This review aims to provide a comprehensive summary of thiourea derivatives exhibiting fungicidal, insecticidal, antiviral, herbicidal, and plant growth regulatory properties, with the objective of offering new perspectives for identifying innovative thiourea-based pesticides and elucidating their mechanisms of action.

Recent Advances of C-S Coupling Reaction of (Hetero)Arenes by C-H Functionalization

Organic sulfur compounds encompass a vast and diverse variety of species that possess unique biological activity due to the presence of sulfur atoms or sulfur-containing functional groups. These compounds are widely present in natural products, pharmaceuticals, agricultural chemicals, and functional materials. In recent years, numerous sulfur-containing compounds such as thiols, thioethers, disulfides, thiourea, dimethyl sulfoxide, sulfonates and their derivatives, as well as sulfur-containing inorganic compounds, have been utilized as coupling agents to synthesize (hetero)aryl sulfides via C-H Functionalization. These novel transformations provide effective methods for constructing C-S bond of (hetero)arenes, while also expanding the scope of (hetero)aryl sulfides with the potential biological activity. Therefore, the synthesis of aryl sulfides through C-H bond functionalization has attracted widespread attention. This review mainly focuses on the construction of (hetero)aryl sulfides via C-H bond functionalization since 2015. We hope this review offers a useful conceptual overview and inspires further advancements in the efficient construction of C-S bonds.

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.

Intramolecular Heterocyclization/Fluoromethylthiolation of Alkynes Enabled by a Multicomponent Reagent System

The BnSR_f (R_f = CF₂H or CF₃)/mCPBA/Tf₂O system was found to be an effective multicomponent reagent system for the one-pot synthesis of di/trifluoromethylthiolated heterocycles from alkynes. The reaction was postulated to proceed via a cascade sequence involving the oxidation of BnSR_f by mCPBA, activation of the in situ-generated sulfoxide by Tf₂O, and intramolecular cyclization/fluoromethylthiolation of the alkyne substrates enabled by the formed electrophilic sulfonium salt to give di/trifluoromethylthiolated heterocycles.

HCF2Se/HCF2S Installation by Tandem Substitutions from Alkyl Bromides

Herein we describe an efficient construction of HCF₂Se and HCF₂S groups by tandem substitutions between alkyl bromides and a reagent system consisting of MSeCN (or MSCN) and Ph₃P⁺CF₂H Br^-. The tandem process occurs via the first nucleophilic substitution of alkyl bromides by -SeCN (or -SCN) and the subsequent nucleophilic difluoromethylation.

Slicing and Splicing of Bromodifluoro-N-arylacetamides: Dearomatization and Difunctionalization of Pyridines

Copper-catalyzed dearomatization and difunctionalization of pyridines have been disclosed, in which bromodifluoro-N-arylacetamide was sliced into five fragments and three or four of them were transferred to pyridine partners. Through this reaction, novel N-difluoromethyl-2-imine dihydropyridine derivatives can be conveniently accessed from commercially available 4-amino substituted pyridines. This strategy demonstrates a novel fluorination method featuring high atom economy, environmental friendliness, an easily available catalyst, and simple operation.

Diastereoselective and Reversed Regioselective Annulations of N-Alkyl Anilines to Julolidines and Lilolidines

A three-component annulation reaction of N-alkyl anilines, cyclic 1,3-dicarbonyl compounds, and aryl aldehydes to julolidines and lilolidines is reported. The 6π-electrocyclization enabled the annulation to proceed with reversed regioselectivity as compared with the annulation that occurs in the Povarov reaction. Both cyclic and acyclic N-alkyl anilines participated in the reaction to provide a wide range of julolidines and lilolidines as the single regio- and diastereoisomers in good to excellent yields.

Synthesis of difluoromethyl and deuterium-labeled difluoromethyl thioethers from aliphatic electrophiles

A one-pot difluoromethylthiolation of alkyl electrophiles with thiourea and diethyl bromodifluoromethylphosphonate is described. The transition-metal-free approach, readily available reagents, and mild conditions provide a practical way for the synthesis of difluoromethyl thioethers. By changing the "H" source to the most commonly used "D" sources CD₃OD and D₂O, this strategy enables efficient synthesis of SCF₂D-substituted molecules in good yields with high levels of D incorporation.

Exploration of new reaction tools for late-stage functionalization of complex chemicals

Chemistry has always had as a target the conversion of molecules into valuable materials. Nevertheless, the aim of past synthesis has primarily focused on achieving a given transformation, regardless of the environmental impact of the synthetic route. Given the current global situation, the demand for sustainable alternatives has substantially increased. Our group focuses on developing selective chemical transformations that benefit from mild conditions, improved atom economy, and that can make use of renewable feedstocks as starting materials. This account summarizes our work over the past two decades specifically regarding the selective removal, conversion, and addition of functional groups that can, later on, be applied at a late stage for the modification of complex molecules.

Cesium carbonate-promoted synthesis of aryl methyl sulfides using S-methylisothiourea sulfate under transition-metal-free conditions

In the presence of cesium carbonate, an efficient synthesis of aryl methyl sulfides by the reactions of aryl halides with commercially available S-methylisothiourea sulfate is developed. This odourless and highly crystalline solid can be used as the substitute for malodorous methanethiol. The gram-scale reaction also proceeds smoothly without the use of column chromatography separation. Similarly, 2-(dimethylamino)ethylthio and cyclopropylmethylthio groups can be easily introduced into the aromatic rings from the corresponding S-[2-(dimethylamino)ethyl]isothiourea dihydrochloride and S-cyclopropylmethylisothiourea hydrobromide. The possible reaction mechanism is proposed. It is believed that this route to aryl alkyl sulfides is well competitive with currently known methods due to its wide substrate scope, excellent yields, easy operation and transition-metal-free conditions.

Radical difluoromethylthiolation of aromatics enabled by visible light

Direct introduction of a difluoromethylthio group (-SCF2H) to arenes represents an efficient route to access a valuable catalogue of organofluorines; however, to realize this transformation under metal-free and mild conditions still remains challenging and rarely reported. Herein, a metal-catalyst-free and redox-neutral innate difluoromethylthiolation method with a shelf-stable and readily available reagent, PhSO2SCF2H, under visible light irradiation is described. This light-mediated protocol successfully converts a broad spectrum of arenes and heteroarenes to difluoromethylthioethers in the absence of noble metals and stoichiometric amounts of additives.

Visible light-promoted difluoromethylthiolation of aryldiazonium salts

Difluoromethylthiolation of aryldiazonium salts under mild conditions using a shelf-stable reagent (PhSO₂SCF₂H) was reported.

Pd-Catalyzed C(sp2)–H aminocarbonylation using the Langlois reagent as a carbonyl source

An efficient Pd-catalyzed C(sp²)–H aminocarbonylation of aryl carboxamides assisted by an N,S-bidentate directing group was developed.