A Recyclable Inorganic Lanthanide Cluster Catalyst for Chemoselective Aerobic Oxidation of Thiols

Optimizing lanthanide catalyst performance with organic ligands often encounters significant challenges, including susceptibility to water or oxygen and complex synthesis pathways. To address these issues, our research focuses on developing inorganic lanthanide clusters with enhanced stability and functionality. In this study, we introduce the [Sm6O(OH)8(H2O)24]I8(H2O)8 cluster (Sm-OC) as a sustainable and efficient catalyst for the aerobic oxidation of thiols under heating conditions. The Sm-OC catalyst demonstrated remarkable stability, outstanding recyclability, and excellent chemoselectivity across a diverse range of functional groups in 38 different tests. Notably, it enables efficient unsymmetrical disulfide synthesis and prevents the formation of over-oxidized by-products, highlighting its superior performance. This Sm-OC catalyst provides a practical and robust tool for the precise construction of versatile disulfides, thus establishing a template for the broader use of lanthanide clusters in organic synthesis.

1,6-Nucleophilic Di- and Trifluoromethylation of para-Quinone Methides with Me3SiCF2H/Me3SiCF3 Facilitated by CsF/18-Crown-6

The direct 1,6-nucleophilic difluoromethylation, trifluoromethylation, and difluoroalkylation of para-quinone methides (p-QMs) with Me3SiRf (Rf = CF2H, CF3, CF2CF3, CF2COOEt, and CF2SPh) under mild conditions are described. Although Me3SiCF2H shows lower reactivity than Me3SiCF3, it can react with p-QMs promoted by CsF/18-Crown-6 to give structurally diverse difluoromethyl products in good yields. The products can then be further converted into fluoroalkylated para-quinone methides and α-fluoroalkylated diarylmethanes.

Application of Iodine as a Catalyst in Aerobic Oxidations: A Sustainable Approach for Thiol Oxidations

Iodine is a well-known oxidant that is widely used in organic syntheses. Thiol oxidation by stoichiometric iodine is one of the most commonly employed strategies for the synthesis of valuable disulfides. While recent advancements in catalytic aerobic oxidation conditions have eliminated the need for stoichiometric oxidants, concerns persist regarding the use of toxic or expensive catalysts. In this study, we discovered that iodine can be used as a cheap, low-toxicity catalyst in the aerobic oxidation of thiols. In the catalytic cycle, iodine can be regenerated via HI oxidation by O2 at 70 °C in EtOAc. This protocol harnesses sustainable oxygen as the terminal oxidant, enabling the conversion of primary and secondary thiols with remarkable efficiency. Notably, all 26 tested thiols, encompassing various sensitive functional groups, were successfully converted into their corresponding disulfides with yields ranging from >66% to 98% at a catalyst loading of 5 mol%.

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.

Diaryl disulfides and thiosulfonates as combretastatin A-4 analogues: Synthesis, cytotoxicity and antitubulin activity

Diaryl disulfides and diaryl thiosulfonates were synthesized with the two phenyl rings of all compounds bearing identical halide substituents. Because of structural similarity to the potent antimitotic natural product combretastatin A-4 (CA-4), the compounds were examined for inhibition of tubulin polymerization, and the thiosulfonates were more active than the disulfides. The nine thiosulfonates had IC50 values ranging from 1.2 to 9.1 µM, as compared with 1.3 µM obtained with CA-4. The compounds thus ranged from equipotent with CA-4 to 7-fold less active. The nine disulfides had IC50 values ranging from 1.2 to 5.1 µM, as compared with 0.54 µM obtained with CA-4. The compounds thus ranged from less than half as active as CA-4 to over 9-fold less active. The most active members of each group, 2 g and 3c, in the assembly assay were modeled into the colchicine site. Compound 3c had significant hydrophobic interactions with β-tubulin residues CYS 241 and ALA 250, and its thiosulfonate bridge made a hydrogen bond with β-tubulin residue ASN 258. Compound 2 g had hydrophobic interactions with β-tubulin residues ALA 250, CYS 241 and ALA 254, but there was no significant interaction of the disulfide bridge with tubulin.

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.

Insertion of Carbenes into Deprotonated nido-Undecaborane, B11H13(2-)

We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2- dianion to form the [closo-1-CB11H12]- anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient and scalable and proceeds with 70-90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14]- to [closo-1-CB11H12]-, and CCl2 and CBr2, which require more.

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.

One-pot multistep mechanochemical synthesis of fluorinated pyrazolones

Solventless mechanochemical synthesis represents a technique with improved sustainability metrics compared to solvent-based processes. Herein, we describe a methodical process to run one solventless reaction directly into another through multistep mechanochemistry, effectively amplifying the solvent savings. The approach has to consider the solid form of the materials and compatibility of any auxiliary used. This has culminated in the development of a two-step, one-jar protocol for heterocycle formation and subsequent fluorination that has been successfully applied across a range of substrates, resulting in 12 difluorinated pyrazolones in moderate to excellent yields.

Direct Monofluoromethylthiolation with S-(Fluoromethyl) Benzenesulfonothioate

An electrophilic shelf-stable monofluoromethylthiolating reagent S-(fluoromethyl) benezenesulfonothioate (1) was developed. In the presence of a copper catalyst, reagent 1 coupled with a variety of aryl boronic acids to give the corresponding monofluoromethylthiolated arenes in high yields. In addition, addition of reagent 1 to alkyl alkenes in the presence of a silver catalyst gave alkyl monofluoromethylthioethers in high yields.

PhSO2 SCF2 H: A Shelf-Stable, Easily Scalable Reagent for Radical Difluoromethylthiolation

A new shelf-stable and easily scalable difluoromethylthiolating reagent S-(difluoromethyl) benzenesulfonothioate (PhSO₂ SCF₂ H) was developed. PhSO₂ SCF₂ H is a powerful reagent for radical difluoromethylthiolation of aryl and alkyl boronic acids, decarboxylative difluoromethylthiolation of aliphatic acids, and a phenylsulfonyl-difluoromethylthio difunctionalization of alkenes under mild reaction conditions.

Recent Advances in the Synthesis of SCF2 H- and SCF2 FG-Containing Molecules

In recent years, much interest has been paid to difluoromethylthiolated molecules as the "SCF₂ " moiety is a key motif in drug and agrochemical research. Consequently, the development of versatile strategies for the selective synthesis of SCF₂ H- and SCF₂ FG-containing molecules (FG=functional group) has attracted a lot of attention and inspired the scientific community to design new tools. This Minireview highlights the major progress made in this field. Particularly, methodologies developed for the difluoromethylation of sulfur-containing molecules and the direct construction of C-SCF₂ bonds in various classes of compounds are showcased and discussed.