Sulfonate Research Articles

Reactivity of Electrophilic Trifluoromethylating Reagents

AbstractKinetics of the reactions of colored carbanions (reference nucleophiles) with S‐(trifluoromethyl)dibenzothiophenium ions (Umemoto's reagents) and hypervalent trifluoromethyl‐substituted iodine compounds (Togni's reagents) have been determined photometrically using stopped‐flow techniques. The second‐order rate constants k2(20 °C) for the reactions of Umemoto's sulfonium ions (generation I and II) with the reference nucleophiles in DMSO follow the correlation lg k2(20 °C)=sN(N+E) and can be used to determine the electrophilicity parameters E of these trifluoromethylating reagents. It is shown that the conditions reported for the reactions of Umemoto's generation I reagents with a variety of C‐nucleophiles are in line with the electrophilicity parameter E≈−13 determined for these reagents. Though Togni's hypervalent iodine‐based trifluoromethylation reagents do not follow this linear free energy relationship, the kinetics of their reactions with carbanions indicate that they cover the same reactivity range as Umemoto's generation I and II reagents.

Ligand-promoted reductive coupling between aryl iodides and cyclic sulfonium salts by nickel catalysis

Ligand-promoted reductive coupling between aryl iodides and cyclic sulfonium salts by nickel catalysis

Effect of Lignin Structure Characteristics on the Performance of Lignin Based Phenol Formaldehyde Adhesives.

As the second most abundant biopolymer, lignin remains underutilized in various industrial applications. Various forms of lignin generated from different methods affect its physical and chemical properties to a certain extent. To promote the broader commercial utilization of currently available industrial lignins, lignin sulfonate (SL), kraft lignin (KL), and organosolv lignin (OL) are utilized to partially replace phenol in the synthesis of phenol formaldehyde (PF) adhesives. The impact of lignin production process on the effectiveness of lignin-based phenolic (LPF) adhesives is examined based on the structural analysis of the selected industrial lignin. The results show that OL has more phenolic hydroxyl groups, lower molecular weight, and greater number of reactive sites than the other two types of lignins. The maximum replacement rate of phenol by OL reaches 70% w/w, resulting in organosolv lignin phenolic (OLPF) adhesives with a viscosity of 960 mPa·s, a minimal free formaldehyde content of 0.157%, and a shear strength of 1.84MPa. It exhibits better performance compared with the other two types of lignin-based adhesives and meets the requirements of national standards.

Pseudocyclic Arylbenziodoxaboroles as Water-Triggered Aryne Precursors in Reactions with Organic Sulfides.

Pseudocyclic arylbenziodoxaboroles are unique aryne precursors under neutral aqueous conditions that selectively react with organic sulfides, forming the corresponding sulfonium salts. This reaction is compatible with various substituents (alkyl, halogen, CN, NO2, CHO, and cyclopropyl) in the aromatic ring or alkyl group of the sulfide. Similar reactions of sulfoxides afford o-hydroxy-substituted sulfonium salts. The structures of key products were confirmed by X-ray analysis.

Synthesis and antibacterial properties of alkyl substituted sulfonium salt

The development of new antibacterial agents is particularly important in the battle against pathogenic microorganisms. In this study, sulfonium ions were used as the structural core to synthesize alkyl-substituted ionic compounds as antibacterial agents. The antimicrobial activity of sulfonium ionic compounds against Escherichia coli and Staphylococcus aureus was analyzed by measurement of the minimum inhibitory concentration and minimum bactericidal concentration. The effects of sulfonium salts on cell membrane integrity and permeability were investigated by detecting the extracellular proteins leakage of E. coli and S. aureus upon contact treatment, and observing the bacteria’s ultrastructural changes with transmission electron microscopy. The results showed that all the sulfonium salts exhibited resistant activity. Sulfonium salt with alkyl chain length of 16 carbon presented the strongest resistance with MIC of 30 and 3.75 μmol/L, and MBC of 120 and 60 μmol/L against E. coli and S. aureus, respectively. After treatment with sulfonium salts, the permeability of the membrane of E. coli and S. aureus cells changed, and the exudation of extracellular proteins increased significantly. The transmission electron microscope showed that the surface of the bacteria had shrunk and the cell walls had burst. The group of sulfonium salt compounds can destroy the integrity of cell membrane and change membrane permeability to achieve antibacterial purposes.

Trifluoromethyl Rhodium‐Carbynoid in [2+1+2] Cycloadditions

AbstractTrifluoromethyl cationic carbyne (CF3C+:) possessing dual carbene‐carbocation behavior emulated as trifluoromethyl metal‐carbynoid (CF3C+=M) has not been explored yet, and its reaction characteristics are unknown. Herein, a novel α‐diazotrifluoroethyl sulfonium salt was prepared and used in Rh‐catalyzed three‐component [2+1+2] cycloadditions for the first time with commercially available N‐fused heteroarenes and nitriles, yielding a series of imidazo[1,5‐a] N‐heterocycles that are of interest in medicinal chemistry, in which the insertion of trifluoromethyl Rh‐carbynoid (CF3C+=Rh) into C=N bonds of N‐fused heteroarenes was involved. This strategy demonstrates synthetic applications in late‐stage modification of pharmaceuticals, construction of CD3‐containing N‐heterocycles, gram‐scale experiments, and synthesis of phosphodiesterase 10A inhibitor analog. These highly valuable and modifiable imidazo[1,5‐a] N‐heterocycles exhibit good antitumor activity in vitro, thus demonstrating their potential applications in medicinal chemistry.

Trifluoromethyl Rhodium-Carbynoid in [2+1+2] Cycloadditions.

Trifluoromethyl cationic carbyne (CF3 C+ :) possessing dual carbene-carbocation behavior emulated as trifluoromethyl metal-carbynoid (CF3 C+ =M) has not been explored yet, and its reaction characteristics are unknown. Herein, a novel α-diazotrifluoroethyl sulfonium salt was prepared and used in Rh-catalyzed three-component [2+1+2] cycloadditions for the first time with commercially available N-fused heteroarenes and nitriles, yielding a series of imidazo[1,5-a] N-heterocycles that are of interest in medicinal chemistry, in which the insertion of trifluoromethyl Rh-carbynoid (CF3 C+ =Rh) into C=N bonds of N-fused heteroarenes was involved. This strategy demonstrates synthetic applications in late-stage modification of pharmaceuticals, construction of CD3 -containing N-heterocycles, gram-scale experiments, and synthesis of phosphodiesterase 10A inhibitor analog. These highly valuable and modifiable imidazo[1,5-a] N-heterocycles exhibit good antitumor activity in vitro, thus demonstrating their potential applications in medicinal chemistry.

Hydroxylation of Aryl Sulfonium Salts for Phenol Synthesis under Mild Reaction Conditions.

Hydroxylation of aryl sulfonium salts could be realized by utilizing acetohydroxamic acid and oxime as hydroxylative agents in the presence of cesium carbonate as a base, leading to a variety of structurally diverse hydroxylated arenes in 47-95% yields. In addition, the reaction exhibited broad functionality tolerance, and a range of important functional groups (e.g., cyano, nitro, sulfonyl, formyl, keto, and ester) could be well amenable to the mild reaction conditions.

Base-Promoted Ring-Opening Hydroxylation of Cyclic Sulfonium Salts.

Herein, we reported a general strategy for the synthesis of sulfur-containing primary alcohol derivatives by base-promoted ring-opening hydroxylation of cyclic sulfonium salts. A variety of sulfonium salts were successfully transformed into the desired hydroxylated products in moderate to excellent yields with good functional group tolerance. Moreover, the one-pot synthesis, scale-up reaction, and late-stage functionalization of complex molecules demonstrated the practicability of this synthetic protocol in the field of synthetic chemistry.

Synthesis of Benzofuran-Fused Oxepines through Cs2CO3-Promoted [4 + 3] Annulation of Aurones with Crotonate-Derived Sulfonium Salts.

Benzofuran-fused derivatives display important and reliable therapeutic properties. Herein, we describe the synthesis of benzofuran-fused oxepines using aurones and crotonate-derived sulfonium salts via a [4 + 3] annulation reaction in the presence of Cs2CO3. This reaction proceeds under mild and operationally simple conditions. The synthetic utility of this approach was highlighted by several transformations, including the efficient synthesis of a novel tetracyclic fused benzofuran derivative.

Synthesis, Characterization, and Evaluation of Sulfonium Lipids as Potential Nonviral Gene Vectors

Introduction: Non-viral gene vectors have attracted much attention in the last few decades because of their potential activity and fewer side effects. Headgroup chemistry is a key aspect of lipid design. Methods: In this study, a group of sulfonium lipids were designed and constructed by combining tetrahydrothiophene or tetrahydrothiopyran with an ethoxy linker and carbon aliphatic chains and were evaluated in terms of their ability as potential gene vectors. The sulfonium lipids were synthesized and characterized by 1H NMR, 13C NMR, and Mass. Condensates of sulfonium lipids (SL) and DNA were examined by gel electrophoresis and particle size and zeta potential were measured. Sulfonium compounds were tested on HepG2 cells for cytotoxicity. SL/DNA condensates were studied in cellular uptake and distribution using fluorescent microscopy. Results: 12 sulfonium lipids were obtained. Gel electrophoresis experiments showed that sulfonium cation can effectively interact with phosphorous in DNA. Compounds containing longer lipid chains can effectively retard DNA at an S/P ratio higher than 10/1 and can condense DNA into nano size particles with particle size in the range of 150 nm ~ 300 nm and zeta potential in the range of +20~+40. Sulfonium compounds were calculated against HepG2 cells in the range of 0.035 μg/mL to 1.64 μg/mL. The intracellular uptake experiments revealed that SL/DNA nanoparticle was taken into the cell at low efficiency. Conclusion: Sulfonium head group can interact with the phosphates of DNA. The structural environment of sulfonium ions influences the DNA bonding effect. The designed cyclic sulfonium ion was buried in the middle of the structure and thus hindered interaction with DNA. This type of molecule is worthy of further modification to increase DNA capacity and reduce cell cytotoxicity.

DMSO-DCE Triggered Chemodivergent C-Methylenation of Electron-Rich Arenes: An Easy Access to Diarylmethanes.

The chemodivergent property of dimethyl sulfoxide (DMSO) along with 1,2-dichloroethane (DCE) was exploited for the incorporation of a methylene group to form diarylmethanes through a dearomatization/rearomatization process. Methyl(methylene)sulfonium ions (CH2=S+-Me) were generated by simple heating of commonly used solvents such as DMSO and DCE. These ions were subsequently trapped by electron-rich arenes and heteroarenes, resulting in the synthesis of both symmetrical and unsymmetrical diarylmethanes. This protocol was further extended to access N-methylenamides by reacting 2-naphthol with amides or nitriles in the presence of DMSO and DCE.

Direct Site‐Selective Difunctionalization of Pyrazoles

AbstractThis study presents a protocol for the direct site‐selective difunctionalization of pyrazoles under mild reaction conditions. This protocol showcase a notable site‐selectivity and encompasses a wide substrate scope. Detailed mechanistic investigations elucidate the dual role of the sulfonium salt acting both as the reaction substrate and acid donor, thereby effectively catalyzing the reaction. The demonstrated one‐pot synthesis, scale‐up reaction and subsequent product modifications can assist in advancing the potential application of this protocol in organic synthesis and its associated domains.

Molecular structure effects of passivation agents on the performance of perovskite solar cells

The performance of perovskite solar cells (PSCs) is affected by a non-radiative recombination process involving defects in the perovskite films. To tackle this challenge, herein, aryl sulfonates and alkyl sulfates with distinct molecular structures, specifically sodium benzenesulfonate (SBS) and sodium dodecyl sulfate (SDS), as additives to passivate the defects in the methyl ammonium lead iodide (MAPbI3) perovskite films. This study examines the impact of the molecular structure of these additives on both the characteristics of the perovskite films and the performance of the PSCs. The results demonstrate that both SBS and SDS, which contain –S-O- and Na+ ions in their structures, effectively increase the efficiency of PSCs. This improvement is attributed to the ability of these ions to interact with oppositely charged defects, leading to reduced trap densities in the perovskite films. Remarkably, SDS stands out with its long alkyl chain and a larger head group (C-O-S-O-) carrying a higher negative charge, showcasing superior defect passivation compared to SBS. The SBS molecule, on the other hand, features a phenyl group and a smaller head group (C-S-O-) with a reduced negative charge. This is primarily due to the significant role played by the phenyl ring in delocalizing the negative charge. As a result, the SDS-treated PSCs can achieve a remarkable champion power conversion efficiency of 20.70 %. Additionally, the contact angle of water on the SDS-treated perovskite films surpasses that on the SBS-treated film. This highlights an enhanced hydrophobic characteristic, ultimately bolstering the stability of SDS-treated PSCs.

Catalytic Enantioselective Nucleophilic α-Chlorination of Ketones with NaCl.

Catalytic enantioselective α-chlorination of ketones is a highly desirable process. Different from the conventional approaches that employ corrosive electrophilic chlorination reagents, the process disclosed here employs nucleophilic chloride, aqueous NaCl solution, and even seawater, as green inexpensive chlorine sources. This mechanistically distinct and electronically opposite approach provides facile access to diverse highly enantioenriched acyclic α-chloro ketones that are less straightforward by conventional approaches. With a chiral thiourea catalyst, a range of racemic α-keto sulfonium salts underwent enantioconvergent carbon-chlorine bond formation with high efficiency and excellent enantioselectivity under mild conditions. The sulfonium motif plays a crucial triple role by permitting smooth dynamic kinetic resolution to take place via a chiral anion binding mechanism in a well-designed phase-transfer system. This protocol represents a new general platform for the asymmetric nucleophilic α-functionalization of carbonyl compounds.

Shining light on sulfonium salts and sulfur ylides: recent advances in alkylation under photoredox catalysis

Recent advancements in photoredox alkylation with sulfur ylides, sulfonium salts and related analogues are summarized in this review.

Site-selective S-gem-difluoroallylation of unprotected peptides with 3,3-difluoroallyl sulfonium salts.

Bench-stable 3,3-difluoroallyl sulfonium salts (DFASs), featuring tunable activity and their editable C-β and gem-difluoroallyl group, proved to be versatile fluoroalkylating reagents for site-selective S-gem-difluoroallylation of cysteine residues in unprotected peptides. The reaction proceeds with high efficiency under mild conditions (ambient temperature and aqueous and weak basic conditions). Various protected/unprotected peptides, especially bioactive peptides, are site-selectively S-gem-difluoroallylated. The newly added gem-difluoroallyl group and other functional groups derived from C-β of DFASs are poised for ligation with bio-functional groups through click and radical chemistry. This stepwise "doubly orthogonal" modification of peptides enables the construction of bioconjugates with enhanced complexity and functionality. This proof of principle is successfully applied to construct a peptide-saccharide-biotin chimeric bioconjugate, indicating its great potential application in medicinal chemistry and chemical biology.

Four-component radical-polar crossover cyclization involving double insertion of SO2 to β-sulfonyl sultines

An unprecedented four-component radical-polar crossover cyclization (RPCC) protocol involving double insertion of SO2 was developed. Various sulfonium salts and alkyl boronic acids were transformed into functionalized β-sulfonyl sultines with S(iv) and S(vi) centers.

Late-stage gem-difluoroallylation of phenol in bioactive molecules and peptides with 3,3-difluoroallyl sulfonium salts.

An efficient method for the late-stage selective O-fluoroalkylation of tyrosine residues with a stable yet highly reactive fluoroalkylating reagent, 3,3-difluoroallyl sulfonium salts (DFASs), has been developed. The reaction proceeds in a mild basic aqueous buffer (pH = 11.6) with high efficiency, high biocompatibility, and excellent regio- and chemoselectivity. Various oligopeptides and phenol-containing bioactive molecules, including carbohydrates and nucleosides, could be selectively O-fluoroalkylated. The added vinyl and other functional groups from DFASs can be valuable linkers for successive modification, significantly expanding the chemical space for further bioconjugation. The synthetic utility of this protocol has been demonstrated by the fluorescently labeled anti-cancer drug and the synthesis of O-link type 1,4,7,10-tetraazacyclododecane-N,N',N,N'-tetraacetic acid-tyrosine3-octreotate (DOTA-TATE), showing the prospect of the method in medicinal chemistry and chemical biology.

Reactivity of α-diazo sulfonium salts: rhodium-catalysed ring expansion of indenes to naphthalenes.

In the presence of catalytic amounts of the paddlewheel dirhodium complex Rh2(esp)2, α-diazo dibenzothiophenium salts generate highly electrophilic Rh-coordinated carbenes, which evolve differently depending on their substitution pattern. Keto-moieties directly attached to the azomethinic carbon promote carbene insertion into one of the adjacent C-S bonds, giving rise to highly electrophilic dibenzothiopyrilium salts. This intramolecular pathway is not operative when the carbene carbon bears ester or trifluoromethyl substituents; in fact, these species react with olefins delivering easy to handle cyclopropyl-substituted sulfonium salts. When indenes are the olefins of choice, the initially formed cyclopropyl rings smoothly open with concomitant departure of dibenzothiophene, enabling access to a series of 2-functionalized naphthalenes.