Transition-metal-free formal cross-coupling of aryl methyl sulfoxides and alcohols via nucleophilic activation of C-S bond

Electrochemical desulfurative formation of C-N bonds through selective activation of inert C(sp3)-S bonds

In this study, we introduce an efficient, metal-free electrocatalytic desulfurative protocol for forming C-N bonds by selectively activating inert C(sp3)-S bonds of alkyl thioethers. This method offers a straightforward and environmentally friendly approach for modification of heterocyclic compounds from readily accessible thioethers. Preliminary mechanistic investigations suggest that the reaction proceeds via a carbocation intermediate. Furthermore, successful synthesis on a 10-gram scale was achieved in a continuous flow electrochemical reactor.

Decarboxylative Sulfinylation Enables a Direct, Metal-Free Access to Sulfoxides from Carboxylic Acids

The intermediate oxidation state of sulfoxides is central to the plethora of their applications in chemistry and medicine, yet it presents challenges for an efficient synthetic access, limiting the structural diversity of currently available sulfoxides. Here, we report a data-guided development of direct decarboxylative sulfinylation that enables the previously inaccessible functional group interconversion of carboxylic acids to sulfoxides in a reaction with sulfinates. Given the broad availability of carboxylic acids and the growing synthetic potential of sulfinates, the direct decarboxylative sulfinylation is poised to improve the structural diversity of synthetically accessible sulfoxides. The reaction is facilitated by a kinetically favored sulfoxide formation from the intermediate sulfinyl sulfones, despite the strong thermodynamic preference for the sulfone formation, unveiling the previously unknown and chemoselective radicalophilic sulfinyl sulfone reactivity.

KuQuinone as a Highly Stable and Reusable Organic Photocatalyst in Selective Oxidation of Thioethers to Sulfoxides

A chemoselective photocatalytic system to perform thioether oxidation to sulfoxide is presented. The light-induced oxidation process is here promoted by a metal-free quinoid catalyst, namely 1-hexylKuQuinone (KuQ). Reactions performed in a fluorinated solvent (i.e., HFIP), using O₂ as the oxidant, at room temperature, lead to complete thioanisole conversion to methyl phenyl sulfoxide in 60 min. Remarkably, the system can be recharged and recycled without a loss of activity and selectivity, reaching turnover numbers (TONs) higher than 4000. Excellent catalytic performances and full selectivity have also been obtained for the photocatalytic oxidation of substituted thioanisole derivatives, aliphatic, cyclic, and diaryl thioethers. Likewise, the oxidation of heteroaromatic organosulfur compounds can be accomplished, with longer reaction times.

Nickel-Catalyzed Direct Cross-Coupling of Diaryl Sulfoxide with Aryl Bromide

The direct cross-couplings of diaryl sulfoxides with aryl bromides via C-S bond cleavage could be readily accomplished using nickel(II) as the catalyst, 1,2-bis(diphenylphosphino)ethane (dppe) as the ligand, and magnesium turnings as the reducing metal in THF, leading to the corresponding biaryls in moderate to good yields. The reaction exhibited a broad substrate scope and could be applied to a gram-scale synthesis. The "one-pot" reaction, which avoids the utility of presynthesized and moisture-labile organometallic compounds, is operationally simple and step-economic.

Transition-Metal-Free O-Arylation of Alcohols and Phenols with S-Arylphenothiaziniums

Herein, we report the transition-metal-free O-arylation of alcohols and phenols with S-arylphenothiaziniums, which can be easily synthesized from boronic acids. Aryl substituents derived from arylboronic acids were selectively introduced into the hydroxy groups in alcohols and phenols, and a variety of aryl ethers were synthesized. This selectivity is supported by theoretical calculations.

Synthesis of Polysubstituted Ferrocenesulfoxides

The purpose of the study is to design synthetic methodologies, especially directed deprotometalation using polar organometallic reagents, to access polysubstituted ferrocenesulfoxides. From enantiopure 2-substituted (SiMe₃, PPh₂) S-tert-butylferrocenesulfoxides, a third substituent was first introduced at the 5 position (SiMe₃, I, D, C(OH)Ph₂, Me, PPh₂, CH₂NMe₂, F) and removal of the trimethylsilyl group then afforded 2-substituted ferrocenesulfoxides unreachable otherwise. Attempts to apply the “halogen dance” reaction to the ferrocenesulfoxide series led to unexpected results although rationalized in light of calculated pK_a values. Further functionalizations were also possible. Thus, new enantiopure, planar chiral di- and trisubstituted ferrocenes have been obtained, in addition to several original 2-substituted, 2,3- and 2,5-disubstituted, 2,3,5-trisubstituted and even 2,3,4,5-tetrasubstituted ferrocenesulfoxides, also enantiopure.

Electrochemical dual-oxidation strategy enables access to α-chlorosulfoxides from sulfides

Electrochemistry contributes a strong tool for the manufacture of molecules, addressing intractable challenges in synthetic chemistry by enabling innovative reaction pathways. Herein, a bifunctional reagent, aqueous hydrochloric acid, is used to establish an electrochemical selective dual-oxidation approach that gives access to α-chlorosulfoxides from sulfides. This strategy presents broad substrate scope, high diastereoselectivity, and regioselectivity. The late-stage modification of amino acids and pharmaceutical derivatives further highlights the utility. Furthermore, detailed mechanistic studies reveal that the key success for this selective chemical transformation is the dual-oxidation process at the anode. This electrochemical dual-oxidation strategy may have wide universality; we anticipate diverse applications of this protocol across the many fields of chemistry.

Radical Anion Promoted Chemoselective Cleavage of Csp2-S Bond Enables Formal Cross-Coupling of Aryl Methyl Sulfones with Alcohols

A novel formal cross-coupling of aryl methyl sulfones and alcohols affording alkyl aryl ethers via an S_RN1 pathway is developed. Two marketed antitubercular drugs were efficiently prepared employing this approach as the key step. A dimsyl-anion initiated radical chain process was revealed as the major pathway. DFT calculations indicate that the formation of a radical anion via nucleophilic addition of alkoxide to the aryl radical is the key step in determining the observed chemoselectivity.

A nickel-catalyzed silylation reaction of alkyl aryl sulfoxides with silylzinc reagents

Ni(PEt3)Cl2-catalyzed silylation of alkyl aryl sulfoxides with silylzinc reagents was carried out. This protocol allows alkyl aryl sulfoxides to convert to arylsilicon compounds under mild reaction conditions, tolerates a range of functional groups and is suitable for a wide scope of substrates.

Ni-Catalyzed Borylation of Aryl Sulfoxides

A nickel/N-heterocyclic carbene (NHC) catalytic system has been developed for the borylation of aryl sulfoxides with B2 (neop)2 (neop=neopentyl glycolato). A wide range of aryl sulfoxides with different electronic and steric properties were converted into the corresponding arylboronic esters in good yields. The regioselective borylation of unsymmetric diaryl sulfoxides was also feasible leading to borylation of the sterically less encumbered aryl substituent. Competition experiments demonstrated that an electron-deficient aryl moiety reacts preferentially. The origin of the selectivity in the Ni-catalyzed borylation of electronically biased unsymmetrical diaryl sulfoxide lies in the oxidative addition step of the catalytic cycle, as oxidative addition of methoxyphenyl 4-(trifluoromethyl)phenyl sulfoxide to the Ni(0) complex occurs selectively to give the structurally characterized complex trans-[Ni(ICy)2 (4-CF3 -C6 H4 ){(SO)-4-MeO-C6 H4 }] 4. For complex 5, the isomer trans-[Ni(ICy)2 (C6 H5 )(OSC6 H5 )] 5-I was structurally characterized in which the phenyl sulfinyl ligand is bound via the oxygen atom to nickel. In solution, the complex trans-[Ni(ICy)2 (C6 H5 )(OSC6 H5 )] 5-I is in equilibrium with the S-bonded isomer trans-[Ni(ICy)2 (C6 H5 )(SOC6 H5 )] 5, as shown by NMR spectroscopy. DFT calculations reveal that these isomers are separated by a mere 0.3 kJ/mol (M06/def2-TZVP-level of theory) and connected via a transition state trans-[Ni(ICy)2 (C6 H5 )(η2 -{SO}-C6 H5 )], which lies only 10.8 kcal/mol above 5.

Iterative Exponential Growth of Oxygen-Linked Aromatic Polymers Driven by Nucleophilic Aromatic Substitution Reactions

This work presents the first transition metal-free synthesis of oxygen-linked aromatic polymers by integrating iterative exponential polymer growth (IEG) with nucleophilic aromatic substitution (SNAr) reactions. Our approach applies methyl sulfones as the leaving groups, which eliminate the need for a transition metal catalyst, while also providing flexibility in functionality and configuration of the building blocks used. As indicated by 1) 1H-1H NOESY NMR spectroscopy, 2) single-crystal X-ray crystallography, and 3) density functional theory (DFT) calculations, the unimolecular polymers obtained are folded by nonclassical hydrogen bonds formed between the oxygens of the electron-rich aromatic rings and the positively polarized C-H bonds of the electron-poor pyrimidine functions. Our results not only introduce a transition metal-free synthetic methodology to access precision polymers but also demonstrate how interactions between relatively small, neutral aromatic units in the polymers can be utilized as new supramolecular interaction pairs to control the folding of precision macromolecules.

Photocatalytic Reductive C-O Bond Cleavage of Alkyl Aryl Ethers by Using Carbazole Catalysts with Cesium Carbonate

Methods to activate the relatively stable ether C-O bonds and convert them to other functional groups are desirable. One-electron reduction of ethers is a potentially promising route to cleave the C-O bond. However, owing to the highly negative redox potential of alkyl aryl ethers (E^red < -2.6 V vs SCE), this mode of ether C-O bond activation is challenging. Herein, we report the visible-light-induced photocatalytic cleavage of the alkyl aryl ether C-O bond using a carbazole-based organic photocatalyst (PC). Both benzylic and non-benzylic aryl ethers underwent C-O bond cleavage to form the corresponding phenol products. Addition of Cs₂CO₃ was beneficial, especially in reactions using a N-H carbazole PC. The reaction was proposed to occur via single-electron transfer (SET) from the excited-state carbazole to the substrate ether. Interaction of the N-H carbazole PC with Cs₂CO₃ via hydrogen bonding exists, which enables a deprotonation-assisted electron-transfer mechanism to operate. In addition, the Lewis acidic Cs cation interacts with the substrate alkyl aryl ether to activate it as an electron acceptor. The high reducing ability of the carbazole combined with the beneficial effects of Cs₂CO₃ made this otherwise formidable SET event possible.

The recent advancement of low-dimensional nanostructured materials for drug delivery and drug sensing application: A brief review

In this review article, we have presented a detailed analysis of the recent advancement of quantum mechanical calculations in the applications of the low-dimensional nanomaterials (LDNs) into biomedical fields like biosensors and drug delivery systems development. Biosensors play an essential role for many communities, e.g. law enforcing agencies to sense illicit drugs, medical communities to remove overdosed medications from the human and animal body etc. Besides, drug delivery systems are theoretically being proposed for many years and experimentally found to deliver the drug to the targeted sites by reducing the harmful side effects significantly. In current COVID-19 pandemic, biosensors can play significant roles, e.g. to remove experimental drugs during the human trials if they show any unwanted adverse effect etc. where the drug delivery systems can be potentially applied to reduce the side effects. But before proceeding to these noble and expensive translational research works, advanced theoretical calculations can provide the possible outcomes with considerable accuracy. Hence in this review article, we have analyzed how theoretical calculations can be used to investigate LDNs as potential biosensor devices or drug delivery systems. We have also made a very brief discussion on the properties of biosensors or drug delivery systems which should be investigated for the biomedical applications and how to calculate them theoretically. Finally, we have made a detailed analysis of a large number of recently published research works where theoretical calculations were used to propose different LDNs for bio-sensing and drug delivery applications.

Aryl Ether Syntheses via Aromatic Substitution Proceeding under Mild Conditions

In this study, mild conditions for aromatic substitutions during the syntheses of aryl ethers were developed. In the reaction conditions, the choices of solvent, base, and the sequence for the addition of the reagents proved important. A wide variety of alcohols were used directly as nucleophiles and smoothly reacted with aryl chlorides that possessed either a nitro or a cyano group at either the ortho- or para-position. Controlled experiments we performed suggested that the reaction underwent a charge-transfer process mediated by a combination of DMF and tert-BuOK.