Thiyl radicals in organic synthesis

Hydrodealkenylative C(sp3)-C(sp2) Bond Fragmentation Using Isayama-Mukaiyama Peroxidation

Advancements in radical capture strategies have expanded the range of products accessible from alkenes through dealkenylative synthesis. These methods, however, are still limited, as they rely on ozonolysis to generate the key peroxide intermediates from alkenes. Ozonolysis has several limitations. It is not compatible with alkenes containing electron-rich aromatics. It is also inapplicable to certain alkene substitution patterns in the context of dealkenylative synthesis. Additionally, it struggles with sterically hindered alkenes, internal nucleophiles and electrophiles, and allylic alcohols. In this paper, using Isayama-Mukaiyama peroxidation (IMP), we address the limitations of ozonolysis to rescue previously inaccessible alkene substrates and broaden the applicability of dealkenylative functionalization. In particular, we apply IMP in hydrodealkenylation and describe a novel radical hydrogenation condition─employing catalytic [FeIII], catalytic benzenethiol, and γ-terpinene in refluxing methanol─to resolve β-scission issues associated with IMP-generated alkyl silylperoxides.

Visible-light-induced thiol-ene/air oxidation tandem reaction for sulfoxide synthesis: a photocatalyst-free and metal-free approach

A photocatalyst-free, metal-free visible light-promoted thiol-ene/oxidation tandem reaction for sulfoxide synthesis has been developed under mild conditions with air as oxidant. Broad substrate scope as well as gram-scale synthesis enables this environmentally friendly approach with potential for further synthetic applications.

Harnessing radical mediated reactions of thioacids for organic synthesis

Thiyl radical mediated reactions are of burgeoning importance for organic synthesis. This Feature Article focuses specifically on thioacid- and thioacetate-derived thiyl radicals as versatile intermediates for the synthesis of a diverse range of organic compounds under mild conditions with a high degree of chemo-, regio- and diastereoselectivity. We review recent developments in the field, including novel approaches for radical initiation, strategies for the synthesis of a wide range of functional groups, peptide and glycan diversification, protein labelling and radical dethiocarboxylation. We outline our own contributions to the field over several years, including concomitant strategies to furnish native peptide bonds and discuss the future directions of this field.

Synthesis through C(sp3)-C(sp2) Bond Scission in Alkenes and Ketones

ConspectusThe homolytic cleavage of C-C bonds adjacent to functional groups has recently become a popular strategy for restructuring the skeletons of complex organic molecules. In contrast to the traditional reactivity profiles of polar bond disconnections, homolytic scission furnishes carbon-centered free radicals primed for controlled termination with a diverse range of radicophiles. Beyond standard radical capture, transition-metal catalysis facilitates sophisticated C-C and C-heteroatom bond-forming reactions. Intensive efforts have been focused over many years into the cleavage of the neighboring C-C bonds of carboxylic acids and alcohols. Despite the ubiquity of alkenes and ketones in natural products, feedstock chemicals, and common synthetic intermediates, much less attention has been paid to exploiting their potential in diversifying chiral pool materials, such as terpenes and terpenoids. Defunctionalization in this manner is a powerful approach for synthesizing high-value chemicals and advanced synthetic intermediates because of the possibility to reconstruct and further decorate chirality-bearing carbon skeletons. Motivated by synthetic necessity, since 2018 our group has focused on developing ozonolysis-based dealkenylative molecular diversification, and we expanded into deacylation in 2025. In this Account, we chronicle our initial motivation, describe the historical background, and summarize our research into dealkenylative and deacylative synthesis. Our dealkenylative approach capitalizes on the ozonolysis of alkenes in MeOH to generate α-methoxyhydroperoxides primed for a reaction with reducing agents. Their reduction through single electron transfer, mediated by a transition metal, leads to the formation of an alkoxyl radical that undergoes rapid β-scission, furnishing both a carbon-centered free radical and an ester group derived from the acetal carbon atom. The produced free radical can be strategically terminated by radicophiles, thereby delivering remodeled chiral molecules. Using this concept, we have developed hydrodealkenylation (through hydrogen atom transfer from benzenethiol), dealkenylative thiylation (through thiyl group transfer from diaryl disulfides), alkenylation (through addition/elimination with nitrostyrenes), and oxodealkenylation (through treatment with TEMPO followed by oxidation). Furthermore, kinetic analysis has enabled the development of a catalytic FeII/vitamin C system for dealkenylative alkynylation and halodealkenylation. Synergizing ozonolysis and copper catalysis has recently enabled aminodealkenylation through net-redox-neutral C-C cleavage followed by C-N bond formation. Although the high oxidation potential of ozone relative to organic compounds makes alkene-to-peroxide conversion possible, it also limits the applicability of dealkenylative techniques for substrates featuring ozone-sensitive functional groups. We recently overcame this constraint by first applying Isayama-Mukayiama peroxidation to olefins and then using a novel catalytic system─catalytic FeIII and PhSH with stoichiometric γ-terpinene─for ozone-free hydrodealkenylation. Beyond alkenes, we have developed a straightforward methodology for the homolytic deacylative cleavage of ketones as well, including cycloalkanones. This process is applicable in total syntheses and in the late-stage modifications of complex ketone-containing natural products.

Photoredox-Catalyzed Hydroalkylation of C(sp3)-H Acids

We present a detailed study on a photoredox catalysis platform that directly engages 1,3-dicarbonyl C(sp3)-H acids toward radical reactions. This platform enables redox-neutral hydroalkylation and cross-coupling, as well as oxidative transformations that demonstrably improve on the prior state of the art. Herein, we present interrogations of the underlying catalytic cycle and mechanism for this platform through kinetic, thermodynamic, and computational studies. The present investigations also demonstrate the key role of lithium trifluoroacetate under complementary Ce-containing and Ce-free photoredox conditions to enable ligand-to-metal charge transfer (LMCT) or multi-site proton-coupled electron transfer (MS-PCET) activations, respectively.

Metal-Free Multicatalytic Decarbonylation of Aldehydes Driven by Light

A metal-free dual photo- and organocatalytic decarbonylation of aliphatic aldehydes is described for the first time. On the one hand, a wide range of tertiary aldehydes are smoothly decarbonylated thanks to the combination of thioxanthone as photocatalyst and diphenyl disulfide as organocatalyst. On the other hand, by simply using 4-CzIPN as photocatalyst instead of thioxanthone, various secondary aldehydes readily undergo decarbonylation in an orthogonal manner, via the in situ formation of 1,4-dihydropyridines. Both methodologies are compatible with various functional groups and are readily applied to the decarbonylation of complex molecules.

Photoredox-Catalyzed Radical Cyclization of Unactivated Alkene-Substituted β-Ketoesters Enabled Asymmetric Total Synthesis of Tricyclic Prostaglandin D2 Metabolite Methyl Ester

Regio- and stereoselective photoredox-catalyzed cyclizations of alkene-substituted β-ketoesters have been accomplished for the synthesis of polyfunctionalized cyclopentanones. This was achieved using 2,3,5,6-tetrakis(carbazol-9-yl)-1,4-dicyanobenzene (4CzTPN) and 2,4,6-triisopropyl-thiophenol as cocatalysts under illumination of a blue-light-emitting-diode at ambient temperature. The developed chemistry was successfully applied in the enantioselective total synthesis of the tricyclic prostaglandin D2 metabolite (tricyclic-PGDM) methyl ester, which was completed in 9 steps with an overall yield of 7%.

Metal Nanoclusters as Highly Efficient, Versatile Type-II Photoinitiators via Generating Radicals from Non-Conventional Hydrogen Donors

Development of highly efficient photocatalysis or photoinitiation systems that are applicable to various types of illumination source is critical to virtually all the light-driven applications. Here, we report a generalizable strategy to achieve highly sensitive, versatile photoinitiation systems based on the combination of metal nanoclusters with non-conventional hydrogen donors (co-initiators). Discovery of this type-II photoinitiation pathway in metal nanoclusters not only improves their two-photon initiation sensitivity by up to three-orders-of-magnitude, it further opens the door for metal nanoclusters to trigger the photopolymerization using the low-power UV light-emitting diodes. Different from molecular type-II photoinitiators, we found that the selection rules of hydrogen donors for metal nanoclusters are largely dependent on their ligand structures. More importantly, using electron paramagnetic resonance and mass spectroscopy, we for the first time demonstrate that the photoexcited metal nanoclusters can function as versatile hydrogen atom abstractors which generate various types of previously unreported thiyl and nitrogen-centered radicals. This finding indicates the broad opportunity of the future application of metal nanoclusters in light-driven organic synthesis and radical chemistry.

Transition-Metal-Free Radical Approach for the Synthesis of Isothiocyanates by Pyridinium 1,4-Zwitterionic Thiolates as a Sulfur Source

Herein, we disclose a novel, mild, transition-metal-free approach to synthesizing diversely functionalized isothiocyanates from the corresponding isocyanide precursors, achieving high to excellent yields (up to 97%). The current method sheds light on the reactivity of pyridinium 1,4-zwitterionic thiolates as an unprecedented sulfur source strikingly distinct from their previously known reactivity in ionic annulation reactions, showcasing an innovative approach to organic synthesis.

Dication Disulfuranes as Photoactivatable Sources of Radical Organocatalysts

The recent development of photoredox and energy transfer catalysis has led to a significant expansion of visible-light-driven chemical transformations. These methods have demonstrated exceptional efficiency in converting a wide range of substrates into radical intermediates and generating open-shell catalytic species. However, the simplification of catalytic systems and the direct generation of highly reactive radical organocatalysts through direct visible-light irradiation from stable precatalysts remains largely an unrealized goal. This challenge is mainly due to the limited availability of precatalysts that are responsive to visible light. Herein, we introduce a new class of bench-stable dicationic disulfuranes, which release highly reactive thiyl radicals upon blue-light excitation. Spectroscopic and computational studies reveal that this reactivity arises from a combination of structural features and intermolecular interactions. This family of molecules has been employed to catalyze radical cascades previously incompatible with photoredox conditions, enabling the efficient formation of 1,2-dioxolanes and 1,3-hydroxyketones in excellent yields and short reaction times.

Biomimetic thiyl radical formation from diphenyl disulfide with the low valent Ni(i) state of a cofactor F430 model

Cofactor F430 is a nickel-containing hydrocorphinato complex that plays important roles in the enzymatic formation and oxidation of methane. In methanotrophic bacteria, F430-dependent methyl-coenzyme M reductase (MCR) catalyses the endergonic conversion of the heterodisulfide adduct of coenzymes M and B with methane to methyl-coenzyme M and coenzyme B. In a radical mechanism, the Ni(i)-induced formation of a transient thiyl radical of coenzyme B from the heterodisulfide has been proposed. Herein, we introduce a new semi-artificial Ni-complex derived from vitamin B12 as functional model of F430. We demonstrate with electrochemical studies that the low valent Ni(i) complex cleaves the biomimetic model compound diphenyl disulfide into approx. 0.5 equivalents of thiophenol and a transient thiophenyl radical at a potential of -1.65 V vs. Fc/Fc+. Thiyl radicals are trapped in solution with phenylacetylene as thiophenyl-substituted olefins, but also lead to degradation of the Ni-complex.

Intramolecular Anti-Markovnikov Alkene Hydroaminative Cyclization to cis-2,3-Disubstituted Piperidines

Multisubstituted piperidines are prevalent units in pharmaceuticals. Herein, a photodriven anti-Markovnikov hydroaminative cyclization of a (Z)/(E)-isomeric mixture of trisubstituted alkenes using the lactate-derived C2-symmetric arylthiol catalyst was developed for the synthesis of cis-2,3-disubstituted piperidines and azepane in high diastereoselectivity and good yields. The origin of diastereoselectivity and the observed different hydroamination rate of alkene with different configurations were elucidated by the experimental and computational investigation.

Selective Synthesis of Vinyl Sulfides or 2-Methyl Benzothiazoles from Disulfides and CaC2 Mediated by a Trisulfur Radical Anion

In this report, we have established a novel and efficient method for selectively synthesizing either vinyl sulfides or 2-methylbenzothiazoles from the reaction of CaC2 and disulfides. The selective synthesis of these two distinct products can be controlled by simply adjusting the amount of K2S. The underlying reaction mechanism has been thoroughly investigated through control experiments, HRMS, and FTIR, which collectively support the pivotal role of a trisulfur radical anion. This radical species, generated in situ from K2S, is essential for the homolytic cleavage of the S-S bonds in a catalytic manner. Additionally, the trisulfur radical anion also acts as an effective mediator for activating the vinyl group of 2-aminophenyl vinyl sulfides, facilitating the crucial intramolecular cyclization required to produce 2-methylbenzothiazoles. Moreover, CaC2 not only serves as an acetylene source but also creates the basic conditions essential for the selective formation of vinyl sulfides. This methodology demonstrates broad substrate compatibility and excellent functional group tolerance, significantly enhancing its practical utility in diverse synthetic applications.

Halodealkenylation: Ozonolysis and Catalytic FeII with Vitamin C Convert C(sp3)-C(sp2) Bonds to C(sp3)-Halide Bonds

As part of our investigations into C-C bond scission and functionalization, we report a halodealkenylation in which the C(sp3)-C(sp2) bonds of alkenes are cleaved and C(sp3)-halide bonds are formed, via a radical intermediate. These transformations occur through Criegee ozonolysis and FeII-catalyzed reductive coupling assisted by vitamin C as a stoichiometric reductant. We applied this strategy to the formal synthesis of (R,R,R)-γ-tocopherol.

Photo Energy Transfer-Enabled Thiosulfinylation of Alkynes for Asymmetric Synthesis of Sultims

An asymmetric and highly practical thiosulfinylation of alkynes is established for the synthesis of sultim derivatives. The disclosed platform featured broad substrate scope and group tolerance for diverse biologically important molecules under mild and operationally simple conditions. Notably, the obtained chiral sulfinyl derivatives have demonstrated their potential application in further gram-scale synthesis and product derivatizations, providing a chance for drug discovery.

A Mild and Chemoselective Photoredox-Catalyzed Reduction of Aromatic Ketones

A mild, chemoselective reduction of aromatic ketones was discovered and investigated. The combination of photoredox and Lewis acid catalysis with an organic hydrogen source reduced aromatic ketones in good to high yield. Optimization found 2-phenylbenzothiazoline to be a sufficiently strong source of hydrogen in combination with an iridium photosensitizer and lanthanum triflate. Effective photomediated reduction of some substrates was also observed in the absence of photocatalyst and Lewis acid or with photocatalyst only. While yields were typically higher under catalytic conditions, some acid-sensitive substrates were more effectively reduced in the absence of Lewis acid. The reaction was generally high yielding, and chemoselecte, while tolerant of complex and functionally rich molecules.

Late-stage-functionalization of anti-depressant molecule buspirone

Buspirone, a well-established anxiolytic agent, has gained attention for its potential role as an antidepressant, primarily due to its unique pharmacological profile and the ability to modulate serotonin receptors effectively. Late-stage functionalization is considered as a pivotal strategy in drug synthesis that enhances the therapeutic efficacy of existing molecules. This review summarizes various late-stage functionalization techniques applicable to Buspirone, including photocatalyzed, metal-catalyzed, and enzyme-catalyzed reactions.

Photo-induced carboxylation of C(sp2)-S bonds in aryl thiols and derivatives with CO2

Aryl thiols have proven to be a useful class of electron donors and hydrogen atom sources in photochemical processes. However, the direct activation and functionalization of C(sp2)-S bonds in aryl thiols remains elusive in the field of photochemistry. Herein, a photochemical carboxylation of C(sp2)-S bonds in aryl thiols with CO2 is reported, providing a synthetic route to important aryl carboxylic acids. Moreover, different kinds of aryl thiol derivatives, benzeneselenol and diphenyl diselenide also show moderate-to-high reactivity in this transformation. Mechanistic studies, including DFT calculations, suggest that the in situ generated carbon dioxide radical anion (CO2•-) and disulfide might be the key intermediates, which undergo radical substitution to yield products. This reaction features mild and catalyst-free conditions, good functional group tolerance and wide substrate scope. Furthermore, the efficient degradation of polyphenylene sulfide highlights the usefulness of this methodology.

Aerobic Thiols Oxidative Coupling to Disulfides over Robust CoOx Nanoclusters Confined within Hierarchical Silicalite-1 Zeolite

Disulfide is an important organic reagent and synthetic intermediate that is widely used in organic synthesis, polymers, and other fields, but its synthesis still suffers from many environmental pollution and economic problems. Here, we present an environmentally friendly and efficient base-free aerobic oxidative thiol coupling catalyzed by heterogeneous CoOx nanoclusters entrapped in hierarchical silicalite-1 zeolite, synthesized by combining silane pore expansion and metal coordination methods under hydrothermal conditions. It is confirmed that open hierarchical channels favor mass diffusion, and the chemical valence of Co species in CoOx/h-S-1-H is +2, which is different from that of Co3O4 particles in CoOx/h-S-1-I. CoOx nanoclusters, are strongly fixed in the channels of silicalite-1 zeolite via Co-O-Si bonds, which is of great importance for the high catalytic activity in both symmetrical and unsymmetrical oxidative thiol coupling reactions. After recycling experiments four times, the CoOx/h-S-1-H used has almost the same chemical state and the same distribution of Co(II) species as the fresh catalysts. Based on DFT calculations and inhibition experiments, the oxidative coupling of thiols undergoes a free radical mechanism in which Co(III) causes RS-H cleavage into RS· and H· species. Subsequently, two RS· radicals are coupled to disulfides, while H· radicals react with the O species to form H2O molecules. This work not only provides guidance on catalyst design and parameter optimization for oxidative thiol coupling but also advances the understanding of the aerobic oxidation mechanism.

Polarity-Driven Thiyl Radical-Catalyzed Aerobic Debenzylation of Ethers and Amines

We report the use of a strongly electrophilic thiyl radical derived from commercially available pentafluorothiophenol as a demonstration of highly chemoselective H atom abstraction from electron-rich and relatively weak benzylic C-H bonds adjacent to the O and N atoms. This approach enables the selective oxidative removal of benzyl and p-methoxybenzyl groups from amines and ethers under ambient aerobic conditions.

Thiolate-mediated photoreduction and aerobic oxidation cycles in a bismuth-bismuth oxide nanosystem towards thiol-to-disulfide photocatalytic transformation

Bismuth(III) alkanethiolates [Bi(SR)3] formed by reacting Bi2O3 with alkanethiols (RSH) undergo a UV-blue light driven ligand-to-metal charge transfer photoreduction to disulfides and Bi colloids, which are then oxidised to Bi2O3 by dissolved oxygen and reconverted to Bi(SR)3 by RSH to prepare for the next Bi-Bi2O3 photoredox cycle, forming a basis for Bi(III)-catalysed thiol-to-disulfide conversion.

Building Catalytic Reactions One Electron at a Time

ConspectusClassical education in organic chemistry and catalysis, not the least my own, has centered on two-electron transformations, from nucleophilic attack to oxidative addition. The focus on two-electron chemistry is well-founded, as this brand of chemistry has enabled incredible feats of synthesis, from the development of life-saving pharmaceuticals to the production of ubiquitous commodity chemicals. With that said, this approach is in many ways complementary to the approach of nature, where enzymes frequently make use of single-electron "radical" steps to achieve challenging reactions with exceptional selectivity, including light detection and C-H hydroxylation. While the power of radical elementary steps is undeniable, the fundamental understanding of─and ability to apply─these in catalysis remains underdeveloped, constraining the palette with which chemists can make new reactions.Motivation to remedy this traditional underemphasis on radical catalysis has been intensified by the runaway success of outer-sphere photoredox catalysis, not only confirming the versatility of radicals in anthropogenic catalysis but also teaching the value of robust and well-understood catalytic cycles for reaction design. Indeed, I would argue the success of outer-sphere photoredox catalysis has been fueled by strong fundamental understanding of its underlying radical elementary steps, with consideration of single-electron transfer (SET) energetics allowing new reactions to be designed de novo with enviable confidence. However, outer-sphere photoredox catalysis is an outlier in this regard, with other mechanistic approaches remaining underexplored.Our research group is part of a growing movement to expand the vocabulary of synthetic radical catalysis beyond the traditional outer-sphere photoredox SET manifold, assembling new cycles comprised of hydrogen atom transfer (HAT), light-induced homolysis (LIH), and radical ligand transfer (RLT) steps in new combinations to achieve challenging transformations. These efforts have been made possible by the ever-growing understanding of these radical elementary steps and discovery of catalyst systems with significant mechanistic flexibility, most recently iron/thiol (Fe/S) cocatalysis.In this Account, I will focus on our efforts applying HAT and LIH steps in Fe/S cocatalysis, sharing broad guidelines we have found helpful for using these steps and demonstrating how they can be combined to make new reactions using three case studies: radical hydrogenation (HAT + HAT), decarboxylative protonation (LIH + HAT), and alkene hydrofluoroalkylation (LIH + HAT, with an intervening radical alkene addition). These efforts have highlighted the importance of several key parameters, including bond dissociation energy (BDE) and radical polarity, and I hope our findings similarly provide a valuable framework to others designing new radical catalytic reactions.

Photo-Clickable Triazine-Trione Thermosets as Promising 3D Scaffolds for Tissue Engineering Applications

There is an overwhelming demand for new scaffolding materials for tissue engineering (TE) purposes. Polymeric scaffolds have been explored as TE materials; however, their high glass transition state (Tg) limits their applicability. In this study, a novel materials platform for fabricating TE scaffolds is proposed based on solvent-free two-component heterocyclic triazine-trione (TATO) formulations, which cure at room temperature via thiol-ene/yne photochemistry. Three ester-containing thermosets, TATO-1, TATO-2, and TATO-3, are used for the fabrication of TE scaffolds including rigid discs, elastic films, microporous sponges, and 3D printed objects. After 14 days' incubation the materials covered a wide range of properties, from the soft TATO-2 having a compression modulus of 19.3 MPa and a Tg of 30.4 °C to the hard TATO-3 having a compression modulus of 411 MPa and a Tg of 62.5 °C. All materials exhibit micro- and nano-surface morphologies suited for bone tissue engineering, and in vitro studies found them all to be cytocompatible, supporting fast cell proliferation while minimizing cell apoptosis and necrosis. Moreover, bone marrow-derived mesenchymal stem cells on the surface of the materials are successfully differentiated into osteoblasts, adipocytes, and neuronal cells, underlining the broad potential for the biofabrication of TATO materials for TE clinical applications.

Cobalt-catalyzed hydrothiolation of alkynes for the diverse synthesis of branched alkenyl sulfides

Alkenyl sulfides have gained increasing prominence in medicinal chemistry and materials. Hydrothiolation of alkynes for the diverse synthesis of alkenyl sulfides is an appealing method. Herein, we report a cobalt-catalyzed Markovnikov hydromethylthiolation of alkynes to afford branched alkenyl methylsulfanes with good yields and high regioselectivity. This method also enables the diverse synthesis of branched alkenyl sulfides. The reaction shows good functional group tolerance and could be scaled up. The mechanistic studies including control experiments, deuterium-labeling experiments, and Hammett plot indicated alkynes insertion followed by electrophilic thiolation pathway.

Photochemical Initiation and Reactions of Thiyl Radicals Studied with SH2' Radical Traps

A radical trapping method based on an SH2' homolytic substitution reaction was applied to study the mechanism of a photochemical spirocyclisation of indole-ynones in the presence of thiols. Starting material, products and a range of trapped radical intermediates were simultaneously detected in reaction mixtures by mass spectrometry (MS). The trapped intermediates included both initiating and main chain propagating radicals. These data made it possible to propose a self-initiation mechanism consistent with the originally postulated photoexcitation of an intramolecular electron donor-acceptor complex of the substrate. The effect of thiol structure on the MS peak intensity of the reaction components was rationalised in terms of the relative stability of the radical intermediates. The results were compared to a simpler related reaction, a photochemical thiol-ene addition where reagents, products and trapped intermediate radicals were also detected by MS. Relative MS peak intensities were again explained by a combination of electronic and steric effects on the stability of intermediate radicals. Overall, SH2' radical trapping was demonstrated to be a powerful experimental technique for providing mechanistic evidence on photochemical and other organic radical reactions.

CdS Quantum Dot Gels as a Direct Hydrogen Atom Transfer Photocatalyst for C-H Activation

Here, we report CdS quantum dot (QD) gels, a three-dimensional network of interconnected CdS QDs, as a new type of direct hydrogen atom transfer (d-HAT) photocatalyst for C-H activation. We discovered that the photoexcited CdS QD gel could generate various neutral radicals, including α-amido, heterocyclic, acyl, and benzylic radicals, from their corresponding stable molecular substrates, including amides, thio/ethers, aldehydes, and benzylic compounds. Its C-H activation ability imparts a broad substrate and reaction scope. The mechanistic study reveals that this reactivity is intrinsic to CdS materials, and the neutral radical generation did not proceed via the conventional sequential electron transfer and proton transfer pathway. Instead, the C-H bonds are activated by the photoexcited CdS QD gel via a d-HAT mechanism. This d-HAT mechanism is supported by the linear correlation between the logarithm of the C-H bond activation rate constant and the C-H bond dissociation energy (BDE) with a Brønsted slope α=0.5. Our findings expand the currently limited direct hydrogen atom transfer photocatalysis toolbox and provide new possibilities for photocatalytic C-H activation.

Depolymerization of Native Lignin over Thiol Capped Ultrathin ZnIn2S4 Microbelts Mediated by Photogenerated Thiyl Radical

The valorization of native lignin to functionalized aromatic compounds under visible light is appealing yet challenging. In this communication, colloidal mercaptoalkanoic acid capped ultrathin ZnIn2S4 (ZIS) microbelts was successfully fabricated, which was used as a superior catalyst for depolymerization of native lignin in birch woodmeal under visible light, with an optimum yield of 28.8 wt % to functionalized aromatic monomers achieved in 8 h. The capped mercaptoalkanoic acid not only enables a solvent modulated reversible interchange of ZIS between the colloidal state for efficient reaction and the aggregated state for facile separation, but also serves as a precursor for light initiated generation of reactive thiyl radical for highly selective cleavage of β-O-4 bond in native lignin. This work provides a green and efficient strategy for the depolymerization of native lignin to functionalized aromatic monomers under mild conditions, which involves a new mechanism for the cleavage of β-O-4 bonds in native lignin. The capability of cleavage of β-O-4 bonds in native lignin by photogenerated thiyl radicals also demonstrates the great potential of using photogenerated thiyl radicals in organics transformations.

Recent Advances in Synthetic Methods by Photocatalytic Single-Electron Transfer Chemistry of Pyridine N-Oxides

By adoption of the enabling technology of modern photoredox catalysis and photochemistry, the generation of reactive and versatile pyridine N-oxy radicals can be facilely achieved from single-electron oxidation of pyridine N-oxides. This Synopsis highlights recent methodologies mediated by pyridine N-oxy radicals in developing (1) pyridine N-oxide-based hydrogen atom transfer catalysts for C(sp3)-H functionalizations and (2) β-oxyvinyl radical-mediated cascade reactions. In addition, recent research revealed that direct photoexcitation of pyridine N-oxides allowed for the generation of alkyl carbon radicals from alkylboronic acids.

A new mechanism of cancer initiation that involves the transformation of hepatocytes into preneoplastic single hepatocytes and minifoci positive for glutathione S-transferase P-form (GST-P) in rat livers: 3D analysis using a vibratome

BACKGROUND

Cancer initiation has long been "unknowable" in biology and medicine. In 1987, however, Moore and our research group observed single hepatocytes and minifoci that were strongly positive for glutathione S-transferase P-form (GST-P) in the rat liver as early as 2 to 3 days after initiation by diethylnitrosamine prior to the induction of GST-P+ foci and nodules. The induction of GST-P+ single hepatocytes, precursors of GST-P+ foci and nodules, was considered genetic. But, the details of the induction mechanism have remained unclear despite various examinations over a long period.

METHODS

Male Sprague-Dawley rats (aged 6 weeks) were fed a basal diet containing either benzyl isothiocyanate (BITC, 0.5% by wt) or 2-acetylaminofluorene (AAF, 0.04%) ad libitum for appropriate time intervals. All animals were anesthetized and euthanized. The livers obtained were excised, cut into 3- to 4-mm-thick slices and fixed in cold acetone at 4 °C. The liver specimens were then sliced into 25-µm-thick sections in PBS using an automated microtome (Vibratome 1500 Sectioning System, Vibratome Products, NY, USA). Immunocytochemical staining was performed in free solution, and the results were examined via digital light microscopy (Coolscope, Nikon, Tokyo).

RESULTS

3D analysis using a vibratome showed that GST-P is rapidly excreted into the bile of the liver of animals in response to strong carcinogenic stress caused by promoters or initiators. "Rapid biliary excretion of GST-P" was widely and commonly observed in all hepatocytes, GST-P+ single hepatocytes, minifoci, foci and nodules under appropriate conditions. Surprisingly, on the basis of these key findings, a new mechanism of cancer initiation involving the transformation of hepatocytes into GST-P+ single hepatocytes and minifoci in animal livers was identified. In addition, the initiation process was determined to be nongenetic because mutation is an invisible rare event.

CONCLUSIONS

This short review describes several details about breakthrough findings on cancer initiation in rat livers, the application of 3D analysis to other cancers and the importance in the genetic analysis in malignant diseases.

Reactions of alkynes with C-S bond formation: recent developments

Alkynes are important in organic synthesis. This review mainly focuses on recent advances (2013-2023) on alkynes with C-S bond formation, based on more than 30 types of sulfur reagents. The reactions of alkynes with various sulfur-containing compounds including RSSR (disulfides), RSH (thiols), S8 (elemental sulphur), alkynyl thioethers, RSCN, AgSCF3, K2S, Na2S, dithiane, RSCl, NFSI, RNCS, EtOCS2K, thiocarbamate, RSONH2, thiourea, sulfoxide, RSO2N3, CS2, RSO2NH2, RSO2NHNH2, RSO2Cl, RSO2Oar, RSO2SR', DABCO·(SO2)2, Na2S2O5, K2S2O5, RSO2H, RSO2Na and related compounds are discussed. Diverse mechanisms such as radical, electrophilic/nucleophilic addition, rearrangement, C-C bond cleavage, and CuAAC are discussed. The content is organized by substrates and reactivity patterns. We hope it will help in future research in this area.

Site-selective α-C(sp3)-H arylation of dialkylamines via hydrogen atom transfer catalysis-enabled radical aryl migration

Site-selective C(sp3)-H arylation is an appealing strategy to synthesize complex arene structures but remains a challenge facing synthetic chemists. Here we report the use of photoredox-mediated hydrogen atom transfer (HAT) catalysis to accomplish the site-selective α-C(sp3)-H arylation of dialkylamine-derived ureas through 1,4-radical aryl migration, by which a wide array of benzylamine motifs can be incorporated to the medicinally relevant systems in the late-stage installation steps. In contrast to previous efforts, this C-H arylation protocol exhibits specific site-selectivity, proforming predominantly on sterically more-hindered secondary and tertiary α-amino carbon centers, while the C-H functionalization of sterically less-hindered N-methyl group can be effectively circumvented in most cases. Moreover, a diverse range of multi-substituted piperidine derivatives can be obtained with excellent diastereoselectivity. Mechanistic and computational studies demonstrate that the rate-determining step for methylene C-H arylation is the initial H atom abstraction, whereas the radical ipso cyclization step bears the highest energy barrier for N-methyl functionalization. The relatively lower activation free energies for secondary and tertiary α-amino C-H arylation compared with the functionalization of methylic C-H bond lead to the exceptional site-selectivity.

Harnessing Bromo/Acyloxy Transposition (BrAcT) and Excited-State Copper Catalysis for Styrene Difunctionalization

1,2-Difunctionalization of styrenes, adding two distinct functional groups across the C═C double bond, has emerged as a powerful tool for enhancing molecular complexity. Herein, we report the development of a regioconvergent β-acyloxylation-α-ketonylation of styrenes through bromo/acyloxy transposition (BrAcT) and excited-state copper catalysis. This approach is amenable to gram-scale synthesis and tolerates a wide range of functional groups and complex molecular frameworks, including derivatives of natural products and marketed drugs. Our experimental and computational studies suggest a unique mechanism featuring a dynamic, ionic BrAcT process and excited-state copper-catalyzed redox reactions. We anticipate that this BrAcT process could serve as a broadly applicable and versatile strategy for β-acyloxylation-α-functionalization of styrenes, creating valuable intermediates for preparing new pharmaceuticals, agrochemicals, and functional materials.

Prognostic impact of concomitant pH-regulating drugs in patients with non-small cell lung cancer receiving epidermal growth factor receptor tyrosine kinase inhibitors: the Tokushukai REAl-world Data project 01-S1

PURPOSE

This study aimed to examine the prognostic impact of concomitant pH-regulating drug use in patients with epidermal growth factor receptor (EGFR)-mutation-positive non-small-cell lung cancer (NSCLC) receiving EGFR-tyrosine kinase inhibitors (TKIs).

METHODS

We conducted a nationwide retrospective cohort study and reviewed clinical data of consecutive patients with NSCLC treated with the first-line EGFR-TKIs in 46 hospitals between April 2010 and March 2020. Cox regression analyses were conducted to examine the differences in overall survival (OS) between patients treated with and without concomitant pH-regulating drugs, including potassium-competitive acid blockers (P-CABs), proton pump inhibitors (PPIs), and H2-receptor antagonists (H2RAs).

RESULTS

A total of 758 patients were included in the final dataset, of which 307 (40%) were administered concomitant pH-regulating drugs while receiving frontline EGFR-TKIs. After adjusting for basic patient characteristics, patients administered gefitinib, erlotinib, afatinib, and osimertinib with concomitant pH-regulating drugs had lower OS than those without concomitant pH-regulating drugs, with hazard ratios of 1.74 (with a 95% confidence interval of 1.34-2.27), 1.33 (0.80-2.22), 1.73 (0.89-3.36), and 5.04 (1.38-18.44), respectively. The 2-year OS rates of patients receiving gefitinib with or without concomitant pH-regulating drugs were 65.4 and 77.5%, those for erlotinib were 55.8 and 66.6%, and those for afatinib were 63.2 and 76.9%, respectively. The 1-year OS rates of patients receiving osimertinib with or without concomitant pH-regulating drugs were 88.1% and 96.9%, respectively.

CONCLUSION

In addition to the first-generation EGFR-TKIs, the second- and third-generation EGFR-TKIs also resulted in OS deterioration in patients with EGFR mutation-positive NSCLC when used concurrently with pH-regulating drugs.

Stabilized Carbon-Centered Radical-Mediated Carbosulfenylation of Styrenes: Modular Synthesis of Sulfur-Containing Glycine and Peptide Derivatives

Sulfur-containing amino acids and peptides play critical roles in organisms. Thiol-ene reactions between the thiol residues of L-cysteine and the alkenyl fragments in the designed coupling partners serve as primary tools for constructing C─S bonds in the synthesis of unnatural sulfur-containing amino acid derivatives. These reactions are favored due to the preference for hydrogen transfer from thiol to β-sulfanyl carbon radical intermediates. In this paper, the study proposes utilizing carbon-centered radicals stabilized by the capto-dative effect, generated under photocatalytic conditions from N-aryl glycine derivatives. The aim is to compete with the thiol hydrogen, enabling radical C─C bond formation with β-sulfanyl carbon radicals. This protocol is robust in the presence of air and water, offers significant potential as a modular and efficient platform for synthesizing sulfur-containing amino acids and modifying peptides, particularly with abundant disulfides and styrenes.

The sugar cube: Network control and emergence in stereoediting reactions

Stereochemical editing strategies have recently enabled the transformation of readily accessible substrates into rare and valuable products. Typically, site selectivity is achieved by minimizing kinetic complexity by using protecting groups to suppress reactivity at undesired sites (substrate control) or by using catalysts with tailored shapes to drive reactivity at the desired site (catalyst control). We propose "network control," a contrasting paradigm that exploits hidden interactions between rate constants to greatly amplify modest intrinsic biases and enable precise multisite editing. When network control is applied to the photochemical isomerization of hexoses, six of the eight possible diastereomers can be selectively obtained. The amplification effect can be viewed as a mesoscale phenomenon between the limiting regimes of kinetic control in simple chemical systems and metabolic regulation in complex biological systems.

Electrocatalytic Reduction of Disulfide Bonds across Chemical Modalities

The chemical properties of disulfides are leveraged in a wide array of applications, ranging from protein-drug conjugates for cancer treatment to self-healing materials. However, disulfide reduction strategies remain severely underdeveloped despite being the key to efficiently accessing the desired targets. Specifically, no homogeneous catalyst has been reported for this reaction, and conditions that allow the use of mild and green reductants (e.g., via electrochemical reduction) are not known. Herein, we unveil a vitamin B12-catalyzed, electrochemically driven protocol for efficiently reducing disulfide bonds in various aqueous buffers over a broad pH range. This robust and simple method is suitable for disulfide reductions of substrates ranging from small molecules to large proteins. Finally, one-pot reduction and conjugation of disulfide bonds in a monoclonal antibody were demonstrated to produce antibody conjugates.

p-Diarylboryl Halothiophenols as Multifunctional Catalysts via Photoactive Intramolecular Frustrated Lewis Pairs

p-Diarylboryl halothiophenols are developed and unequivocally characterized. Their photophysical properties and catalytic performance are unveiled by experimental and theoretical investigations. This novel class of triarylboranes behaves as a Brønsted acid to generate the corresponding borylthiophenolate that can absorb visible light to undergo intramolecular charge transfer to form a radical pair consisting of a boron radical anion and thiyl radical, which acts as a single-electron reductant while engaging in hydrogen atom transfer to regenerate the parent borylthiophenol. The synthetic relevance of this mode of action is demonstrated by the establishment of unique catalysis that integrates three different yet tunable functions in a single catalytic cycle, thereby allowing borylthiophenols to solely promote the assembly of sterically congested 1,2-diols and 1,2-aminoalcohol derivatives via radical-radical cross-coupling.

Synthesis of 4-Alkyl-2-chloro Imidazoles Using Intermolecular Radical Additions

Here, we report an intermolecular radical addition-based reaction sequence that permits preparation of functionalized imidazoles via a 5-step/3-pot procedure. In contrast to traditional, transition-metal mediated protocols, which generally provide access to 2-substituted imidazoles, the strategy described here allows incorporation of a structurally diverse range of complex alkyl side chains at the 4-position. This work demonstrates that intermolecular free-radical addition reactions are a powerful alternative to traditional methods used to synthesize medicinally important heterocyclic frameworks.

C(sp3)-H (N-Phenyltetrazole)thiolation as an Enabling Tool for Molecular Diversification

Methods enabling the broad diversification of C(sp3)-H bonds from a common intermediate are especially valuable in chemical synthesis. Herein, we report a site-selective (N-phenyltetrazole)thiolation of aliphatic and (hetero)benzylic C(sp3)-H bonds using a commercially available disulfide to access N-phenyltetrazole thioethers. The thioether products are readily elaborated in diverse fragment couplings for C-C, C-O, or C-N construction. The C-H functionalization proceeds via a radical-chain pathway involving hydrogen atom transfer by the electron-poor N-phenyltetrazolethiyl radical. Hexafluoroisopropanol was found to be essential to reactions involving aliphatic C(sp3)-H thiolation, with computational analysis consistent with dual hydrogen bonding of the N-phenyltetrazolethiyl radical imparting increased radical electrophilicity to facilitate the hydrogen atom transfer. Substrate is limiting reagent in all cases, and the reaction displays an exceptional functional group tolerance well suited to applications in late-stage diversification.

Redox Reactions of Organic Molecules Using Rotating Magnetic Field and Metal Rods

In recent years, redox reactions have harnessed light or mechanical energy to enable the formation of chemical bonds. We postulated a complementary approach that electromagnetic induction could promote the redox reaction of organic molecules using a rotating magnetic field and metal rods. Here, we report that electromotive force activates the redox-active trifluoromethylating reagents. This magnetoredox system can be applied to the trifluoromethylation of heteroarenes with high regioselectivity and hydrotrifluoromethylation of alkenes without the need for catalysts and organic additives.

Decyanative Heteroarylations of Glycine Derivatives

Amino acids and aromatic nitrogen heterocycles are widely used in pharmaceuticals. Herein, we present an effective visible-light-driven thiobenzoic acid (TBA)-catalyzed decyanative C(sp3)-H heteroarylation of glycine derivatives. This process occurs under mild and straightforward conditions, affording a range of valuable yet challenging-to-obtain α-heteroaryl amino acid derivatives. Moreover, this organocatalytic C(sp3)-C(sp2) bond formation reaction is applicable to the late-stage modification of various short peptides.

Radical Homopolymerization of Linear α-Olefins Enabled by 1,4-Cyano Group Migration

α-Olefins are valued and abundant building blocks from fossil resources. They are widely used to provide small-molecule or polymeric products. Despite numerous advantages of radical polymerization, it has been well-documented as textbook knowledge that α-olefins and their functionalized derivatives cannot be radically homopolymerized because of the degradative chain transfer side reactions. Herein, we report our studies on the homopolymerization of thiocyanate functionalized α-olefins enabled by 1,4-cyano group migration under radical conditions. By this approach, a library of ABC sequence-controlled polymers with high molecular weights can be prepared. We can also extend this strategy to the homopolymerization of α-substituted styrenic and acylate monomers which are known to be challenging to achieve. Overall, the demonstrated functional group migration radical polymerization could provide new possibilities to synthesize polymers with unprecedented main chain sequences and structures. These polymers are promising candidates for novel polymeric materials.

A Type of Chiral C2-Symmetric Arylthiol Catalyst for Highly Enantioselective Anti-Markovnikov Hydroamination

The development of chiral hydrogen donor catalysts is fundamental in the expansion and innovation of asymmetric organocatalyzed reactions via an enantioselective hydrogen atom transfer (HAT) process. Herein, an unprecedented type of chiral C2-symmetric arylthiol catalysts derived from readily available enantiomeric lactate ester was developed. With these catalysts, an asymmetric anti-Markovnikov alkene hydroamination-cyclization reaction was established, affording a variety of pharmaceutically interesting 3-substituted piperidines with moderate to high enantioselectivity. Results of the designed control experiments and theoretical computation rationalized the origin of stereocontrol and disclosed the spatial effect of the moiety of chiral thiols on the enantioselectivity. We believed the facile synthesis, flexible tunability, and effective enantioselectivity-controlling capability of these catalysts would shed light on the development of versatile chiral HAT catalysts and related asymmetric reactions.

Recent updates on vinyl cyclopropanes, aziridines and oxiranes: access to heterocyclic scaffolds

This present review delineates the repertoire of vinyl cyclopropanes and their stuctural analogues to accomplish a wide array of oxa-cycles, aza-cycles, and thia-cycles under transition metal catalysis and metal-free approaches from early 2019 to the present date. The generation of electrophilic π-allyl intermediates and 1-3/1-5-dipolarophile chemistry originating from VCPs are always green, step- and atom-economical and sustainable strategies in comparsion with prefunctionalized and/or C-H activation protocols. Here, the strained ring-system extends its applicability by relieving the strain to undergo a ring-expansion reaction to accomplish 5-9 membered carbo- and heterocyclic systems. The availability of chiral ligands in the ring-expansion reaction of VCPs and their analogues has paved the way to realizing asymmetric synthetic transformations.

Hypervalent Sulfur Derivatives as Sulfenylating Reagents: Visible-Light-Mediated Direct Thiolation of Activated C(sp2)-H Bonds with Dihalosulfuranes

In contrast to hypervalent iodine compounds, the chemistry of their sulfur analogues has been considerably less explored. Herein, we report the direct C-H bond thiolation of electron-rich heterocycles, arenes, and 1,3-dicarbonyls by dichlorosulfuranes under mild conditions. Mechanistic studies and density functional theory calculations suggest the radical chain mechanism of the disclosed transformation. The key to success is attributed to a strikingly low S-Cl bond dissociation energy, which enables the generation of radical species upon exposure to daylight.

Coumarin-Synthetic Methodologies, Pharmacology, and Application as Natural Fluorophore

Coumarins are secondary metabolites made up of benzene and α-pyrone rings fused together that can potentially treat various ailments, including cancer, metabolic, and degenerative disorders. Coumarins are a diverse category of both naturally occurring as well as synthesized compounds with numerous biological and therapeutic properties. Coumarins as fluorophores play a key role in fluorescent labeling of biomolecules, metal ion detection, microenvironment polarity detection, and pH detection. This review provides a detailed insight into the characteristics of coumarins as well as their biosynthesis in plants and metabolic pathways. Various synthetic strategies for coumarin core involving both conventional and green methods have been discussed comparing advantages and disadvantages of each method. Conventional methods discussed are Pechmann, Knoevenagel, Perkin, Wittig, Kostanecki, Buchwald-Hartwig, and metal-induced coupling reactions such as Heck and Suzuki, as well as green approaches involving microwave or ultrasound energy. Various pharmacological applications of coumarin derivatives are discussed in detail. The structural features and conditions responsible for influencing the fluorescence of coumarin core are also elaborated.

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.

Sulfur in Waste-Free Sustainable Synthesis: Advancing Carbon-Carbon Coupling Techniques

This review explores the pivotal role of sulfur in advancing sustainable carbon-carbon (C-C) coupling reactions. The unique electronic properties of sulfur, as a soft Lewis base with significant mesomeric effect make it an excellent candidate for initiating radical transformations, directing C-H-activation, and facilitating cycloaddition and C-S bond dissociation reactions. These attributes are crucial for developing waste-free methodologies in green chemistry. Our mini-review is focused on existing sulfur-directed C-C coupling techniques, emphasizing their sustainability and comparing state-of-the-art methods with traditional approaches. The review highlights the importance of this research in addressing current challenges in organic synthesis and catalysis. The innovative use of sulfur in photocatalytic, electrochemical and metal-catalyzed processes not only exemplifies significant advancements in the field but also opens new avenues for environmentally friendly chemical processes. By focusing on atom economy and waste minimization, the analysis provides broad appeal and potential for future developments in sustainable organic chemistry.

Screening seven-electron boron-centered radicals for dinitrogen activation

The activation of dinitrogen is significant as nitrogen-containing compounds play an important role in industries. However, the inert NN triple bond caused by its large HOMO-LUMO gap (10.8 eV) and high bond dissociation energy (945 kJ mol-1 ) renders its activation under mild conditions particularly challenging. Recent progress shows that a few main group species can mimic transition metal complexes to activate dinitrogen. Here, we demonstrate that a series of seven-electron (7e) boron-centered radical can be used to activate N2 via density functional theory calculations. It is found that boron-centered radicals containing amine ligand perform best on the thermodynamics of dinitrogen activation. In addition, when electron-donating groups are introduced at the boron atom, these radicals can be used to activate N2 with low reaction barriers. Further analysis suggests that the electron transfer from the boron atom to the π* orbitals of dinitrogen is essential for its activation. Our findings suggest great potential of 7e boron radicals in the field of dinitrogen activation.

Photochemical Transformations of Peptides Containing the N-(2-Selenoethyl)glycine Moiety

The diselenide bond has attracted considerable attention due to its ability to undergo the metathesis reaction in response to visible light. In our previous study, we demonstrated visible-light-induced diselenide metathesis of selenocysteine-containing linear peptides, allowing for the convenient generation of peptide libraries. Here, we investigated the transformation of linear and cyclic peptides containing the N-(2-selenoethyl)glycine moiety. The linear peptides were highly susceptible to the metathesis reaction, whereas the cyclic systems gave only limited conversion yields of the metathesis product. In both cases, side reactions leading to the formation of mono-, di-, and polyselenides were observed upon prolonged irradiation. To confirm the radical mechanism of the reaction, the radical initiator 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044) was tested, and it was found to induce diselenide metathesis without photochemical activation. The data were interpreted in the light of quantum-chemical simulations based on density functional theory (DFT). The simulations were performed at the B3LYP-D3BJ/def2-TZVP level of theory using a continuum solvation model (IEF-PCM) and methanol as a solvent.