Modular radical cross-coupling with sulfones enables access to sp3-rich (fluoro)alkylated scaffolds

Copper-Catalyzed Difluoromethylation of Alkyl Iodides Enabled by Aryl Radical Activation of Carbon-Iodine Bonds

The engagement of unactivated alkyl halides in copper-catalyzed cross-coupling reactions has been historically challenging, due to their low reduction potential and the slow oxidative addition of copper(I) catalysts. In this work, we report a novel strategy that leverages the halogen abstraction ability of aryl radicals, thereby engaging a diverse range of alkyl iodides in copper-catalyzed Negishi-type cross-coupling reactions at room temperature. Specifically, aryl radicals generated via copper catalysis efficiently initiate the cleavage of the carbon-iodide bonds of alkyl iodides. The alkyl radicals thus generated enter the copper catalytic cycles to couple with a difluoromethyl zinc reagent, thus furnishing the alkyl difluoromethane products. This unprecedented Negishi-type difluoromethylation approach has been applied to the late-stage modification of densely functionalized pharmaceutical agents and natural products.

Expeditious and Efficient ortho-Selective Trifluoromethane-sulfonylation of Arylhydroxylamines

A metal- and oxidant-free, practical and efficient method for the synthesis of highly versatile and synthetically useful ortho-trifluoromethanesulfonylated anilines from arylhydroxylamines and trifluoromethanesulfinic chloride was developed. This rapid transformation proceeded smoothly with good yields and excellent ortho-selectivity in the absence of any metals or ligands. Mechanistically, the reaction comprised a noncanonical O-trifluoromethanesulfinylation of the arylhydroxylamine, and the subsequent [2,3]-sigmatropic rearrangement to afford ortho-trifluoromethanesulfonylated aniline derivatives. The practical application of this reaction was demonstrated by further conversion into a series of functional molecules under different reaction conditions.

Synthesis of ArCF2X and [18F]Ar-CF3 via Cleavage of the Trifluoromethylsulfonyl Group

A versatile synthesis of ArCF₂X and [¹⁸F]Ar-CF₃ type compounds from readily available ArCF₂SO₂CF₃ has been developed. Diverse nucleophiles, including weak nucleophiles such as halides (¹⁸F^-, Cl^-, Br^-, and I^-), RSH, and ROH, could react with ArCF₂SO₂CF₃ efficiently to give the corresponding difluoromethylene products. The control experiments and the Hammett plot indicated that the reaction might proceed through a difluorocarbocation intermediate generated from the steric hindrance-assisted cleavage of the trifluoromethylsulfonyl group.

Selective synthesis of enol ethers via nickel-catalyzed cross coupling of α-oxy-vinylsulfones with alkylzinc reagents

We describe here a Ni-catalyzed Negishi coupling reaction to prepare 1,2-dialkyl enol ethers in a stereoconvergent fashion. This method employs readily available and bench-stable α-oxy-vinylsulfones as electrophiles. The C-sulfone bond in the α-oxy-vinylsulfone motif is cleaved chemoselectively in these reactions. The mild conditions are tolerant of a variety of functional groups on both partners, thus representing a general strategy for enol ether synthesis. This unique reactivity of α-oxy-vinylsulfones indicates their further application as electrophilic partners in cross-coupling reactions.

Electrochemical Intermolecular Monofluoroalkylation of α,β-Unsaturated Carboxylic Acids and Heteroaromatics with 2-Fluoromalonate Esters

An electrochemical approach for the preparation of monofluorides from α,β-unsaturated carboxylic acids and heteroaromatics with readily available 2-fluoromalonate esters as monofluoroalkyl radical precursors has been developed. The electrosynthesis employs ferrocene (Cp₂Fe) as a catalyst in a simple undivided cell with a broad substrate scope, which obviates the need for sacrificial oxidizing reagents.

Synthesis of Enantioenriched 3,4-Disubstituted Chromans through Lewis Base Catalyzed Carbosulfenylation

A method for the catalytic, enantioselective, carbosulfenylation of alkenes to construct 3,4-disubstituted chromans is described. Alkene activation proceeds through the intermediacy of enantioenriched, configurationally stable thiiranium ions generated from catalytic, Lewis base activation of an electrophilic sulfenylating agent. The transformation affords difficult-to-generate, enantioenriched, 3,4-disubstituted chromans in moderate to high yields and excellent enantioselectivities. A variety of substituents are compatible including electronically diverse functional groups as well as several functional handles such as aryl halides, esters, anilines, and phenols. The resulting thioether moiety is amenable to a number of functional group manipulations and transformations. Notably, the pendant sulfide was successfully cleaved to furnish a free thiol which readily provides access to most sulfur-containing functional groups which are present in natural products and pharmaceuticals.

Advances in [18F]Trifluoromethylation Chemistry for PET Imaging

Positron emission tomography (PET) is a preclinical and clinical imaging technique extensively used to study and visualize biological and physiological processes in vivo. Fluorine-18 (¹⁸F) is the most frequently used positron emitter for PET imaging due to its convenient 109.8 min half-life, high yield production on small biomedical cyclotrons, and well-established radiofluorination chemistry. The presence of fluorine atoms in many drugs opens new possibilities for developing radioligands labelled with fluorine-18. The trifluoromethyl group (CF₃) represents a versatile structural motif in medicinal and pharmaceutical chemistry to design and synthesize drug molecules with favourable pharmacological properties. This fact also makes CF₃ groups an exciting synthesis target from a PET tracer discovery perspective. Early attempts to synthesize [¹⁸F]CF₃-containing radiotracers were mainly hampered by low radiochemical yields and additional challenges such as low radiochemical purity and molar activity. However, recent innovations in [¹⁸F]trifluoromethylation chemistry have significantly expanded the chemical toolbox to synthesize fluorine-18-labelled radiotracers. This review presents the development of significant [¹⁸F]trifluoromethylation chemistry strategies to apply [¹⁸F]CF₃-containing radiotracers in preclinical and clinical PET imaging studies. The continuous growth of PET as a crucial functional imaging technique in biomedical and clinical research and the increasing number of CF₃-containing drugs will be the primary drivers for developing novel [¹⁸F]trifluoromethylation chemistry strategies in the future.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Transition-Metal-Catalyzed Monofluoroalkylation: Strategies for the Synthesis of Alkyl Fluorides by C-C Bond Formation

Alkyl fluorides modulate the conformation, lipophilicity, metabolic stability, and p K a of compounds containing aliphatic motifs and, therefore, have been valuable for medicinal chemistry. Despite significant research in organofluorine chemistry, the synthesis of alkyl fluorides, especially chiral alkyl fluorides, remains a challenge. Most commonly, alkyl fluorides are prepared by the formation of C-F bonds (fluorination), and numerous strategies for nucleophilic, electrophilic, and radical fluorination have been reported in recent years. Although strategies to access alkyl fluorides by C-C bond formation (monofluoroalkylation) are inherently convergent and complexity-generating, they have studied less than methods based on fluorination. This Review provides an overview of recent developments in the synthesis of chiral (enantioenriched or racemic) secondary and tertiary alkyl fluorides by monofluoroalkylation catalyzed by transition-metal complexes. We expect this contribution will illuminate the potential of monofluoroalkylations to simplify the synthesis of complex alkyl fluorides and suggest further research directions in this growing field.

Alkenylation and Arylation of Peptides via Ni-Catalyzed Reductive Coupling of α-C-Tosyl Peptides with Csp2 Triflates/Halides

A Ni-catalyzed reductive cross-coupling between α-C-tosyl peptides and Csp² triflates/halides has been developed. This protocol enables the formation of various unnatural di- and tripeptides containing vinyl and aryl side chains, and it expands the applications of Ni-catalyzed reductive cross-coupling in late-stage diversification of peptides.

A heavy-metal-free desulfonylative Giese-type reaction of benzothiazole sulfones under visible-light conditions

A visible-light-induced desulfonylative Giese-type reaction has been developed. Essential to the success is the employment of Hantzsch ester to activate benzothiazole sulfones without any heavy-metal additives. Not only benzylic benzothiazole sulfones but also alkyl ones were viable substrates and reacted with electron-deficient alkenes and a propiol amide.

Transition Metal-Catalyzed Cross-Couplings of Benzylic Sulfone Derivatives

In recent years, the use of organosulfones as a new class of cross-coupling partner in transition-metal catalyzed reactions has undergone significant advancement. In this personal account, our recent investigations into desulfonylative cross-coupling reactions of benzylic sulfone derivatives catalyzed by Pd, Ni, and Cu catalysis is described. Combined with the facile α-functionalizations of sulfones, our methods can be used to form valuable multiply-arylated structures such as di-, tri-, and, tetraarylmethanes from readily available substrates. The reactivity of sulfones can be increased by introducing electron-withdrawing substituents such as 3,5-bis(trifluoromethyl)phenyl and trifluoromethyl groups, which enable more challenging cross-coupling reactions. Reactive intermediates including Cu-carbene complexes were identified as key intermediates in sulfone activation, representing new types of C-SO₂ bond activation processes. These results indicate sulfones are powerful functional groups, enabling new catalytic desulfonylative transformations.

Copper-Mediated Cross-Coupling of Diazo Compounds with Sulfinates

A copper-mediated cross-coupling reaction between a diazo compound and a sodium alkane(arene)sulfinate gives a sulfone as the product. This reaction proceeds under mild conditions and features excellent functional group compatibility. A wide range of sodium alkane(arene)sulfinates were successfully applied in this chemistry. Mechanistic studies revealed that the overall reaction efficiency of the sulfinates was in line with their nucleophilicity in this reaction.

Synthetic exploration of sulfinyl radicals using sulfinyl sulfones

Sulfinyl radicals – one of the fundamental classes of S-centered radicals – have eluded synthetic application in organic chemistry for over 60 years, despite their potential to assemble valuable sulfoxide compounds. Here we report the successful generation and use of sulfinyl radicals in a dual radical addition/radical coupling with unsaturated hydrocarbons, where readily-accessed sulfinyl sulfones serve as the sulfinyl radical precursor. The strategy provides an entry to a variety of previously inaccessible linear and cyclic disulfurized adducts in a single step, and demonstrates tolerance to an extensive range of hydrocarbons and functional groups. Experimental and theoretical mechanistic investigations suggest that these reactions proceed through sequential sulfonyl and sulfinyl radical addition.

Sulfinyl radicals are an underexplored synthon in organic chemistry due to the fact that they reversibly add to pi systems and undergo homodimerization. Here the authors synthesize sulfonyl sulfones, previously thought to be unstable, and demonstrate their broad use as sulfinyl radical precursors in disulfurizations of alkenes and alkynes.

Nickel-Catalyzed Negishi-Type Arylation of Trialkylsulfonium Salts

Negishi-type arylation of trialkylsulfonium salts with arylzinc reagents has been accomplished under nickel catalysis. The use of cyclohexanethiol as an additional ligand was found to be particularly important to promote C–S cleavage. The present reaction accommodates one-pot arylation of dialkyl sulfides by combining with S-methylation with MeOTf. Mechanistic experiments suggest that C–S cleavage would proceed via single-electron transfer (SET) to generate the most stable carbon-centered radical and that the thiolate ligand would promote the C–S cleavage and radical recombination step.

Electrochemical reduction of fluoroalkyl sulfones for radical fluoroalkylation of alkenes

Radical fluoroalkylation of alkenes has been developed by electrochemical reduction of fluoroalkyl sulfones. A series of electron-deficient alkenes readily undergo hydrofluoroalkylation in good to excellent yields. This chemistry represents the first example of electrochemical generation of fluoroalkyl radicals from sulfones, which are used for practical radical fluoroalkylation of organic compounds.

Desulfonylative Electrocarboxylation with Carbon Dioxide

Electrocarboxylation of organic halides is one of the most investigated electrochemical approaches for converting thermodynamically inert carbon dioxide (CO₂) into value-added carboxylic acids. By converting organic halides into their sulfone derivatives, we have developed a highly efficient electrochemical desulfonylative carboxylation protocol. Such a strategy takes advantage of CO₂ as the abundant C1 building block for the facile preparation of multifunctionalized carboxylic acids, including the nonsteroidal anti-inflammatory drug ibuprofen, under mild reaction conditions.

Metal-catalysed C-Het (F, O, S, N) and C-C bond arylation

The formation of C-aryl bonds has been the focus of intensive research over the last decades for the construction of complex molecules from simple, readily available feedstocks. Traditionally, these strategies involve the coupling of organohalides (I, Br, Cl) with organometallic reagents (Mg, Zn, B, Si, Sn,…) such as Kumada-Corriu, Negishi, Suzuki-Miyaura, Hiyama and Sonogashira cross-couplings. More recently, alternative methods have provided access to these products by reactions with less reactive C-Het (F, O, S, N) and C-C bonds. Compared to traditional methods, the direct cleavage and arylation of these chemical bonds, the essential link in accessible feedstocks, has become increasingly important from the viewpoint of step-economy and functional-group compatibility. This comprehensive review aims to outline the development and advances of this topic, which was organized into (1) C-F bond arylation, (2) C-O bond arylation, (3) C-S bond arylation, (4) C-N bond arylation, and (5) C-C bond arylation. Substantial attention has been paid to the strategies and mechanistic investigations. We hope that this review can trigger chemists to discover more efficient methodologies to access arylation products by cleavage of these C-Het and C-C bonds.

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.

Iron-Catalyzed Fluoroalkylation of Arylborates with Sulfone Reagents: Beyond the Limitation of Reduction Potential

The iron-catalyzed alkyl-aryl coupling reaction between sulfones and arylboron compounds has remained a challenge. We report the first iron-catalyzed radical difluoroalkylation of arylborates with N-heteroaryl sulfones. The coordination between the iron catalyst and the nitrogen atom of N-heteroaryl sulfones was identified to be important in overcoming the reduction potential limitation of sulfones in the intermolecular single-electron-transfer process, which enables both fluoroalkyl N-heteroaryl sulfones (with relatively high reduction potentials) and nonfluorinated alkyl N-heteroaryl sulfones (with low reduction potentials) to serve as powerful alkylation reagents.

Cobalt-Catalyzed Hartung-Mukaiyama Cyclization of γ-Hydroxy Olefins: Stereocontrolled Synthesis of the Tetrahydrofuran Moiety of Amphidinolide N

Cobalt-catalyzed Mukaiyama-type cyclization of γ-hydroxy olefins is known as an atom- and step-economical means for stereoselective synthesis of 2,5-trans-substituted tetrahydrofuran derivatives. In this study, we investigated the synthesis of a series of 2,5-substituted tetrahydrofuran derivatives by means of a cobalt-catalyzed Hartung-Mukaiyama cyclization. The stereochemical consequence of the reaction was found to be largely dependent on the substitution pattern and relative configuration of γ-hydroxy olefins. 2,5-cis-Substituted tetrahydrofuran derivatives could be obtained diastereoselectively from appropriately substituted γ-hydroxy olefins. Additionally, relatively bulky olefin substituents and unprotected hydroxy groups at non-interfering positions (e.g., α and δ) were well tolerated in the reaction. Finally, the synthetic versatility of the Hartung-Mukaiyama cyclization was demonstrated through a stereocontrolled synthesis of the tetrahydrofuran moiety of amphidinolide N, a potent cytotoxic macrolide of marine origin. This study expands the capacity of Mukaiyama-type cyclization in that it can be used in convergent assembly of complex tetrahydrofuran motifs from internal olefins.

A Titanium-Catalyzed Reductive α-Desulfonylation

A titanium(III)-catalyzed desulfonylation gives access to functionalized alkyl nitrile building blocks from α-sulfonyl nitriles, circumventing traditional base-mediated α-alkylation conditions and strong single electron donors. The reaction tolerates numerous functional groups including free alcohols, esters, amides, and it can be applied also to the α-desulfonylation of ketones. In addition, a one-pot desulfonylative alkylation is demonstrated. Preliminary mechanistic studies indicate a catalyst-dependent mechanism involving a homolytic C-S cleavage.

Simple generation of various α-monofluoroalkyl radicals by organic photoredox catalysis: modular synthesis of β-monofluoroketones

A metal-free and operationally simple strategy for the generation of various α-monofluoroalkyl radicals has been developed. A combination of 1,4-bis(diarylamino)naphthalene photocatalyst and sulfoximine-based fluoroalkylating reagents is the key to success. The protocol can be applied to modular synthesis of β-monofluoroketones through radical monofluoroalkylation of alkenyl acetates.

Residual Solvent Signal of CDCl3 as a qNMR Internal Standard for Application in Organic Chemistry Laboratory

A nuclear magnetic resonance (NMR) spectrometer is a key instrument in the organic synthesis laboratory for structure determination, reaction control, and compound purity analysis. In addition to qualitative analysis, the application of NMR for quantitative analysis (qNMR) is gaining popularity. qNMR allows for simple quantification of crude product mixtures, determination of reaction yields, and purity of organic compounds. The determination of NMR yield requires the addition of an internal standard to each sample. Herein, we report a method where CDCl₃ residual solvent signal is used as an internal standard for qNMR after quantification in the solvent batch. This method significantly simplifies sample preparation and allows straightforward recovery of the analyte by the simple evaporation of the NMR solvent. The accuracy of the method is comparable to qNMR with 1,3,5-trimethoxybenzene as an internal standard if the herein described guidelines are followed.

Sequential C-F bond functionalizations of trifluoroacetamides and acetates via spin-center shifts

Defluorinative functionalization of readily accessible trifluoromethyl groups constitutes an economical route to partially fluorinated molecules. However, the controllable replacement of one or two fluorine atoms while maintaining high chemoselectivity remains a formidable challenge. Here we describe a general strategy for sequential carbon-fluorine (C-F) bond functionalizations of trifluoroacetamides and trifluoroacetates. The reaction begins with the activation of a carbonyl oxygen atom by a 4-dimethylaminopyridine-boryl radical, followed by a spin-center shift to trigger the C-F bond scission. A chemoselectivity-controllable two-stage process enables sequential generation of difluoro- and monofluoroalkyl radicals, which are selectively functionalized with different radical traps to afford diverse fluorinated products. The reaction mechanism and the origin of chemoselectivity were established by experimental and computational approaches.

Copper Catalyzed C(sp3)-H Bond Alkylation via Photoinduced Ligand-to-Metal Charge Transfer

Utilizing catalytic CuCl₂ we report the functionalization of numerous feedstock chemicals via the coupling of unactivated C(sp³)-H bonds with electron-deficient olefins. The active cuprate catalyst undergoes Ligand-to-Metal Charge Transfer (LMCT) to enable the generation of a chlorine radical which acts as a powerful hydrogen atom transfer reagent capable of abstracting strong electron-rich C(sp³)-H bonds. Of note is that the chlorocuprate catalyst is an exceedingly mild oxidant (0.5 V vs SCE) and that a proposed protodemetalation mechanism offers a broad scope of electron-deficient olefins, offering high diastereoselectivity in the case of endocyclic alkenes. The coupling of chlorine radical generation with Cu reduction through LMCT enables the generation of a highly active HAT reagent in an operationally simple and atom economical protocol.

Modern approaches towards the synthesis of geminal difluoroalkyl groups

This review will cover the importance of and most recent approaches toward geminal difluoroalkyl groups. Transition metal-mediated, photochemical, organocatalytic, and other methods as well as their mechanistic implications will be discussed, with special emphasis on applications to biologically-relevant compounds.

Nickel-Catalyzed Reductive 2-Pyridination of Aryl Iodides with Difluoromethyl 2-Pyridyl Sulfone

A novel nickel-catalyzed reductive cross-coupling between aryl iodides and difluoromethyl 2-pyridyl sulfone (2-PySO₂CF₂H) enables C(sp²)-C(sp²) bond formation through selective C(sp²)-S bond cleavage, which demonstrates the new reactivity of 2-PySO₂CF₂H reagent. This method employs readily available nickel catalyst and sulfones as cross-electrophile coupling partners, providing facile access to biaryls under mild reaction conditions without pregeneration of arylmetal reagents.

Synthesis of quaternary centres by single electron reduction and alkylation of alkylsulfones

A new method for the generation of tertiary radicals through single electron reduction of alkylsulfones promoted by Zn and 1,10-phenanthroline has been developed. These radicals could be employed in the Giese reaction, affording structurally diverse quaternary products in good yields. With the high modularity and functional group compatibility of sulfones, the utility of this method was demonstrated by intramolecular and iterative reactions to give complex structures. The radical generation process was investigated by control experiments and theoretical calculations.

A new method for the generation of tertiary radicals through single electron reduction of alkylsulfones promoted by Zn and 1,10-phenanthroline has been developed.

Residue-Selective Protein C-Formylation via Sequential Difluoroalkylation-Hydrolysis

The carbonyl group is now a widely useful, nonproteinogenic functional group in chemical biology, yet methods for its generation in proteins have relied upon either cotranslational incorporation of unnatural amino acids bearing carbonyls or oxidative conversion (chemical or enzymatic) of existing natural amino acids. If available, alternative strategies for directly adding the C=O group through C-C bond-forming C-carbonylation, particularly at currently inaccessible amino acid sites, would provide a powerful method for adding valuable reactivity and expanding possible function in proteins. Here, following a survey of methods for HCF₂· generation, we show that reductive photoredox catalysis enables mild radical-mediated difluoromethylation-hydrolysis of native protein residues as an effective method for carbonylation. Inherent selectivity of HCF₂· allowed preferential modification of Trp residues. The resulting C-2-difluoromethylated Trp undergoes Reimer-Tiemann-type dehalogenation providing highly effective spontaneous hydrolytic collapse in proteins to carbonylated HC(O)-Trp (C-formyl-Trp = CfW) residues. This new, unnatural protein residue CfW not only was found to be effective in bioconjugation, ligation, and labeling reactions but also displayed strong "red-shifting" of its absorption and fluorescent emission maxima, allowing direct use of Trp sites as UV-visualized fluorophores in proteins and even cells. In this way, this method for the effective generation of masked formyl-radical "HC(O)·" equivalents enables first examples of C-C bond-forming carbonylation in proteins, thereby expanding the chemical reactivity and spectroscopic function that may be selectively and post-translationally "edited" into biology.

Organic-photoredox-catalyzed three-component sulfonylative pyridylation of styrenes

An efficient, metal-free protocol for the three-component sulfonylative pyridylation of styrenes via organic-photoredox catalysis is described. This metal-free process enables the direct and selective installation of sulfonyl and heteroaryl motifs and tolerates a wide array of functional groups as well as complex molecular scaffolds, that could complement previous methods and would be of interest in pharmaceutical research.

An efficient, metal-free protocol for the three-component sulfonylative pyridylation of alkenes via organic-photoredox catalysis is described.

Late-stage difluoromethylation: concepts, developments and perspective

This review describes the conceptual advances that have led to the multiple difluoromethylation processes making use of well-defined CF₂H sources.

Using the Thiyl Radical for Aliphatic Hydrogen-Atom Transfer: Thiolation of Unactivated C-H Bonds

A metal- and catalyst-free thiyl-radical-mediated activation of alkanes is described. Tetrafluoropyridinyl disulfide is used to perform thiolation of the C-H bonds under irradiation with 400 nm light-emitting diodes. The key C-H activation step is believed to proceed via hydrogen-atom abstraction effected by the fluorinated thiyl radical. Secondary, tertiary, and heteroatom-substituted C-H bonds can be involved in the thiolation reaction. The resulting sulfides have wide potential as photoredox-active radical precursors in reactions with alkenes and heteroarenes.

Grignard-Reagent-Promoted Desulfonylation/Intramolecular Coupling for the Synthesis of 2-(1-Fluorovinyl)pyridines

A novel process involving Grignard-reagent-promoted desulfonylation/intramolecular coupling of readily available α-fluoro-α,β-unsaturated-(2-pyridyl)sulfones was realized that provided a series of polysubstituted 2-(1-fluorovinyl)pyridines in good yields. The intrinsic coordination between pyridine and Mg(II) along with the "negative fluorine effect" of the substrates should play the key role for the smooth transformation in the absence of transition-metal catalysts.

Integrating hydrogen production with anodic selective oxidation of sulfides over a CoFe layered double hydroxide electrode

Replacing the sluggish oxygen evolution reaction (OER) with oxidation reactions for the synthesis of complex pharmaceutical molecules coupled with enhanced hydrogen evolution reaction (HER) is highly attractive, but it is rarely explored. Here, we report an electrochemical protocol for selective oxidation of sulfides to sulfoxides over a CoFe layered double hydroxide (CoFe-LDH) anode in an aqueous-MeCN electrolyte, coupled with 2-fold promoted cathodic H2 productivity. This protocol displays high activity (85-96% yields), catalyst stability (10 cycles), and generality (12 examples) in selective sulfide oxidation. We demonstrate its applicability in the synthesis of four important pharmaceutical related sulfoxide compounds with scalability (up to 1.79 g). X-ray spectroscopy investigations reveal that the CoFe-LDH material evolved into amorphous CoFe-oxyhydroxide under catalytic conditions. This work may pave the way towards sustainable organic synthesis of valuable pharmaceuticals coupled with H2 production.

Alkyltriflones in the Ramberg-Bäcklund Reaction: An Efficient and Modular Synthesis of gem-Difluoroalkenes

The unprecedented synthesis of gem-difluoroalkenes through the Ramberg-Bäcklund reaction of alkyl triflones is described herein. Structurally diverse, fully substituted gem-difluoroalkenes that are difficult to prepare by other methods can be easily prepared from readily available triflones by treatment with specific Grignard reagents. Experimental and computational studies provide insight into the unique and critical role of the Grignard reagent, which serves both as a base to remove the α-proton and as a Lewis acid to assist C-F bond activation.

Photoredox Generation of Sulfonyl Radicals and Coupling with Electron Deficient Olefins

Various sulfone tetrazoles were activated via iridium photoredox catalysis in the presence of DMAP to give dialkyl sulfones. The presumed sulfone radical intermediates were trapped by a range of electron-deficient olefins in generally good to excellent yields.