Mechanistic Insight Enables Practical, Scalable, Room Temperature Chan–Lam N-Arylation of N-Aryl Sulfonamides

Computational Assessment of the Mechanistic Journey in Chan-Lam-Based Arylation of Imidazoles

Cu(II)-catalyzed C-N bond formation reactions remain one of most widely practiced and powerful protocols for the synthesis of value-added chemicals, bioactive molecules, and materials. Despite numerous experimental contributions, the overall mechanistic understanding of the C-N coupling reaction based on the Chan-Lam (CL) reaction methodology is still limited and underdeveloped, particularly with respect to the use of different substrates and catalytic species. Herein, we report an in-depth DFT-based study on the mechanism of N-arylation of imidazoles following Collman's experimental setup. Our findings unfold for the first time the ligand-based CL coupling catalyzed by the [Cu(II)(OH)TMEDA]2Cl2 complex. The transmetalation step with an energy span of 26.2 kcal mol-1 is rate-determining, while the subsequent disproportionation and reductive elimination are relatively facile (δE = 16.4 kcal mol-1) in comparison to the CL amination of secondary amines. The final oxidative catalyst regeneration results in the presence of O2, accompanying an energy span of 12.8 kcal mol-1, where hydrogen transfer from the coordinated water allows the reduction of superoxo linkage. Couplings performed in the presence of a combination of bidentate sp3-N ligands with single and double -(CH2)- spacer units afford a kinetically facile transformation (24.5 kcal mol-1). Furthermore, our results agree with the experimental outcomes of regioselective couplings of substituted imidazoles.

An Organocopper(III) Fluoride Triggering C-CF3 Bond Formation

Copper(III) fluorides are catalytically competent, yet elusive, intermediates in cross-coupling. The synthesis of [PPh4 ][CuIII (CF3 )3 F] (2), the first stable (isolable) CuIII -F, was accomplished via chloride addition to [CuIII (CF3 )3 (py)] (1) yielding [PPh4 ][CuIII (CF3 )3 Cl(py)] (1⋅Cl), followed by treatment with AgF. The CuIII halides 1⋅Cl and 2 were fully characterized using nuclear magnetic resonance (NMR) spectroscopy, single crystal X-ray diffraction (Sc-XRD) and elemental analysis (EA). Complex 2 proved capable of forging C-CF3 bonds from silyl-capped alkynes. In-depth mechanistic studies combining probes, theoretical calculations, trapping of intermediate 4a ([PPh4 ][CuIII (CF3 )3 (C≡CPh)]) and radical tests unveil the key role of the CuIII acetylides that undergo facile 2e- reductive elimination furnishing the trifluoromethylated alkynes (RC≡CCF3 ), which are industrially relevant synthons in drug discovery, pharma and agrochemistry.

Mechanistic Avenues in the Chan-Lam-Based Etherification Reaction: A Computational Exploration

Ongoing advances in CuII -catalyzed aerobic oxidative coupling reactions between arylboronic esters and diverse heteroatom nucleophiles have strengthened the development of the general Chan-Lam (CL)-based reaction protocol, including C-O bond formation methodologies. In-depth mechanistic understanding of CL etherification with specific emphasis on different reaction routes and their energetics are still lacking, even though the reaction has been experimentally explored. Here, we present a DFT-guided computational study to unravel the mechanistic pathways of CL-based etherification. The computational findings provide some interesting insights into the fundamental steps of the catalytic cycle, particularly the rate-determining transmetalation event. An aryl boronic ester-coordinated, methoxide-bridged CuII intermediate that acts as resting state undergoes transmetalation with an activation barrier of 20.4 kcal mol-1 . The energy spans of the remaining fundamental steps leading to the methoxylated product are relatively low. The minor p-cresol product requires an additional 14.2 kcal mol-1 energy span to surmount in comparison to the favored route. Hammett studies for the substituted aryl boronic esters reveal higher reaction turnovers for electron-rich aryl systems. The results agree with previously reported spectroscopic and kinetic observations. For a series of alcohol substrates, it was observed that, except for cyclohexanol, moderate to high etherification turnovers are predicted.

Photocatalytic C-N bond construction toward high-value nitrogenous chemicals

The construction of carbon-nitrogen bonds is vital for producing versatile nitrogenous compounds for the chemical and pharmaceutical industries. Among developed synthetic approaches to nitrogenous chemicals, photocatalysis is particularly prominent and has become one of the emerging fields due to its unique advantages of eco-sustainable characteristics, efficient process integration, no need for high-pressure H2, and tunable synthesis methods for developing advanced photocatalytic materials. Here, the review focuses on potential photocatalytic protocols developed for the construction of robust carbon-nitrogen bonds in discrepant activation environments to produce high-value nitrogenous chemicals. The photocatalytic C-N bond construction strategies and involved reaction mechanisms are elucidated.

Copper Complexes with N,N,N-Tridentate Quinolinyl Anilido-Imine Ligands: Synthesis and Their Catalytic Application in Chan-Lam Reactions

The treatment of 2-(ArNC(H))C6H4-HNC9H6N with n-BuLi and the subsequent addition of CuCl2 afforded the anilido-aldimine Cu(II) complexes 1-5 Cu[{2-[ArN=C(H)]C6H4}N(8-C9H6N)]Cl (Ar = 2,6-iPr2C6H3 (1), 2,4,6-(CH3)3C6H2 (2), 4-OCH3C6H4 (3), 4-BrC6H4 (4), 4-ClC6H4 (5)), respectively. All the copper complexes were fully characterized by IR, EPR and HR-MS spectra. The X-ray diffraction analysis reveals that 2 and 4 are mononuclear complexes, and the Cu atom is sitting in a slightly square-planar geometry. These Cu(II) complexes have exhibited excellent catalytic activity in the Chan-Lam coupling reactions of benzimidazole derivatives with arylboronic acids, achieving the highest yields of up to 96%.

A Chemoselective Polarity-Mismatched Photocatalytic C(sp3 )-C(sp2 ) Cross-Coupling Enabled by Synergistic Boron Activation

We report the development of a C(sp3 )-C(sp2 ) coupling reaction using styrene boronic acids and redox-active esters under photoredox catalysis. The reaction proceeds through an unusual polarity-mismatched radical addition mechanism that is orthogonal to established processes. Synergistic activation of the radical precursor and organoboron are critical mechanistic events. Activation of an N-hydroxyphthalimide (NHPI) ester by coordination to boron enables electron transfer, with decomposition leading to a nucleofuge rebound, activating the organoboron to radical addition. The unique mechanism enables chemoselective coupling of styrene boronic acids in the presence of other alkene radical acceptors. The scope and limitations of the reaction, and a detailed mechanistic investigation are presented.

Exploiting Coordination Behavior of 7-Azaindole for Mechanistic Investigation of Chan-Lam Coupling and Application to 7-Azaindole Based Pharmacophores

Multiple spectroscopic techniques, along with single-crystal X-ray analysis, have been used to reveal the detailed structural and electronic information on reaction intermediates of a new copper(II)-DBU catalytic system for the N-arylation of 7-Azaindole. The reaction mixture of Chan-Lam cross-coupling yields two dimeric copper(II)-7-azaindole complexes, including one attached with DBU, prior to adding arylboronic acid and are confirmed structurally and spectroscopically. A suitable mechanism has been proposed using the dimeric copper(II) complex as a catalyst for the coupling reactions. The role of DBU as a base and also as an auxiliary ligand in the course of the reaction has been established. The transmetalated monomeric aryl-copper(II) species generated from the dimeric unit is oxidized by another equivalent of copper(II) to yield an aryl-copper(III) intermediate for facile N-arylation, which has been authenticated with UV-vis spectroscopy. The regeneration of the copper(II)-catalyst by aerial oxidation of colorless copper(I) species (generated via reductive elimination and disproportionation step) is confirmed by mass and absorption spectroscopy. Detailed DFT and TD-DFT calculations help to rationalize the proposed reaction intermediates and their corresponding electronic transitions. Moreover, the confirmation of copper(I)-7-azaindole intermediate via HRMS reaffirmed the involvement of Cu(II)/Cu(III)/Cu(I) species in the Chan-Lam type of coupling. A medicinally-important 7-azaindole-based SHP2 inhibitor has been synthesized via sequential arylation.

CuF2/DMAP-Catalyzed N-Vinylation: Scope and Mechanistic Study

CuF₂/DMAP has been established as an excellent catalytic system for vinylsilane-promoted N-vinylation of amides and azoles at room temperature without an external fluoride source. A mechanism has been proposed on the basis of the isolation of reactive intermediate [Cu(DMAP)₄Cl₂], fluoride ion-assisted transmetalation, and ultraviolet-visible spectroscopic studies. The catalytic efficiency of the synthesized and structurally characterized [Cu(DMAP)₄Cl₂] complex has been demonstrated. The valuable monomers for water-soluble polymers, viz., NVP, NVC, and NVIBA, were synthesized on a gram scale.

Copper-Catalyzed Homocoupling of Boronic Acids: A Focus on B-to-Cu and Cu-to-Cu Transmetalations

Controlling and understanding the Cu-catalyzed homocoupling reaction is crucial to prompt the development of efficient Cu-catalyzed cross-coupling reactions. The presence of a coordinating base (hydroxide and methoxide) enables the B-to-Cu(II) transmetalation from aryl boronic acid to CuIICl2 in methanol, through the formation of mixed Cu-(μ-OH)-B intermediates. A second B-to-Cu transmetalation to form bis-aryl Cu(II) complexes is disfavored. Instead, organocopper(II) dimers undergo a coupled transmetalation-electron transfer (TET) allowing the formation of bis-organocopper(III) complexes readily promoting reductive elimination. Based on this mechanism some guidelines are suggested to control the undesired formation of homocoupling product in Cu-catalyzed cross-coupling reactions.

Molecular Decomposition Routes of Diaryl Diselenide Precursors in Relation to the Phase Determination of Copper Selenides

¹H nuclear magnetic resonance (NMR), ⁷⁷Se NMR, and powder X-ray diffraction (XRD) were used to monitor the thermal decomposition of diphenyl and dibenzyl diselenide precursors toward the synthesis of copper selenides. Copper was found to promote the decomposition of both precursors. The inorganic nanocrystals and organic byproducts were sensitive to the specific diaryl diselenides and the presence of oleylamine and copper. Molecular mechanistic routes are proposed. Berzelianite (Cu_1.8Se), klockmannite (CuSe), umangite (Cu₃Se₂), and both petřı́čekite (m-CuSe₂) and krutaite (p-CuSe₂) were identified as products. Multistep transformations between phases were discovered through reactions with the organoselenium precursors, and organic decomposition products are proposed.

Ni(cod)(duroquinone)-Catalyzed C-N Cross-Coupling for the Synthesis of N,N-Diarylsulfonamides

We report a C-N cross-coupling reaction of weakly nucleophilic N-arylsulfonamides and aryl bromides to access N,N-diarylsulfonamides using Ni(cod)(DQ) as a catalyst without additional ligands. The process is compatible with electron-deficient and electron-rich aryl and heteroaryl bromides (34 examples, 21-98%) and can be applied to the derivatization of an N-arylsulfonamide pharmaceutical compound.

Metal-catalyzed reactions for the C(sp2)–N bond formation: achievements of recent years

The review deals with the main catalytic methods for the C(sp2)–N bond formation, including Buchwald–Hartwig palladium-catalyzed amination of aryl and heteroaryl halides, renaissance of the Ullmann chemistry, i.e., the application of catalysis by copper complexes to form the carbon–nitrogen bond, and Chan–Lam reactions of (hetero)arylboronic acids with amines. Also, oxidative amination with C–H activation, which has been booming during the last decade, is addressed. Particular attention is paid to achievements in the application of heterogenized catalysts.

The bibliography includes 350 references.

Unified Approach to Benzo[d]thiazol-2-yl-Sulfonamides

In this paper, we report a unified approach to N-substituted and N,N-disubstituted benzothiazole (BT) sulfonamides. Our approach to BT-sulfonamides starts from simple commercially available building blocks (benzo[d]thiazole-2-thiol and primary and secondary amines) that are connected via (a) a S oxidation/S-N coupling approach, (b) a S-N coupling/S-oxidation sequence, or via (c) a S-oxidation/S-F bond formation/SuFEx approach. The labile N-H bond in N-monoalkylated BT-sulfonamides (pK_a (BTSO₂N(H)Bn) = 3.34 ± 0.05) further allowed us to develop a simple weak base-promoted N-alkylation method and a stereoselective microwave-promoted Fukuyama-Mitsunobu reaction. N-Alkyl-N-aryl BT-sulfonamides were accessed with the help of the Chan-Lam coupling reaction. Developed methods were further used in stereo and chemoselective transformations of podophyllotoxin and several amino alcohols.

Direct, Late-Stage Mono-N-arylation of Pentamidine: Method Development, Mechanistic Insight, and Expedient Access to Novel Antiparastitics against Diamidine-Resistant Parasites

A selective mono‐N‐arylation strategy of amidines under Chan‐Lam conditions is described. During the reaction optimization phase, the isolation of a mononuclear Cu(II) complex provided unique mechanistic insight into the operation of Chan‐Lam mono‐N‐arylation. The scope of the process is demonstrated, and then applied to access the first mono‐N‐arylated analogues of pentamidine. Sub‐micromolar activity against kinetoplastid parasites was observed for several analogues with no cross‐resistance in pentamidine and diminazene‐resistant trypanosome strains and against Leishmania mexicana. A fluorescent mono‐N‐arylated pentamidine analogue revealed rapid cellular uptake, accumulating in parasite nuclei and the kinetoplasts. The DNA binding capability of the mono‐N‐arylated pentamidine series was confirmed by UV‐melt measurements using AT‐rich DNA. This work highlights the potential to use Chan‐Lam mono‐N‐arylation to develop therapeutic leads against diamidine‐resistant trypanosomiasis and leishmaniasis.

A Dicopper Nitrenoid by Oxidation of a CuICuI Core: Synthesis, Electronic Structure, and Reactivity

A dicopper nitrenoid complex was prepared by formal oxidative addition of the nitrenoid fragment to a dicopper(I) center by reaction with the iminoiodinane PhINTs (Ts = tosylate). This nitrenoid complex, (DPFN)Cu₂(μ-NTs)[NTf₂]₂ (DPFN = 2,7-bis(fluorodi(2-pyridyl)methyl)-1,8-naphthyridine), is a powerful H atom abstractor that reacts with a range of strong C-H bonds to form a mixed-valence Cu(I)/Cu(II) μ-NHTs amido complex in the first example of a clean H atom transfer to a dicopper nitrenoid core. In line with this reactivity, DFT calculations reveal that the nitrenoid is best described as an iminyl (NR radical anion) complex. The nitrenoid was trapped by the addition of water to form a mixed-donor hydroxo/amido dicopper(II) complex, which was independently obtained by reaction of a Cu₂(μ-OH)₂ complex with an amine through a protonolysis pathway. This mixed-donor complex is an analogue for the proposed intermediate in copper-catalyzed Chan-Evans-Lam coupling, which proceeds via C-X (X = N or O) bond formation. Treatment of the dicopper(II) mixed donor complex with MgPh₂(THF)₂ resulted in generation of a mixture that includes both phenol and a previously reported dicopper(I) bridging phenyl complex, illustrating that both reduction of dicopper(II) to dicopper(I) and concomitant C-X bond formation are feasible.

Mediator-Enabled Electrocatalysis with Ligandless Copper for Anaerobic Chan-Lam Coupling Reactions

Simple copper salts serve as catalysts to effect C-X bond-forming reactions in some of the most utilized transformations in synthesis, including the oxidative coupling of aryl boronic acids and amines. However, these Chan-Lam coupling reactions have historically relied on chemical oxidants that limit their applicability beyond small-scale synthesis. Despite the success of replacing strong chemical oxidants with electrochemistry for a variety of metal-catalyzed processes, electrooxidative reactions with ligandless copper catalysts are plagued by slow electron-transfer kinetics, irreversible copper plating, and competitive substrate oxidation. Herein, we report the implementation of substoichiometric quantities of redox mediators to address limitations to Cu-catalyzed electrosynthesis. Mechanistic studies reveal that mediators serve multiple roles by (i) rapidly oxidizing low-valent Cu intermediates, (ii) stripping Cu metal from the cathode to regenerate the catalyst and reveal the active Pt surface for proton reduction, and (iii) providing anodic overcharge protection to prevent substrate oxidation. This strategy is applied to Chan-Lam coupling of aryl-, heteroaryl-, and alkylamines with arylboronic acids in the absence of chemical oxidants. Couplings under these electrochemical conditions occur with higher yields and shorter reaction times than conventional reactions in air and provide complementary substrate reactivity.

Oxidative cross-coupling processes inspired by the Chan-Lam reaction

The Cu-catalyzed oxidative cross-coupling of N- and O-nucleophiles with aryl boronic acids (the Chan-Lam reaction) remains among the most useful approaches to prepare aniline and phenol derivatives. The combination of high chemoselectivity, mild reaction conditions, and the ability to use simple Cu-salts as catalysts makes this process a valuable alternative to aromatic substitutions and Pd-catalyzed reactions of aryl electrophiles (Buchwald-Hartwig coupling). Despite the widespread use of Chan-Lam reactions in synthesis, the analogous carbon-carbon bond forming variant of this process had not been developed prior to our work. This feature article describes our discovery and application of Cu-catalyzed oxidative coupling reactions of activated methylene derivatives or carboxylic acids with nucleophiles including aryl boronic esters and amines.

Aerobic Copper-Catalyzed Salicylaldehydic Cformyl -H Arylations with Arylboronic Acids

We report a challenging copper-catalyzed C_formyl -H arylation of salicylaldehydes with arylboronic acids that involves unique salicylaldehydic copper species that differ from reported salicylaldehydic rhodacycles and palladacycles. This protocol has high chemoselectivity for the C_formyl -H bond compared to the phenolic O-H bond involving copper catalysis under high reaction temperatures. This approach is compatible with a wide range of salicylaldehyde and arylboronic acid substrates, including estrone and carbazole derivatives, which leads to the corresponding arylation products. Mechanistic studies show that the 2-hydroxy group of the salicylaldehyde substrate triggers the formation of salicylaldehydic copper complexes through a Cu^I /Cu^II /Cu^III catalytic cycle.

Autocatalytic photoredox Chan-Lam coupling of free diaryl sulfoximines with arylboronic acids

N-Arylation of NH-sulfoximines represents an appealing approach to access N-aryl sulfoximines, but has not been successfully applied to NH-diaryl sulfoximines. Herein, a copper-catalyzed photoredox dehydrogenative Chan-Lam coupling of free diaryl sulfoximines and arylboronic acids is described. This neutral and ligand-free coupling is initiated by ambient light-induced copper-catalyzed single-electron reduction of NH-sulfoximines. This electron transfer route circumvents the sacrificial oxidant employed in traditional Chan-Lam coupling reactions, increasing the environmental friendliness of this process. Instead, dihydrogen gas forms as a byproduct of this reaction. Mechanistic investigations also reveal a unique autocatalysis process. The C–N coupling products, N-arylated sulfoximines, serve as ligands along with NH-sulfoximine to bind to the copper species, generating the photocatalyst. DFT calculations reveal that both the NH-sulfoximine substrate and the N-aryl product can ligate the copper accounting for the observed autocatalysis. Two energetically viable stepwise pathways were located wherein the copper facilitates hydrogen atom abstraction from the NH-sulfoximine and the ethanol solvent to produce dihydrogen. The protocol described herein represents an appealing alternative strategy to the classic oxidative Chan-Lam reaction, allowing greater substrate generality as well as the elimination of byproduct formation from oxidants.

N-Arylation of NH-diaryl sulfoximines faces synthetic challenges among reported methods. Here, the authors present a mild copper-catalyzed photoredox dehydrogenative Chan-Lam coupling of free diaryl sulfoximines and arylboronic acids via an auto-catalytic process.

Advances in Carbon–Element Bond Construction under Chan–Lam Cross-Coupling Conditions: A Second Decade

Copper-mediated carbon–heteroatom bond-forming reactions involving a wide range of substrates have been in the spotlight for many organic chemists. This review highlights developments between 2010 and 2019 in both stoichiometric and catalytic copper-mediated reactions, and also examples of nickel-mediated reactions, under modified Chan–Lam cross-coupling conditions using various nucleophiles; examples include chemo- and regioselective N-arylations or O-arylations. The utilization of various nucleophiles as coupling partners together with reaction optimization (including the choice of copper source, ligands, base, and other additives), limitations, scope, and mechanisms are examined; these have benefitted the development of efficient and milder methods. The synthesis of medicinally valuable or pharmaceutically important nitrogen heterocycles, including isotope-labeled compounds, is also included. Chan–Lam coupling reaction can now form twelve different C–element bonds, making it one of the most diverse and mild reactions known in organic chemistry.

1 Introduction

2 Construction of C–N and C–O Bonds

2.1 C–N Bond Formation

2.1.1 Original Discovery via Stoichiometric Copper-Mediated C–N Bond Formation

2.1.2 Copper-Catalyzed C–N Bond Formation

2.1.3 Coupling with Azides, Sulfoximines, and Sulfonediimines as Nitrogen­ Nucleophiles

2.1.4 Coupling with N,N-Dialkylhydroxylamines

2.1.5 Enolate Coupling with sp3-Carbon Nucleophiles

2.1.6 Nickel-Catalyzed Chan–Lam Coupling

2.1.7 Coupling with Amino Acids

2.1.8 Coupling with Alkylboron Reagents

2.1.9 Coupling with Electron-Deficient Heteroarylamines

2.1.10 Selective C–N Bond Formation for the Synthesis of Heterocycle-Containing Compounds

2.1.11 Using Sulfonato-imino Copper(II) Complexes

2.2 C–O Bond Formation

2.2.1 Coupling with (Hetero)arylboron Reagents

2.2.2 Coupling with Alkyl- and Alkenylboron Reagents

3 C–Element (Element = S, P, C, F, Cl, Br, I, Se, Te, At) Bond Forma tion under Modified Chan–Lam Conditions

4 Conclusions

Copper-Catalyzed Oxidative Acetalization of Boronic Esters: An Umpolung Strategy for Cyclic Acetal Synthesis

A protocol for the acetalization of boronic esters is described. The reaction is catalyzed by copper, and the conditions proved to be mild and were amenable to a variety of functional groups. We expanded the Chan-Lam coupling to include C(sp³) nucleophiles and converted them into corresponding acetals. This method allows for the orthogonal acetalization of substrates with reactive, acid-sensitive functional groups.

High-Throughput Discovery and Evaluation of a General Catalytic Method for N-Arylation of Weakly Nucleophilic Sulfonamides

Through targeted high-throughput experimentation (HTE), we have identified the Pd/AdBippyPhos catalyst system as an effective and general method to construct densely functionalized N,N-diaryl sulfonamide motifs relevant to medicinal chemistry. AdBippyPhos is particularly effective for the installation of heteroaromatic groups. Computational steric parametrization of the investigated ligands reveals the potential importance of remote steric demand, where a large cone angle combined with an accessible Pd center is correlated to successful catalysts for C-N coupling reactions.

Modular Sulfondiimine Synthesis Using a Stable Sulfinylamine Reagent

Sulfondiimines—the double aza-analogues of sulfones—hold significant potential as leads in discovery chemistry, yet their application in this arena has been held back by the scarcity of appropriate synthetic routes. Existing methods employ sulfides as substrates, and rely on consecutive imination reactions using the hazardous reagent O-mesitylenesulfonyl hydroxylamine. Here we report a method for sulfondiimine synthesis that does not begin with a sulfide or a thiol, and instead employs two Grignard reagents and a bespoke sulfinylamine (R—N=S=O) reagent as starting materials. Lewis acid-mediated assembly of these three components provides efficient access to a series of sulfilimine intermediates. A novel rhodium-catalyzed imination of these electron-rich sulfilimines then delivers a varied range of sulfondiimines featuring orthogonal N-functionalization. Conditions for the selective manipulation of both N-atoms of the sulfondiimines are reported, allowing access to a broad range of mono- and difunctionalized products. The oxidation of the sulfilimine intermediates is also described, and provides a complementary route to sulfoximines.

Design of N-Benzoxaborole Benzofuran GSK8175-Optimization of Human Pharmacokinetics Inspired by Metabolites of a Failed Clinical HCV Inhibitor

We previously described the discovery of GSK5852 (1), a non-nucleoside polymerase (NS5B) inhibitor of hepatitis C virus (HCV), in which an N-benzyl boronic acid was essential for potent antiviral activity. Unfortunately, facile benzylic oxidation resulted in a short plasma half-life (5 h) in human volunteers, and a backup program was initiated to remove metabolic liabilities associated with 1. Herein, we describe second-generation NS5B inhibitors including GSK8175 (49), a sulfonamide-N-benzoxaborole analog with low in vivo clearance across preclinical species and broad-spectrum activity against HCV replicons. An X-ray structure of NS5B protein cocrystallized with 49 revealed unique protein-inhibitor interactions mediated by an extensive network of ordered water molecules and the first evidence of boronate complex formation within the binding pocket. In clinical studies, 49 displayed a 60–63 h half-life and a robust decrease in viral RNA levels in HCV-infected patients, thereby validating our hypothesis that reducing benzylic oxidation would improve human pharmacokinetics and lower efficacious doses relative to 1.

Chemoselective N-arylation of aminobenzene sulfonamides via copper catalysed Chan–Evans–Lam reactions

Chemoselective N-arylation of unprotected dinucleophilic aminobenzene sulfonamides was achieved via Cu-catalysed Chan–Evans–Lam cross-coupling with aryl boronic acids.

N,O-Bidentate ligand-tunable copper(ii) complexes as a catalyst for Chan-Lam coupling reactions of arylboronic acids with 1H-imidazole derivatives

An efficient procedure for Chan-Lam coupling reactions of arylboronic acids with 1H-imidazole derivatives using N,O-bidentate ligand-tunable copper(ii) complexes as a catalyst under base-free conditions has been developed. This protocol features mild reaction conditions, high yields and compatibility with different functional groups, providing a direct and facile strategy for the construction of C-N bonds and synthesis of heterocyclic compounds.

Convergent Synthesis of the NS5B Inhibitor GSK8175 Enabled by Transition Metal Catalysis

A convergent eight-stage synthesis of the boron-containing NS5B inhibitor GSK8175 is described. The previous route involves 13 steps in a completely linear sequence, with an overall 10% yield. Key issues include a multiday S_NAr arylation of a secondary sulfonamide using HMPA as solvent, multiple functional group interconversions after all of the carbon atoms are installed (including a Sandmeyer halogenation), use of carcinogenic chloromethyl methyl ether to install a protecting group late in the synthesis, and an unreliable Pd-catalyzed Miyaura borylation as the penultimate step. We have devised an orthogonal approach using a Chan-Lam coupling between a halogenated aryl pinacol boronate ester and an aryl methanesulfonamide. This reaction is performed using a cationic Cu(I) precatalyst, which can be easily generated in situ using KPF₆ as a halide abstractor. High-throughput screening revealed a new Pd catalyst system to effect the penultimate borylation chemistry using simple monodentate phosphine ligands, with PCyPh₂ identified as optimal. Reaction progress analysis of this borylation indicated likely mass-transfer rate limitations under standard conditions using KOAc as the base. We have devised a K₂CO₃/pivalic acid system as an alternative, which dramatically outperforms the standard conditions. This new synthesis proceeds in eight stages with a 20% overall yield.

Synthesis of Acridines from o-Aminoaryl Ketones and Arylboronic Acids by Copper Trifluoroacetate-Mediated Relay Reactions

An efficient and practical method for the synthesis of medicinally important acridines from readily available o-aminoaryl ketones and arylboronic acids was developed using copper(II)-mediated relay reactions that involve intermolecular Chan-Lam cross-coupling and subsequent intramolecular Friedel-Crafts-type reactions. A sole promoter, i.e., Cu(OTf)₂, was used; therefore, strongly acidic and basic conditions, nonreadily available or expensive substrates, additives, and noble-metal catalysts were not needed.