Copper-Catalyzed Functionalization of Benzylic C-H Bonds with N-Fluorobenzenesulfonimide: Switch from C-N to C-F Bond Formation Promoted by a Redox Buffer and Brønsted Base

Nitrogen-Based Organofluorine Functional Molecules: Synthesis and Applications

Fluorine and nitrogen form a successful partnership in organic synthesis, medicinal chemistry, and material sciences. Although fluorine-nitrogen chemistry has a long and rich history, this field has received increasing interest and made remarkable progress over the past two decades, driven by recent advancements in transition metal and organocatalysis and photochemistry. This review, emphasizing contributions from 2015 to 2023, aims to update the state of the art of the synthesis and applications of nitrogen-based organofluorine functional molecules in organic synthesis and medicinal chemistry. In dedicated sections, we first focus on fluorine-containing reagents organized according to the type of fluorine-containing groups attached to nitrogen, including N-F, N-RF, N-SRF, and N-ORF. This review also covers nitrogen-linked fluorine-containing building blocks, catalysts, pharmaceuticals, and agrochemicals, underlining these components' broad applicability and growing importance in modern chemistry.

Copper(I)-Initiated Site-Selective β-ζ-C(sp3)-H Bond Fluorination of Ketones, Carboxylic Esters, and Amides by Selectfluor

A synthetic method that enables the site-selective fluorination at an unactivated C(sp3)-H bond located two to six C-C bond distances from the C═O group in ketones, carboxylic esters, and amides by Selectfluor [1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate)] aided by a copper(I) salt is described. The site selectivity of the C(sp3)-F bond formation protocol was exemplified by the late-stage functionalization of five natural product and drug molecule derivatives.

Nonheme Mononuclear and Dinuclear Iron(II) and Iron(III) Fluoride Complexes and Their Fluorine Radical Transfer Reactivity

The nonheme iron(II) complexes containing a fluoride anion, FeII(BNPAPh2O)(F) (1) and [FeII(BNPAPh2OH)(F)(THF)](BF4) (2), were synthesized and structurally characterized. Addition of dioxygen to either 1 or 2 led to the formation of a fluoride-bridged, dinuclear iron(III) complex [Fe2III(BNPAPh2O)2(F)2(μ-F)]+ (4), which was characterized by single-crystal X-ray diffraction, 1H NMR, and elemental analysis. An iron(II)(iodide) complex, FeII(BNPAPh2O)(I) (3), was prepared and reacted with O2 to give the mononuclear complex cis-FeIII(BNPAPh2O)(OH)(I) (5). Addition of excess fluoride to 5 led to the formation of the oxo-bridged, dinuclear iron(III) complex [Fe2III(BNPAPh2O)2(F)2(μ-O)] (6), while the mononuclear iron(III)(fluoride) complex cis-FeIII(BNPAPh2O)(F)(Cl) (7) was prepared from the addition of excess F- to FeIII(BNPAPh2O)Cl2. The dinuclear complexes 4 and 6 were unreactive to fluorine radical transfer, but mononuclear 7 reacts with the radical substrate (p-MeO-C6H4)3C• to give the fluorine radical transfer products FeII(BNPAPh2O)(Cl) and (p-OMe-C6H4)3CF. These results show that a mononuclear FeIII(F) complex is capable of mediating fluorine radical transfer, even in the presence of second coordination sphere hydrogen bonds to the F- ligand. These findings are placed in context with what is known about the nonheme iron halogenases and related synthetic catalysts regarding their ability, or lack thereof, to mediate fluorine radical transfer reactions.

Electrophilic aromatic substitution of electron-rich arenes with N-fluorobenzenesulfonimide (NFSI) as an electrophile

An efficient amidation of electron-rich arenes using NFSI as a nitrogen source has been successfully disclosed. This amidation process can be easily conducted at elevated temperatures, without the need for catalysts or additives. A wide range of arenes substituted with hydroxy, alkoxy, or carbonyl groups were found to be compatible, yielding the desired amination products. Computational study shows that the amidation proceeds via an electrophilic aromatic substitution pathway, comprising a three-step process that includes substitution, addition, and elimination, which differs slightly from the classical mechanism.

Photoinduced Transition-Metal and External Photosensitizer Free Benzylic Fluorination of Unactivated Alkylarenes

A green and efficient protocol for the direct monofluorination of unactivated alkylarenes under visible-light irradiation has been developed, without any extraneous transition-metal catalysts or photosensitizers. This method is compatible with a broad spectrum of functional groups, including carboxylic and alcoholic scaffolds, under mild reaction conditions. Gram-scale synthesis of a fluorine-containing pharmaceutical analogue was successfully executed, underscoring the strategy's reliability and practicality. Furthermore, mechanistic studies suggest that a single-electron transfer mechanism might be responsible for the generation of the benzylic radicals in initiation step.

Recent Advances in Direct Regioselective C-H Chlorination at Aromatic and Aliphatic

Direct installation of key functionalities in a molecule through C-H bond activation is one of the thrust areas as well as challenging task in organic synthesis. Particularly, introduction of chlorine in a molecule imparts additional benefits for further functionalizations as well as improves the electronic behaviour such as lipophilicity and polarity towards drug development process. The chlorinated molecules have also been established as efficient biologically relevant scaffolds. Current manuscript has been focused on the direct installation of the chlorine atom at various aromatic and aliphatic positions to produce functional molecules. The key highlight of the manuscript belongs to the site selectivity (regioselectivity) for the installation of chlorine functionality. Manuscript describes the advanced methods developed for the direct C-H chlorination reactions and further simplified for the chlorination reactions at various positions including aromatic (o-, m-, and p-), benzylic, heteroaromatic, and aliphatic positions. Directing groups (DGs) and the coordination with the catalyst is the key for the enhancement of regioselectivities during direct C-H chlorination reactions.

Mechanistic insights into radical formation and functionalization in copper/N-fluorobenzenesulfonimide radical-relay reactions

Copper-catalysed radical-relay reactions that employ N-fluorobenzenesulfonimide (NFSI) as the oxidant have emerged as highly effective methods for C(sp3)-H functionalization. Herein, computational studies are paired with experimental data to investigate a series of key mechanistic features of these reactions, with a focus on issues related to site-selectivity, enantioselectivity, and C-H substrate scope. (1) The full reaction energetics of enantioselective benzylic C-H cyanation are probed, and an adduct between Cu and the N-sulfonimidyl radical (˙NSI) is implicated as the species that promotes hydrogen-atom transfer (HAT) from the C-H substrate. (2) Benzylic versus 3° C-H site-selectivity is compared with different HAT reagents: Cu/˙NSI, ˙OtBu, and Cl˙, and the data provide insights into the high selectivity for benzylic C-H bonds in Cu/NFSI-catalyzed C-H functionalization reactions. (3) The energetics of three radical functionalization pathways are compared, including radical-polar crossover (RPC) to generate a carbocation intermediate, reductive elimination from a formal CuIII organometallic complex, and radical addition to a Cu-bound ligand. The preferred mechanism is shown to depend on the ligands bound to copper. (4) Finally, the energetics of three different pathways that convert benzylic C-H bonds into benzylic cations are compared, including HAT/ET (ET = electron transfer), relevant to the RPC mechanism with Cu/NFSI; hydride transfer, involved in reactions with high-potential quinones; and sequential ET/PT/ET (PT = proton transfer), involved in catalytic photoredox reactions. Collectively, the results provide mechanistic insights that establish a foundation for further advances in radical-relay C-H functionalization reactions.

Copper-Catalyzed Benzylic C-H Cross-Coupling Enabled by Redox Buffers: Expanding Synthetic Access to Three-Dimensional Chemical Space

ConspectusCross-coupling methods are the most widely used synthetic methods in medicinal chemistry. Existing reactions are dominated by methods such as amide coupling and arylation reactions that form bonds to sp2-hybridized carbon atoms and contribute to the formation of "flat" molecules. Evidence that three-dimensional structures often have improved physicochemical properties for pharmaceutical applications has contributed to growing demand for cross-coupling methods with sp3-hybridized reaction partners. Substituents attached to sp3 carbon atoms are intrinsically displayed in three dimensions. These considerations have led to efforts to establish reactions with sp3 cross-coupling partners, including alkyl halides, amines, alcohols, and carboxylic acids. As C(sp3)-H bonds are much more abundant that these more conventional coupling partners, we have been pursuing C(sp3)-H cross-coupling reactions that achieve site-selectivity, synthetic utility, and scope competitive with conventional coupling reactions.In this Account, we outline Cu-catalyzed oxidative cross-coupling reactions of benzylic C(sp3)-H bonds with diverse nucleophilic partners. These reactions commonly use N-fluorobenzenesulfonimide (NFSI) as the oxidant. The scope of reactivity is greatly improved by using a "redox buffer" that ensures that the Cu catalyst is available in the proper redox state to promote the reaction. Early precedents of catalytic Cu/NFSI oxidative coupling reactions, including C-H cyanation and arylation, did not require a redox buffer, but reactions with other nucleophiles, such as alcohols and azoles, were much less effective under similar conditions. Mechanistic studies show that some nucleophiles, such as cyanide and arylboronic acids, promote in situ reduction of CuII to CuI, contributing to successful catalytic turnover. Poor reactivity was observed with nucleophiles, such as alcohols, that do not promote CuII reduction in the same manner. This insight led to the identification of sacrificial reductants, termed "redox buffers", that support controlled generation of CuI during the reactions and enable successful benzylic C(sp3)-H cross-coupling with diverse nucleophiles. Successful reactions include those that feature direct coupling of (hetero)benzylic C-H substrates with coupling partners (alcohols, azoles) and sequential C(sp3)-H functionalization/coupling reactions. The latter methods feature generation of a synthetic linchpin that can undergo subsequent reaction with a broad array of nucleophiles. For example, halogenation/substitution cascades afford benzylic amines, (thio)ethers, and heterodiarylmethane derivatives, and an isocyanation/amine-addition sequence generates diverse benzylic ureas.Collectively, these Cu-catalyzed (hetero)benzylic C(sp3)-H cross-coupling reactions rapidly access diverse molecules. Analysis of their physicochemical and topological properties highlights the "drug-likeness" and enhanced three-dimensionality of these products relative to existing bioactive molecules. This consideration, together with the high benzylic C-H site-selectivity and the broad scope of reactivity enabled by the redox buffering strategy, makes these C(sp3)-H cross-coupling methods ideally suited for implementation in high-throughput experimentation platforms to explore novel chemical space for drug discovery and related applications.

Accessing three-dimensional molecular diversity through benzylic C-H cross-coupling

Pharmaceutical and agrochemical discovery efforts rely on robust methods for chemical synthesis that rapidly access diverse molecules1,2. Cross-coupling reactions are the most widely used synthetic methods3, but these methods typically form bonds to C(sp2)-hybridized carbon atoms (e.g., amide coupling, biaryl coupling) and lead to a prevalence of "flat" molecular structures with suboptimal physicochemical and topological properties4. Benzylic C(sp3)-H cross-coupling methods offer an appealing strategy to address this limitation by directly forming bonds to C(sp3)-hybridized carbon atoms, and emerging methods exhibit synthetic versatility that rivals conventional cross-coupling methods to access products with drug-like properties. Here, we use a virtual library of >350,000 benzylic ethers and ureas derived from benzylic C-H cross-coupling to test the widely held view that coupling at C(sp3)-hybridized carbon atoms affords products with improved three-dimensionality. The results show that the conformational rigidity of the benzylic scaffold strongly influences the product dimensionality. Products derived from flexible scaffolds often exhibit little or no improvement in three-dimensionality, unless they adopt higher energy conformations. This outcome introduces an important consideration when designing routes to topologically diverse molecular libraries. The concepts elaborated herein are validated experimentally through an informatics-guided synthesis of selected targets and the use of high-throughput experimentation to prepare a library of three-dimensional products that are broadly distributed across drug-like chemical space.

Oxidative Cross Dehydrogenative Coupling of N-Heterocycles with Aldehydes through C(sp3)-H Functionalization

Existing methodologies for metal-catalyzed cross-couplings typically rely on preinstallation of reactive functional groups on both reaction partners. In contrast, C-H functionalization approaches offer promise in simplification of the requisite substrates; however, challenges from low reactivity and similar reactivity of various C-H bonds introduce considerable complexity. Herein, the oxidative cross dehydrogenative coupling of α-amino C(sp3)-H bonds and aldehydes to produce ketone derivatives is described using an unusual reaction medium that incorporates the simultaneous use of di-tert-butyl peroxide as an oxidant and zinc metal as a reductant. The method proceeds with a broad substrate scope, representing an attractive approach for accessing α-amino ketones through the formal acylation of C-H bonds α to nitrogen in N-heterocycles. A combination of experimental investigation and computational modeling provides evidence for a mechanistic pathway involving cross-selective nickel-mediated cross-coupling of α-amino radicals and acyl radicals.

Benzylic C-H Esterification with Limiting C-H Substrate Enabled by Photochemical Redox Buffering of the Cu Catalyst

Copper-catalyzed radical-relay reactions provide a versatile strategy for selective C-H functionalization; however, reactions with peroxide-based oxidants often require excess C-H substrate. Here, we report a photochemical strategy to overcome this limitation by using a Cu/2,2'-biquinoline catalyst that supports benzylic C-H esterification with limiting C-H substrate. Mechanistic studies indicate that blue-light irradiation promotes carboxylate-to-copper charge transfer, reducing resting-state CuII to CuI, which activates the peroxide to generate an alkoxyl radical hydrogen-atom-transfer species. This "photochemical redox buffering" introduces a unique strategy to sustain the activity of Cu catalysts in radical-relay reactions.

Copper-Catalyzed Intermolecular Cross-dehydrogenative C-N Coupling at Room Temperature via Remote Activating Group Enabled Radical Relay Strategy

Employing N-fluorobenzenesulfonimide (NFSI) as a nitrogen-centered radical (NCR) precursor, an intermolecular C(sp²)-N coupling on heteroarenes or substituted benzenes with remote activated aniline derivatives via copper catalyzed N-N radical relay strategy at room temperature is developed. Good to excellent yields are acquired, and no ligand or additive is required. Reaction scope investigation and preliminary mechanistic studies demonstrate that the remote activating strategy and delicate control on the reactivities of active NCR species are essential to guarantee satisfactory chemo- and site-selectivity.

Catalytic System for Aerobic Oxidation That Simultaneously Functions as Its Own Redox Buffer

The control of the solution electrochemical potential as well as pH impacts products in redox reactions, but the former gets far less attention. Redox buffers facilitate the maintenance of potentials and have been noted in diverse cases, but they have not been a component of catalytic systems. We report a catalytic system that contains its own built-in redox buffer. Two highly synergistic components (a) the tetrabutylammonium salt of hexavanadopolymolybdate TBA₄H₅[PMo₆V₆O₄₀] (PV₆Mo₆) and (b) Cu(ClO₄)₂ in acetonitrile catalyze the aerobic oxidative deodorization of thiols by conversion to the corresponding nonodorous disulfides at 23 °C (each catalyst alone is far less active). For example, the reaction of 2-mercaptoethanol with ambient air gives a turnover number (TON) = 3 × 10² in less than one hour with a turnover frequency (TOF) of 6 × 10^-2 s^-1 with respect to PV₆Mo₆. Multiple electrochemical, spectroscopic, and other methods establish that (1) PV₆Mo₆, a multistep and multielectron redox buffering catalyst, controls the speciation and the ratio of Cu(II)/Cu(I) complexes and thus keeps the solution potential in different narrow ranges by involving multiple POM redox couples and simultaneously functions as an oxidation catalyst that receives electrons from the substrate; (2) Cu catalyzes two processes simultaneously, oxidation of the RSH by PV₆Mo₆ and reoxidation of reduced PV₆Mo₆ by O₂; and (3) the analogous polytungstate-based system, TBA₄H₅[PW₆V₆O₄₀] (PV₆W₆), has nearly identical cyclic voltammograms (CV) as PV₆Mo₆ but has almost no catalytic activity: it does not exhibit self-redox buffering.

Copper-Catalyzed Electrochemical C-H Fluorination

We report the systematic development of an electrooxidative methodology that translates stoichiometric C-H fluorination reactivity of an isolable CuIII fluoride complex into a catalytic process. The critical challenges of electrocatalysis with a highly reactive CuIII species were addressed by the judicious selection of electrolyte, F- source, and sacrificial electron acceptor. Catalyst-controlled C-H fluorination occurs with a preference for hydridic C-H bonds with high bond dissociation energies over weaker but less hydridic C-H bonds. The selectivity is driven by an oxidative asynchronous proton-coupled elelctron transfer (PCET) at an electrophilic CuIII-F complex. We further demonstrate that the asynchronicity factor of hydrogen atom transfer η can be used as a guideline to rationalize the selectivity of C-H fluorination.

Visible-light-initiated external photocatalyst-free synthesis of α,α-difluoro-β-ketoamides from 4-aminocoumarins

A concise and efficient ring-opening difluorination strategy was developed for the synthesis of highly functionalized hydroxy-containing α,α-difluoro-β-ketoamides from the one-pot multicomponent reaction of 4-aminocoumarins, NFSI, and water in dimethyl carbonate (DMC) as a green solvent. The reactions were smoothly achieved under visible light irradiation in air at room temperature without the addition of any other external photocatalysts. With this protocol, various α,α-difluoro-β-ketoamides were successfully synthesized under mild conditions (25 examples, 73-91% yields). This transition-metal-free synthetic procedure shows good functional group compatibility and attractive practical potential for large-scale synthesis.

Direct Benzylic C(sp3)-O Coupling with Alcohol via Site-Selective C(sp3)-H Cleavage at Room Temperature through a Remote Directing Group-Enabled Radical Relay Strategy

Employing a low loading of the terminal oxidant, a remote directing group-enabled radical relay strategy for benzylic direct C(sp³)-H alkoxylation with alcohols at room temperature is developed. Satisfactory site-selectivity, chemoselectivity, and reaction scope are achieved under simple and mild conditions, and no ligand or additive is required. Mechanistic studies, ready conversions of the directing group, and other benzylic functionalizations currently under development in our laboratory further indicate the promising potentials of this remote directing group-enabled radical relay strategy.

Copper-catalyzed radical cascade reaction of simple cyclobutanes: synthesis of highly functionalized cyclobutene derivatives

Cyclobutenes as versatile and highly valuable synthons have been widely applied in synthesis. Although various methods for their synthesis have been well established, new strategies for the construction of the cyclobutene skeleton from simple substrates are still highly desirable. Starting from simple cyclobutanes, the construction of the cyclobutene skeleton especially introducing multiple functional groups simultaneously had never been achieved. Here, we developed a novel radical cascade strategy for the synthesis of highly functionalized cyclobutenes directly from cyclobutanes involving rare cleavage of four or five C–H bonds and formation of two C–N/C–S or three C–Br bonds. With copper as catalyst and N-fluorobenzenesulfonimide (NFSI) as oxidant, a wide range of diaminated, disulfonylated and tribrominated cyclobutene derivatives were efficiently synthesized.

A novel radical cascade strategy for the synthesis of highly functionalized cyclobutenes directly from cyclobutanes involving rare four or five C–H bonds cleavage and two C–N/C–S or three C–Br bonds formation has been successfully developed.

Radical C(sp3)-H functionalization and cross-coupling reactions

C─H functionalization reactions are playing an increasing role in the preparation and modification of complex organic molecules, including pharmaceuticals, agrochemicals, and polymer precursors. Radical C─H functionalization reactions, initiated by hydrogen-atom transfer (HAT) and proceeding via open-shell radical intermediates, have been expanding rapidly in recent years. These methods introduce strategic opportunities to functionalize C(sp3)─H bonds. Examples include synthetically useful advances in radical-chain reactivity and biomimetic radical-rebound reactions. A growing number of reactions, however, proceed via "radical relay" whereby HAT generates a diffusible radical that is functionalized by a separate reagent or catalyst. The latter methods provide the basis for versatile C─H cross-coupling methods with diverse partners. In the present review, highlights of recent radical-chain and radical-rebound methods provide context for a survey of emerging radical-relay methods, which greatly expand the scope and utility of intermolecular C(sp3)─H functionalization and cross coupling.

An N-Fluorinated Imide for Practical Catalytic Imidations

Catalytic imidation using NFSI as the nitrogen source has become an emerging tool for oxidative carbon-nitrogen bond formation. However, the less than ideal benzenesulfonimide moiety is incorporated into products, severely detracting its synthetic value. As a solution to this challenge, we report herein the development of a novel N-fluorinated imide, N-fluoro-N-(fluorosulfonyl)carbamate (NFC), by which the attached imide moiety acts as a modular synthetic handle for one-step derivatization to amines, sulfonamides, and sulfamides. Furthermore, this study revealed the superior reactivity of NFC as showcased in a copper-catalyzed imidation of benzene derivatives and imidocyanation of aliphatic alkenes, overcoming the limitation of NFSI-mediated reactions.

Cu-Catalyzed Site-Selective Benzylic Chlorination Enabling Net C-H Coupling with Oxidatively Sensitive Nucleophiles

Site-selective chlorination of benzylic C-H bonds is achieved using a CuICl/bis(oxazoline) catalyst with N-fluorobenzenesulfonimide as the oxidant and KCl as a chloride source. This method exhibits higher benzylic selectivity, relative to established chlorination protocols, and is compatible with diverse alkyl arenes. Sequential benzylic C-H chlorination/nucleophilic substitution affords C-O, C-S, and C-N coupling products with oxidatively sensitive coupling partners.

Remote carbamate-directed site-selective benzylic C–H oxygenation via synergistic copper/TEMPO catalysis at room temperature

A benzylic C(sp3)–H oxygenation with water at room temperature through a ligand- and additive-free synergistic copper/TEMPO-catalysed radical relay pathway and a remote directing strategy is described.

Construction of Carbon-Fluorine Bonds via Copper-Catalyzed/-Mediated Fluorination Reactions

The construction of carbon-fluorine bonds is an important yet challenging task in organic synthesis. Transition metal-catalyzed/-mediated C-F bond forming processes have recently emerged as a viable strategy and provided access to value-added monofluorinated compounds. A dramatic increase in fluorination methods using inexpensive and earth-abundant copper can be seen in the past decade surpassing those using palladium and silver. This review discusses the recent development of Cu-catalyzed/-mediated formation of C(sp² )-F and C(sp³ )-F bonds.

(1-Selenocyanatoethyl)benzene: A Selenocyanation Reagent for Site-Selective Selenocyanation of Inert Alkyl C(sp3)-H Bonds

A new, simple, yet easily accessible, (1-selenocyanatoethyl)benzene has been designed and applied as a SeCN group transfer reagent for selenocyanation of aliphatic C(sp³)-H bonds for the first time. This protocol is featured with mild reaction conditions and wide substrate scope. Control experiments reveal that a radical-group transfer mechanism might be involved.

Copper-Catalyzed Cross-Coupling of Benzylic C-H Bonds and Azoles with Controlled N-Site Selectivity

Azoles are important motifs in medicinal chemistry, and elaboration of their structures via direct N-H/C-H coupling could have broad utility in drug discovery. The ambident reactivity of many azoles, however, presents significant selectivity challenges. Here, we report a copper-catalyzed method that achieves site-selective cross-coupling of pyrazoles and other N-H heterocycles with substrates bearing (hetero)benzylic C-H bonds. Excellent N-site selectivity is achieved, with the preferred site controlled by the identity of co-catalytic additives. This cross-coupling strategy features broad scope for both the N-H heterocycle and benzylic C-H coupling partners, enabling application of this method to complex molecule synthesis and medicinal chemistry.

Copper catalyzed late-stage C(sp3)-H functionalization of nitrogen heterocycles

Nitrogen heterocycle represents a ubiquitous skeleton in natural products and drugs. Late-stage C(sp3)-H bond functionalization of N-heterocycles with broad substrate scope remains a challenge and of particular significance to modern chemical synthesis and pharmaceutical chemistry. Here, we demonstrate copper-catalysed late-stage C(sp3)-H functionalizaion of N-heterocycles using commercially available catalysts under mild reaction conditions. We have investigated 8 types of N-heterocycles which are usually found as medicinally important skeletons. The scope and utility of this approach are demonstrated by late-stage C(sp3)-H modification of these heterocycles including a number of pharmaceuticals with a broad range of nucleophiles, e.g. methylation, arylation, azidination, mono-deuteration and glycoconjugation etc. Preliminary mechanistic studies reveal that the reaction undergoes a C-H fluorination process which is followed by a nucleophilic substitution.

Benzylic C-H isocyanation/amine coupling sequence enabling high-throughput synthesis of pharmaceutically relevant ureas

C(sp³)–H functionalization methods provide an ideal synthetic platform for medicinal chemistry; however, such methods are often constrained by practical limitations. The present study outlines a C(sp³)–H isocyanation protocol that enables the synthesis of diverse, pharmaceutically relevant benzylic ureas in high-throughput format. The operationally simple C–H isocyanation method shows high site selectivity and good functional group tolerance, and uses commercially available catalyst components and reagents [CuOAc, 2,2′-bis(oxazoline) ligand, (trimethylsilyl)isocyanate, and N-fluorobenzenesulfonimide]. The isocyanate products may be used without isolation or purification in a subsequent coupling step with primary and secondary amines to afford hundreds of diverse ureas. These results provide a template for implementation of C–H functionalization/cross-coupling in drug discovery.

A copper-based catalyst system composed of commercially available reagents enables C–H isocyanation with exquisite (hetero)benzylic site selectivity, enabling high-throughput access to pharmaceutically relevant ureas via coupling with amines.

Alkali Metal Fluorides in Fluorinated Alcohols: Fundamental Properties and Applications to Electrochemical Fluorination

Fundamental properties of alkali metal fluorides (MF, M = Cs, K) dissolved in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) or in 3,3,3-trifluoroethanol (TFE) are investigated, including solubility, conductivity, and viscosity. Solid-state structures of single crystals obtained from CsF/HFIP and CsF/TFE are described for the first time, giving insights into the multiple interactions between fluorinated alcohols and CsF. Applications in electrochemical fluorination reactions are successfully demonstrated.

β-Selective Cu(II)-Catalyzed Dehydrogenative Enamination of Alkylbenzenes

A Cu(II)-catalyzed dehydrogenative enamination that couples alkyl-substituted electron-rich arenes and N-fluorobenzenesulfonimide to forge enamine products is reported. This C-N bond-forming procedure occurs selectively at the β-position of the alkyl group. Both aniline and anisole derivatives are tolerated under these conditions, to afford styryl amines. A reaction mechanism involving quinone methide and styrene intermediates is proposed.

Copper-Catalyzed C-H Fluorination/Functionalization Sequence Enabling Benzylic C-H Cross Coupling with Diverse Nucleophiles

Site-selective transformation of benzylic C-H bonds into diverse functional groups is achieved via Cu-catalyzed C-H fluorination with N-fluorobenzenesulfonimide (NFSI), followed by substitution of the resulting fluoride with various nucleophiles. The benzyl fluorides generated in these reactions are reactive electrophiles in the presence of hydrogen-bond donors or Lewis acids, allowing them to be used without isolation in C-O, C-N, and C-C coupling reactions.

Copper-catalyzed oxidative benzylic C(sp3)–H amination: direct synthesis of benzylic carbamates

A Cu(i)–diimine ligand combined with a N–F source allows the C–H abstraction and incorporation of a carbamate functional group in the hydrocarbons at the benzylic position.