Synthesis and late-stage functionalization of complex molecules through C-H fluorination and nucleophilic aromatic substitution

Radical meta-C-H Halogenation of Azines via N-Benzyl Activation Strategy

Regioselective halogenation of six-membered N-heteroarenes is crucial for precise functional derivatization. We present a meta-selective halogenation method for pyridines, quinolines, and isoquinolines via electrophilic halogen radical addition utilizing an N-benzyl activation strategy. This method achieves C3- and C5-dihalogenation in pyridines, C3- and C6-dihalogenation in quinolines, and C3-monohalogenation in isoquinolines. The feasibility and potential applications of this method were validated through scale-up reactions and the bromination of quinoline derivatives with biomolecular fragments.

Direct C-H Hydroxylation of N-Heteroarenes and Benzenes via Base-Catalyzed Halogen Transfer

Hydroxylated (hetero)arenes are valued in many industries as both key constituents of end products and diversifiable synthetic building blocks. Accordingly, the development of reactions that complement and address the limitations of existing methods for the introduction of aromatic hydroxyl groups is an important goal. To this end, we apply base-catalyzed halogen transfer (X-transfer) to enable the direct C-H hydroxylation of mildly acidic N-heteroarenes and benzenes. This protocol employs an alkoxide base to catalyze X-transfer from sacrificial 2-halothiophene oxidants to aryl substrates, forming SNAr-active intermediates that undergo nucleophilic hydroxylation. Key to this process is the use of 2-phenylethanol as an inexpensive hydroxide surrogate that, after aromatic substitution and rapid elimination, provides the hydroxylated arene and styrene byproduct. Use of simple 2-halothiophenes allows for C-H hydroxylation of 6-membered N-heteroarenes and 1,3-azole derivatives, while a rationally designed 2-halobenzothiophene oxidant extends the scope to electron-deficient benzene substrates. Mechanistic studies indicate that aromatic X-transfer is reversible, suggesting that the deprotonation, halogenation, and substitution steps operate in synergy, manifesting in unique selectivity trends that are not necessarily dependent on the most acidic aryl position. The utility of this method is further demonstrated through streamlined target molecule syntheses, examples of regioselectivity that contrast alternative C-H hydroxylation methods, and the scalable recycling of the thiophene oxidants.

Late-stage modification of bioactive compounds: Improving druggability through efficient molecular editing

Synthetic chemistry plays an indispensable role in drug discovery, contributing to hit compounds identification, lead compounds optimization, candidate drugs preparation, and so on. As Nobel Prize laureate James Black emphasized, "the most fruitful basis for the discovery of a new drug is to start with an old drug"1. Late-stage modification or functionalization of drugs, natural products and bioactive compounds have garnered significant interest due to its ability to introduce diverse elements into bioactive compounds promptly. Such modifications alter the chemical space and physiochemical properties of these compounds, ultimately influencing their potency and druggability. To enrich a toolbox of chemical modification methods for drug discovery, this review focuses on the incorporation of halogen, oxygen, and nitrogen-the ubiquitous elements in pharmacophore components of the marketed drugs-through late-stage modification in recent two decades, and discusses the state and challenges faced in these fields. We also emphasize that increasing cooperation between chemists and pharmacists may be conducive to the rapid discovery of new activities of the functionalized molecules. Ultimately, we hope this review would serve as a valuable resource, facilitating the application of late-stage modification in the construction of novel molecules and inspiring innovative concepts for designing and building new drugs.

Oxidative Nickel-Catalyzed ortho-C-H Amination of (Iso)quinolines with Alicyclic Amines Directed by a Sacrificial N-Oxide Group

Transition metal (TM)-catalyzed direct amination of C-H bonds on free or fused pyridine (Py) rings with free amines still remains scarce because amines and the Py ring tend to adopt a nonproductive N-bound coordination with many TMs, leading to a significant decrease of catalytic reactivity. We herein disclose a nickel-catalyzed and a sacrificial N-oxide group directed oxidative coupling of (iso)quinolyl C-H bonds and alicyclic amines, which furnishes bioimportant amino(iso)quinolines efficiently and selectively in a single step. Noteworthy, this protocol avoids the use of aggressive reactants and very strong bases usually required when aminating on nonoxidized Py rings.

Data Driven Computational Design and Experimental Validation of Drugs for Accelerated Mitigation of Pandemic-like Scenarios

Emerging pathogens are a historic threat to public health and economic stability. Current trial-and-error approaches to identify new therapeutics are often ineffective due to their inefficient exploration of the enormous small molecule design space. Here, we present a data-driven computational framework composed of hybrid evolutionary algorithms for evolving functional groups on existing drugs to improve their binding affinity toward the main protease (Mpro) of SARS-CoV-2. We show that combinations of functional groups and sites are critical to design drugs with improved binding affinity, which can be easily achieved using our framework by exploring a fraction of the available search space. Atomistic simulations and experimental validation elucidate that enhanced and prolonged interactions between functionalized drugs and Mpro residues result in their improved therapeutic value over that of the parental compound. Overall, this novel framework is extremely flexible and has the potential to rapidly design inhibitors for any protein with available crystal structures.

Straightforward Synthesis of Halopyridine Aldehydes via Diaminomethylation

A novel two-step method for formylation of fluoropyridines with silylformamidine Me3 SiC(=NMe)NMe2 (1) under catalyst-free conditions was developed. A series of all possible 18 fluoropyridines featuring one to four fluorine atoms were subjected to the reaction with 1 existing in equilibrium with its carbenic form Me2 NC(:)N(Me)SiMe3 (1'). Among them, 12 fluoropyridines were shown to react via C-H insertion. The reaction proceeded either at β- or γ-positions affording the corresponding aminals. The more fluorine atoms in pyridines, the easier the reaction proceeded. We also hypothesized that the pyridines in which the fluorine was substituted by other halogens would react in a similar manner. To test the hypothesis, a set of 3,5-disubstituted pyridines with various combination of halogen atoms was prepared. 3,5-Difluoropyridine was taken as a compound for comparison. All the pyridines in the series also reacted likewise. In most cases, hydrolysis of the aminals afforded the corresponding aldehydes. As DFT calculations indicate, the reaction mechanism includes deprotonation of pyridine by 1' as a strong base and the following rearrangement of the formed tight ionic pair to the final product. An alternative reaction pathway involving addition of 1' to the pyridine carbon with the following hydrogen transfer via a three-membered transition state structure required much higher activation energy.

C-H Bond Functionalization of N-Heteroarenes Mediated by Selectfluor

Herein, recent developments for Selectfluor-mediated C-H functionalization of N-heteroarenes are described. This type of C-H bond activation is an attractive and competitive alternative to traditional methodologies, allowing the functionalization of a variety of chemical functions. In addition, Selectfluor is a more sustainable and economically accessible oxidant compared with expensive/toxic metals or hazardous peroxides. For a practical understanding, the current review classified systematically the reported strategies in four subsections as follows: (1) carbon-carbon formation, (2) carbon-nitrogen bond formation, (3) carbon-chalcogen bond, and (4) carbon-halogen bond formation. Mechanistic aspects and reaction conditions are fully discussed to provide an understanding of the aspects that govern C-H functionalization in N-heteroarenes mediated by Selectfluor.

Electron-Transfer-Enabled Concerted Nucleophilic Fluorination of Azaarenes: Selective C-H Fluorination of Quinolines

Direct C-H fluorination is an efficient strategy to construct aromatic C-F bonds, but the cleavage of specific C-H bonds in the presence of other functional groups and the high barrier of C-F bond formation make the transformation challenging. Progress for the electrophilic fluorination of arenes has been reported, but a similar transformation for electron-deficient azaarenes has remained elusive due to the high energy of the corresponding Wheland intermediates. Nucleophilic fluorination of electron-deficient azaarenes is difficult owing to the identity of the Meisenheimer intermediate after fluoride attack, from which fluoride elimination to regenerate the substrate is favored over hydride elimination to form the product. Herein, we report a new concept for C-H nucleophilic fluorination without the formation of azaarene Meisenheimer intermediates through a chain process with an asynchronous concerted F--e--H+ transfer. The concerted nucleophilic aromatic substitution strategy allows for the first successful nucleophilic oxidative fluorination of quinolines.

Cross-Coupling Reactions Enabled by Well-Defined Ag(III) Compounds: Main Focus on Aromatic Fluorination and Trifluoromethylation

AgIII compounds are considered strong oxidizers of difficult handling. Accordingly, the involvement of Ag catalysts in cross-coupling via 2e- redox sequences is frequently discarded. Nevertheless, organosilver(III) compounds have been authenticated using tetradentate macrocycles or perfluorinated groups as supporting ligands, and since 2014, first examples of cross-coupling enabled by AgI /AgIII redox cycles saw light. This review collects the most relevant contributions to this field, with main focus on aromatic fluorination/perfluoroalkylation and the identification of AgIII key intermediates. Pertinent comparison between the activity of AgIII RF compounds in aryl-F and aryl-CF3 couplings vs. the one shown by its CuIII RF and AuIII RF congeners is herein disclosed, thus providing a more profound picture on the scope of these transformations and the pathways commonly associated to C-RF bond formations enabled by coinage metals.

Iron-Catalyzed Intermolecular C-N Cross-Coupling Reactions via Radical Activation Mechanism

A concept for intermolecular C-N cross-coupling amination has been discovered using tetrazoles and aromatic and aliphatic azides with boronic acids under iron-catalyzed conditions. The amination follows an unprecedented metalloradical activation mechanism that is different from traditional metal-catalyzed C-N cross-coupling reactions. The scope of the reaction has been demonstrated by the employment of a large number of tetrazoles, azides, and boronic acids. Moreover, several late-stage aminations and a short synthesis of a drug candidate have been showcased for further synthetic utility. Collectively, this iron-catalyzed C-N cross-coupling should have wide applications in the context of medicinal chemistry, drug discovery, and pharmaceutical industries.

Late-Stage C-H Functionalization of Azines

Azines, such as pyridines, quinolines, pyrimidines, and pyridazines, are widespread components of pharmaceuticals. Their occurrence derives from a suite of physiochemical properties that match key criteria in drug design and is tunable by varying their substituents. Developments in synthetic chemistry, therefore, directly impact these efforts, and methods that can install various groups from azine C-H bonds are particularly valuable. Furthermore, there is a growing interest in late-stage functionalization (LSF) reactions that focus on advanced candidate compounds that are often complex structures with multiple heterocycles, functional groups, and reactive sites. Because of factors such as their electron-deficient nature and the effects of the Lewis basic N atom, azine C-H functionalization reactions are often distinct from their arene counterparts, and the application of these reactions in LSF contexts is difficult. However, there have been many significant advances in azine LSF reactions, and this review will describe this progress, much of which has occurred over the past decade. It is possible to categorize these reactions as radical addition processes, metal-catalyzed C-H activation reactions, and transformations occurring via dearomatized intermediates. Substantial variation in reaction design within each category indicates both the rich reactivity of these heterocycles and the creativity of the approaches involved.

Analogy of the Reactions of Aromatic and Aliphatic π-Electrophiles with Nucleophiles

The aim of this essay is to disclose the similarity of a great variety of reactions that proceed between nucleophiles and π-electrophiles-both aromatic and aliphatic. These reactions proceed via initial reversible addition, followed by a variety of transformations that are common for the adducts of both aliphatic and aromatic electrophiles. We hope that understanding of this analogy should help to expand the scope of the known reactions and inspire the search for new reactions that were overlooked.

C3-Cyanation of Pyridines: Constraints on Electrophiles and Determinants of Regioselectivity

Methods for C-H cyanation of pyridines are rare. Here, we report a method for C3-selective cyanation of pyridines by a tandem process with the reaction of an in situ generated dihydropyridine with a cyano electrophile as the key step. The method is suitable for late-stage functionalization of pyridine drugs. The low reduction potential of the electrophile and effective transfer of the nitrile group were found to be essential for the success of this method. We studied the reaction mechanism in detail by means of control experiments and theoretical calculations and found that a combination of electronic and steric factors determined the regioselectivity of reactions involving C2-substituted pyridines.

Palladium-Catalyzed Cyanation of Arenediazonium Tetrafluoroborate Derivatives with 2-(Piperidin-1-yl)acetonitrile as the Cyano Source

The present study describes the one-pot palladium-catalyzed cyanation of commercially available aryldiazonium tetrafluoroborate derivatives with 2-(piperidin-1-yl)acetonitrile (an organic cyano reagent) under mild conditions. This process utilizes a Pd/(Me3Si)2 system and is applied to a wide scope of aromatic diazonium substrates to give the corresponding nitrile-containing products in moderate to high yields (59–92%). This methodology is employed for the preparation of etravirine, a drug used for the treatment of HIV, and for transformations of 1H-indole-2-carbonitrile into compounds that are used as a NMDA receptor antagonists and that have high potential against mutant HIV strains. The mechanism proposed for this Pd-catalyzed cyanation involves cyanide ions, as confirmed using indicator paper.

C2-Selective, Functional-Group-Divergent Amination of Pyrimidines by Enthalpy-Controlled Nucleophilic Functionalization

Synthesis of heteroaryl amines has been an important topic in organic chemistry because of their importance in small-molecule discovery. In particular, 2-aminopyrimidines represent a highly privileged structural motif that is prevalent in bioactive molecules, but a general strategy to introduce the pyrimidine C2-N bonds via direct functionalization is elusive. Here we describe a synthetic platform for site-selective C-H functionalization that affords pyrimidinyl iminium salt intermediates, which then can be transformed into various amine products in situ. Mechanism-based reagent design allowed for the C2-selective amination of pyrimidines, opening the new scope of site-selective heteroaryl C-H functionalization. Our method is compatible with a broad range of pyrimidines with sensitive functional groups and can access complex aminopyrimidines with high selectivity.

Cu/base co-catalyzed [3+3] cycloaddition for the synthesis of highly functionalized 4-fluoropyridines

An efficient, straightforward and general method for the de novo synthesis of highly functionalized 4-fluoropyridines was developed via a cooperative copper- and base-catalyzed [3+3] cycloaddition of active methylene isocyanides with difluorocyclopropenes. The resulting 4-fluoropyridines can be readily diversified by various nucleophiles.

A late-stage diversification via Heck-Matsuda arylation: Straightforward synthesis and cytotoxic/antiproliferative profiling of novel aryl-labdane-type derivatives

In the current study a late-stage diversification of unactivated olefins labd-8(17)-en-15-oic acid (1a) and methyl labd-8(17)-en-15-oate (1b) via Heck-Matsuda arylation is described. The reaction provided straightforward and practical access to a series of novel aryl-labdane-type derivatives (HM adducts 3a-h) in moderate to good yields in a highly regio- and stereoselective manner at room temperature under air atmosphere. The cytotoxic activity of these compounds was investigated in vitro against three different human cell lines (THP-1, K562, MCF-7). Of these, HM adduct 3h showed a selective effect in all cancer cell lines tested and was selected for extended biological investigations in a leukemia cell line (K562), which demonstrated that the cytotoxic/antiproliferative activity observed in this compound might be mediated by induction of cell cycle arrest at the sub-G1 phase and by autophagy-induced cell death. Taken together, these findings indicate that further investigation into the anticancer activity against chronic myeloid leukemia from aryl-labdane-type derivatives may be fruitful.

An overview of the synthetic route to the marketed formulations of pyrimidine: A Review

Pyrimidine and its derivatives are a very important class of heterocyclic compounds that show interesting applications in the field of medicinal chemistry. Pyrimidine not only plays an important role as an organic reaction intermediate but also has a wide range of interesting biological activities viz. antibacterial, antifungal, anticancer, anti-inflammatory, antiviral, and antiprotozoal activity, etc. Numerous methods are available for the formation of pyrimidine derivatives have been reported in the literature. The advantage of pyrimidine as a starting material for different therapeutically potent derivatives has given momentum to this research. This review aims to report the new work on the synthesis of marketed drugs which consist of pyrimidine moiety.

Synthesis of Bench-Stable N-Quaternized Ketene N,O-Acetals and Preliminary Evaluation as Reagents in Organic Synthesis

N-Quaternized ketene N,O-acetals are typically an unstable, transient class of compounds most commonly observed as reactive intermediates. In this report, we describe a general synthetic approach to a variety of bench-stable N-quaternized ketene N,O-acetals via treatment of pyridine or aniline bases with acetylenic ethers and an appropriate Brønsted or Lewis acid (triflic acid, triflimide, or scandium(III) triflate). The resulting pyridinium and anilinium salts can be used as reagents or synthetic intermediates in multiple reaction types. For example, N-(1-ethoxyvinyl)pyridinium or anilinium salts can thermally release highly reactive O-ethyl ketenium ions for use in acid catalyst-free electrophilic aromatic substitutions. N-(1-Ethoxyvinyl)-2-halopyridinium salts can be employed in peptide couplings as a derivative of Mukaiyama reagents or react with amines in nucleophilic aromatic substitutions under mild conditions. These preliminary reactions illustrate the broad potential of these currently understudied compounds in organic synthesis.

Nucleophilic C-H Etherification of Heteroarenes Enabled by Base-Catalyzed Halogen Transfer

We report a general protocol for the direct C-H etherification of N-heteroarenes. Potassium tert-butoxide catalyzes halogen transfer from 2-halothiophenes to N-heteroarenes to form N-heteroaryl halide intermediates that undergo tandem base-promoted alcohol substitution. Thus, the simple inclusion of inexpensive 2-halothiophenes enables regioselective oxidative coupling of alcohols with 1,3-azoles, pyridines, diazines, and polyazines under basic reaction conditions.

Late-stage C–H functionalization offers new opportunities in drug discovery

Over the past decade, the landscape of molecular synthesis has gained major impetus by the introduction of late-stage functionalization (LSF) methodologies. C-H functionalization approaches, particularly, set the stage for new retrosynthetic disconnections, while leading to improvements in resource economy. A variety of innovative techniques have been successfully applied to the C-H diversification of pharmaceuticals, and these key developments have enabled medicinal chemists to integrate LSF strategies in their drug discovery programmes. This Review highlights the significant advances achieved in the late-stage C-H functionalization of drugs and drug-like compounds, and showcases how the implementation of these modern strategies allows increased efficiency in the drug discovery process. Representative examples are examined and classified by mechanistic patterns involving directed or innate C-H functionalization, as well as emerging reaction manifolds, such as electrosynthesis and biocatalysis, among others. Structurally complex bioactive entities beyond small molecules are also covered, including diversification in the new modalities sphere. The challenges and limitations of current LSF methods are critically assessed, and avenues for future improvements of this rapidly expanding field are discussed. We, hereby, aim to provide a toolbox for chemists in academia as well as industrial practitioners, and introduce guiding principles for the application of LSF strategies to access new molecules of interest.

Development of Catalytic Reactions for Precise Control of Chemoselectivity

Catalytic chemoselective reactions of innately less reactive functionalities over more reactive functionalities are described. A cooperative catalyst comprising a soft Lewis acid/hard Brønsted base enabled chemoselective activation of a hydroxyl group over an amino group, allowing for nucleophilic addition to electron-deficient olefins. The reaction could be applicable for a variety of amino alcohols, including pharmaceuticals, without requiring a tedious protection-deprotection process. Chemoselective enolization and subsequent α-functionalization of carboxylic acid derivatives were also achieved by a redox active catalyst through the radical process, providing unnatural α-amino/hydroxy acid derivatives bearing a complex carbon framework and a diverse set of functionalities. The present chemoselective catalysis described herein offers new opportunities to expand the chemical space for innovative drug discovery research.

Silver-catalysed C–H bond activation: a recent review

Transition metal catalysed C–H activations are efficient, simple, mild, cost-effective and stereoselective, and many of them are environmentally sustainable transformations.

Addition of Fluorine and a Late-Stage Functionalization (LSF) of the Oral SERD AZD9833

Herein we describe our efforts using a late stage functionalization together with more traditional synthetic approaches to generate fluorinated analogues of the clinical candidate AZD9833. The effects of the addition of fluorine on the lipophilicity, permeability, and metabolism are discussed. Many of these changes were tolerated in terms of pharmacology and resulted in high quality molecules which reached advanced stages of profiling in the testing cascade.

Synthesis of new fluorescent molecules having an aggregation-induced emission property derived from 4-fluoroisoxazoles

Fluorescent molecules based on a fluorinated isoxazole scaffold were synthesized and investigated for their photochemical properties. The introduction of a fluorine substituent into 3,5-diarylisoxazoles led to an increase of fluorescence intensity and exhibited a redshift in the emission intensity. α-Fluorinated boron ketoiminates (F-BKIs) were also synthesized via a ring-opening reaction of 4-fluoroisoxazoles and exhibited highly fluorescent luminescence and aggregation-induced emission (AIE), showing promise as a new fluorophore.

Selective Halogenation of Pyridines Using Designed Phosphine Reagents

Halopyridines are key building blocks for synthesizing pharmaceuticals, agrochemicals, and ligands for metal complexes, but strategies to selectively halogenate pyridine C-H precursors are lacking. We designed a set of heterocyclic phosphines that are installed at the 4-position of pyridines as phosphonium salts and then displaced with halide nucleophiles. A broad range of unactivated pyridines can be halogenated, and the method is viable for late-stage halogenation of complex pharmaceuticals. Computational studies indicate that C-halogen bond formation occurs via an S_NAr pathway, and phosphine elimination is the rate-determining step. Steric interactions during C-P bond cleavage account for differences in reactivity between 2- and 3-substituted pyridines.

Selective C-H trifluoromethoxylation of (hetero)arenes as limiting reagent

Methods for direct C-H trifluoromethoxylation of arenes and heteroarenes are rare, despite the importance of trifluoromethoxylated compounds for pharmaceuticals, agrochemicals, and material sciences. Especially selective C-H trifluoromethoxylation of pyridines remains a formidable challenge. Here we show a general late-stage C-H trifluoromethoxylation of arenes and heteroarenes as limiting reagent with trifluoromethoxide anion. The reaction is mediated by silver salts under mild reaction conditions, exhibiting broad substrate scope and wide functional-group compatibility. In addition, ortho-position selective C-H trifluoromethoxylation of pyridines is observed. The method is not only applicable to the gram-scale synthesis of trifluoromethoxylated products but also allows efficient late-stage C-H trifluoromethoxylation of marketed small-molecule drugs, common pharmacophores and natural products.

Selective C-H trifluoromethoxylation of pyridines remains a formidable synthetic challenge. Here, the authors report a silver-mediated late-stage C-H trifluoromethoxylation of arenes and heteroarenes as limiting reagents with trifluoromethoxide anion.

A Unified and Practical Method for Carbon-Heteroatom Cross-Coupling using Nickel/Photo Dual Catalysis

While carbon-heteroatom cross-coupling reactions have been extensively studied, many methods are specific and limited to a particular set of substrates or functional groups. Reported here is a general method that allows for C-O, C-N and C-S cross-coupling reactions under one general set of conditions. We propose that an energy transfer pathway, in which an iridium photosensitizer produces an excited nickel(II) complex, is responsible for the key reductive elimination step that couples aryl bromides, iodides, and chlorides to 1° and 2° alcohols, amines, thiols, carbamates, and sulfonamides, and is amenable to scale up via a flow apparatus.

Current Advances in the Synthesis and Biological Evaluation of Pharmacologically Relevant 1,2,4,5-Tetrasubstituted-1H-Imidazole Derivatives

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In recent years, the synthesis and evaluation of the biological properties of 1,2,4,5-tetrasubstituted-1H-imidazole derivatives have been the subject of a large number of studies by academia and industry. In these studies it has been shown that this large and highly differentiated class of heteroarene derivatives includes high valuable compounds having important biological and pharmacological properties such as antibacterial, antifungal, anthelmintic, anti-inflammatory, anticancer, antiviral, antihypertensive, cholesterol-lowering, antifibrotic, antiuricemic, antidiabetic, antileishmanial and antiulcer activities.

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The present review with 411 references, in which we focused on the literature data published mainly from 2011 to 2017, aims to update the readers on the recent developments on the synthesis and biological evaluation of pharmacologically relevant 1,2,4,5-tetrasubstituted-1H-imidazole derivatives with an emphasis on their different molecular targets and their potential use as drugs to treat various types of diseases. Reference was also made to substantial literature data acquired before 2011 in this burgeoning research area.

The Fluorination of C-H Bonds: Developments and Perspectives

This Review summarizes advances in fluorination by C(sp² )-H and C(sp³ )-H activation. Transition-metal-catalyzed approaches championed by palladium have allowed the installation of a fluorine substituent at C(sp² ) and C(sp³ ) sites, exploiting the reactivity of high-oxidation-state transition-metal fluoride complexes combined with the use of directing groups (some transient) to control site and stereoselectivity. The large majority of known methods employ electrophilic fluorination reagents, but methods combining a nucleophilic fluoride source with an oxidant have appeared. External ligands have proven to be effective for C(sp³ )-H fluorination directed by weakly coordinating auxiliaries, thereby enabling control over reactivity. Methods relying on the formation of radical intermediates are complementary to transition-metal-catalyzed processes as they allow for undirected C(sp³ )-H fluorination. To date, radical C-H fluorinations mainly employ electrophilic N-F fluorination reagents but a unique Mn^III -catalyzed oxidative C-H fluorination using fluoride has been developed. Overall, the field of late-stage nucleophilic C-H fluorination has progressed much more slowly, a state of play explaining why C-H ¹⁸ F-fluorination is still in its infancy.

Anticancer-Active N-Heteroaryl Amines Syntheses: Nucleophilic Amination of N-Heteroaryl Alkyl Ethers with Amines

A mild amination protocol of N-heteroaryl alkyl ethers with various amines is described. This transformation is achieved by utilizing simple and readily available base as promoter via C-O bond cleavage, offering a new amination strategy to access several anticancer-active compounds. This work is highlighted by the excellent functional group compatibility, scalability, wide substrate scope, and easy derivatization of a variety of drugs.

Post-synthetic modification of covalent organic frameworks

This review is aimed at providing an in-depth understanding of the potential of post-synthetic strategies for the modification of covalent organic frameworks.

Copper(ii) facilitated decarboxylation for the construction of pyridyl–pyrazole skeletons

Pyridyl–pyrazole carboxylic compounds were synthesized in one step by Cu(ii) facilitated decarboxylation of H₃pdc and activation of pyridine in water.

Lewis acid promoted fluorine-alkoxy group exchange reactions for the synthesis of 5-alkoxy-4,4-difluoroisoxazoline systems

Lewis acid promoted substitution of fluorine yields novel 5-alkoxylated 4,4-difluoroisoxazolines via S_N1 type processes.

The Journey of HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) from Lab to Clinic

Human immunodeficiency virus (HIV) infection is now pandemic. Targeting HIV-1 reverse transcriptase (HIV-1 RT) has been considered as one of the most successful targets for the development of anti-HIV treatment. Among the HIV-1 RT inhibitors, non-nucleoside reverse transcriptase inhibitors (NNRTIs) have gained a definitive place due to their unique antiviral potency, high specificity, and low toxicity in antiretroviral combination therapies used to treat HIV. Until now, >50 structurally diverse classes of compounds have been reported as NNRTIs. Among them, six NNRTIs were approved for HIV-1 treatment, namely, nevirapine (NVP), delavirdine (DLV), efavirenz (EFV), etravirine (ETR), rilpivirine (RPV), and doravirine (DOR). In this perspective, we focus on the six NNRTIs and lessons learned from their journey through development to clinical studies. It demonstrates the obligatory need of understanding the physicochemical and biological principles (lead optimization), resistance mutations, synthesis, and clinical requirements for drugs.

Desymmetrization of cyclohexanes by site- and stereoselective C-H functionalization

Carbon-hydrogen (C-H) bonds have long been considered unreactive and are inert to traditional chemical reagents, yet new methods for the transformation of these bonds are continually being developed^1-9. However, it is challenging to achieve such transformations in a highly selective manner, especially if the C-H bonds are unactivated¹⁰ or not adjacent to a directing group^11-13. Catalyst-controlled site-selectivity-in which the inherent reactivities of the substrates¹⁴ can be overcome by choosing an appropriate catalyst-is an appealing concept, and substantial effort has been made towards catalyst-controlled C-H functionalization^6,15-17, in particular methylene C-H bond functionalization. However, although several new methods have targeted these bonds in cyclic alkanes, the selectivity has been relatively poor^18-20. Here we illustrate an additional level of sophistication in catalyst-controlled C-H functionalization, whereby unactivated cyclohexane derivatives can be desymmetrized in a highly site- and stereoselective manner through donor/acceptor carbene insertion. These studies demonstrate the potential of catalyst-controlled site-selectivity to govern which C-H bond will react, which could enable new strategies for the production of fine chemicals.