A visible-light-promoted radical reaction system for azidation and halogenation of tertiary aliphatic C-H bonds

Preparation of a benziodazole-type iodine(III) compound and its application as a nitrating reagent for synthesis of furazans via a copper-catalyzed cascade process

The existing hypervalent I(III) reagents bearing ONO2 group are limited in types and their applications primarily focused on the nitrooxylation reactions featuring a fully-exo fashion. Herein, a benziodazole-type O2NO-I(III) compound was prepared and its reaction with β-monosubstituted enamines in the presence of CuI could trigger a radical nitration/cyclization/dehydration cascade to provide a series of less explored but biologically interesting furazan heterocycles. Mechanistically, the benziodazole-type O2NO-I(III) compound acts as a nitrating reagent and incorporates its NO moiety into the final furazan product in a fully-endo model, a process of which was proposed to involve nitration, cyclization and dehydration.

Total synthesis of naturally occurring abietane diterpenoids via a late-stage Fe(iii)-bTAML catalysed Csp3-H functionalization

The synthesis of diverse trans-fused decalins, including the abietane diterpenoids scaffold, using an efficient selective oxidation strategy is described. The abietane core was demonstrated to be a versatile scaffold that can be site-selectively functionalized. The utility of this novel oxidation strategy was showcased in a concise total synthesis of six abietane congeners.

Markovnikov Hydrochlorination of Unactivated Alkenes with FeCl3 via a HAT/XAT Sequence

Hydrochlorination of alkenes is a practical strategy for accessing organic chlorides. Herein, we report the hydrochlorination of unactivated alkenes via a hydrogen atom transfer/halogen atom transfer process using earth-abundant and biocompatible FeCl3 as a chlorine source under extraordinarily mild reaction conditions. The protocol is easy to operate with notable features such as excellent chemoselectivity, remarkable efficiency, a broad substrate scope, and good functional group tolerance. Importantly, the synthetic utility is highlighted by scaled-up reactions, late-stage derivatizations of products, and the modification of sulfonamides.

Recent Advances in Photoinduced Modification of Amino Acids, Peptides, and Proteins

The chemical modification of biopolymers like peptides and proteins is a key technology to access vaccines and pharmaceuticals. Similarly, the tunable derivatization of individual amino acids is important as they are key building blocks of biomolecules, bioactive natural products, synthetic polymers, and innovative materials. The high diversity of functional groups present in amino acid-based molecules represents a significant challenge for their selective derivatization Recently, visible light-mediated transformations have emerged as a powerful strategy for achieving chemoselective biomolecule modification. This technique offers numerous advantages over other methods, including a higher selectivity, mild reaction conditions and high functional-group tolerance. This review provides an overview of the most recent methods covering the photoinduced modification for single amino acids and site-selective functionalization in peptides and proteins under mild and even biocompatible conditions. Future challenges and perspectives are discussed beyond the diverse types of photocatalytic transformations that are currently available.

Divergent Reactivity of 1,2,3-Benzotriazin-4(3H)-ones: Photocatalytic Synthesis of 3-Substituted Isoindolinones Achieved through a Nitrogen-Mediated Hydrogen Atom Shift

A regioselective visible-light-mediated denitrogenative alkene insertion of 1,2,3-benzotriazin-4(3H)-ones was developed to access 3-substituted isoindolinones, an important structural motif present in many biologically active molecules and natural products. Notably, divergent reactivity was achieved by switching from reported nickel catalysis (where C3-substituted 3,4-dihydroisoquinolin-1(2H)-ones form) to photocatalysis, where photocatalytic denitrogenation and a subsequent nitrogen-mediated hydrogen atom shift lead to exclusive 3-substituted isoindolinone formation. The developed photocatalytic reaction is compatible with activated terminal alkenes and cyclic α,β-unsaturated esters and ketones, with wide functional group tolerance for N-substitution of the 1,2,3-benzotriazin-4(3H)-ones. The utility of this procedure is highlighted by a gram-scale synthesis and postsynthetic amidation. To understand the origin of this unique product selectivity, experimental and computational mechanistic studies were performed.

Enantioselective catalytic radical decarbonylative azidation and cyanation of aldehydes

Empowered by the ubiquity of carbonyl functional groups in organic compounds, decarbonylative functionalization was prevalent in the construction of complex molecules. Under this context, asymmetric decarbonylative functionalization has emerged as an efficient pathway to accessing chiral motifs. However, ablation of enantiomeric control in a conventional 2e transition metal-catalyzed process was notable because of harsh conditions (high temperatures, etc.) that are usually required. To address this challenge and use readily accessible aldehyde directly, we report the asymmetric radical decarbonylative azidation and cyanation. Diverse aldehydes were directly used as alkyl radical precursor, engaging in the subsequent inner-sphere or outer-sphere ligand transfer where functional motifs (CN and N3) could be incorporated in excellent site- and enantioselectivity. Mild conditions, broad scope, excellent regioselectivity (driven by polarity-matching strategy), and enantioselectivity were shown for both transformations. This radical decarbonylative strategy using aldehydes as alkyl radical precursor has offered a powerful reaction manifold in asymmetric radical transformations to construct functional motifs regio- and stereoselectively.

Synthesis of Chlorinated Oligopeptides via γ- and δ-Selective Hydrogen Atom Transfer Enabled by the N-Chloropeptide Strategy

The introduction of a chlorine atom could potentially endow peptide derivatives with notable bioactivity and applicability. However, despite considerable recent progress in C(sp3)-H functionalization chemistry, a general method for the site-selective chlorination of inert aliphatic C-H bonds in peptides still remains elusive. Herein, we report a site-selective C(sp3)-H chlorination of oligopeptides based on an N-chloropeptide strategy. N-chloropeptides, which are easily prepared from the corresponding native oligopeptides, are smoothly degraded in the presence of an appropriate copper catalyst, and a subsequent 1,5-hydrogen atom transfer affords γ- or δ-chlorinated peptides in excellent yield. A wide variety of amino acid residues can thus be site-selectively chlorinated in a predictable manner. This method hence enables the efficient synthesis of otherwise less accessible, chlorine-containing peptide fragments of natural peptides. We moreover demonstrate here the successful estimation of the stereochemistry of the chlorinated carbon atom in aquimarin A. Furthermore, we reveal that side-chain-chlorinated peptides can serve as highly useful substructures with a fine balance between stability and reactivity, which renders them promising targets for synthetic and medicinal applications.

Decatungstate-Catalyzed C(sp3)-H Alkylation of a Val Residue Proximal to the N-Terminus Controlled by an Electrostatic Interaction

The decatungstate photocatalyst [W₁₀O₃₂]^4- efficiently promoted the C(sp³)-H alkylation of the trifluoroacetic acid salt of valine methyl ester (H-Val-OMe·TFA) with electron-deficient alkenes under UV irradiation. The electrostatic interaction between the cationic ammonium group (⁺NH₃) of the main chain and anionic [W₁₀O₃₂]^4- played an important role in this reaction. The influence of various protected amino acids in the C(sp³)-H alkylation was investigated as the model reaction for the alkylation of Val-containing peptides. The introduction of an alkyne moiety into Val through this alkylation was successful, and successive copper-catalyzed azide-alkyne cycloaddition (CuAAC) was demonstrated. The C(sp³)-H bond of a Val residue located at the second from the N-terminus was also successfully converted. C(sp³)-H alkylation of oligopeptides containing two Val residues selectively proceeded proximally to the N-terminus.

Taming Bromine Azide for Use in Organic Solvents─Radical Bromoazidations and Alcohol Oxidations

The formation of bromine azide from the bisazidobromate(I) anion or alternatively from Zhdankin's reagent, using a phosphonium bromide salt as a common starting point, is reported. After homolytic cleavage in the presence of alkenes or alcohols either 1,2-functionalization or alternatively the selective oxidation of secondary alcohols in the presence of primary alcohols occur. The scopes and limitations of the use of BrN₃ are covered.

Merging Copper(I) Photoredox Catalysis and Iodine(III) Chemistry for the Oxy-monofluoromethylation of Alkenes

A simple process for the oxy-monofluoromethylation of alkenes is described. In combination with visible-light copper(I) photoredox catalysis, an easily accessible iodine(III) reagent containing monofluoroacetoxy ligands serves as a powerful source of a monofluoromethyl (CH₂ F) radical, enabling the step economical synthesis of γ-fluoro-acetates from a broad range of olefinic substrates under mild conditions. Applications to late-stage diversification of alkenes derived from complex molecules, amino acids and the synthesis of fluoromethylated heterocycles are also demonstrated.

Photocatalytic Late-Stage C-H Functionalization

The emergence of modern photocatalysis, characterized by mildness and selectivity, has significantly spurred innovative late-stage C-H functionalization approaches that make use of low energy photons as a controllable energy source. Compared to traditional late-stage functionalization strategies, photocatalysis paves the way toward complementary and/or previously unattainable regio- and chemoselectivities. Merging the compelling benefits of photocatalysis with the late-stage functionalization workflow offers a potentially unmatched arsenal to tackle drug development campaigns and beyond. This Review highlights the photocatalytic late-stage C-H functionalization strategies of small-molecule drugs, agrochemicals, and natural products, classified according to the targeted C-H bond and the newly formed one. Emphasis is devoted to identifying, describing, and comparing the main mechanistic scenarios. The Review draws a critical comparison between established ionic chemistry and photocatalyzed radical-based manifolds. The Review aims to establish the current state-of-the-art and illustrate the key unsolved challenges to be addressed in the future. The authors aim to introduce the general readership to the main approaches toward photocatalytic late-stage C-H functionalization, and specialist practitioners to the critical evaluation of the current methodologies, potential for improvement, and future uncharted directions.

Synthesis of Ynones via N-Iodosuccinimide-Mediated Oxidation of Propargyl Alcohols under Mild Conditions

A convenient and mild approach for the construction of ynones via N-iodosuccinimide (NIS)-mediated oxidation of propargyl alcohols has been described. This reaction could furnish the ynone products with a diversity of functional groups in moderate to excellent yields, and the flexibility of this method was demonstrated by the gram-scale experiment and further transformation.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Photocatalytic C(sp3) radical generation via C-H, C-C, and C-X bond cleavage

C(sp³) radicals (R˙) are of broad research interest and synthetic utility. This review collects some of the most recent advancements in photocatalytic R˙ generation and highlights representative examples in this field. Based on the key bond cleavages that generate R˙, these contributions are divided into C–H, C–C, and C–X bond cleavages. A general mechanistic scenario and key R˙-forming steps are presented and discussed in each section.

C(sp³) radicals (R˙) are of broad research interest and synthetic utility.

N ‐Terminal Selective C−H Azidation of Proline‐Containing Peptides: a Platform for Late‐Stage Diversification

A methodology for the C−H azidation of N‐terminal proline‐containing peptides was developed employing only commercially available reagents. Peptides bearing a broad range of functionalities and containing up to 6 amino acids were selectively azidated at the carbamate‐protected N‐terminal residue in presence of the numerous other functional groups present on the molecules. Post‐functionalizations of the obtained aminal compounds were achieved: cycloaddition reactions or C−C bond formations via a sequence of imine formation/nucleophilic addition were performed, offering an easy access to diversified peptides.

Synthesis of Visible-Light-Activated Hypervalent Iodine and Photo-oxidation under Visible Light Irradiation via a Direct S0→Tn Transition

Heavy atom-containing molecules cause a photoreaction by a direct S₀ → T_n transition. Therefore, even in a hypervalent iodine compound with a benzene ring as the main skeleton, the photoreaction proceeds under 365-400 nm wavelength light, where UV-visible spectra are not observed by usual measurement method. Some studies, however, report hypervalent iodine compounds that strongly absorb visible light. Herein, we report the synthesis of two visible light-absorbing hypervalent iodines and their photooxidation properties under visible light irradiation. We also demonstrated that the S₀ → T_n transition causes the photoreaction to proceed under wavelengths in the blue and green light region.

Electronic control over site-selectivity in hydrogen atom transfer (HAT) based C(sp3)-H functionalization promoted by electrophilic reagents

The direct functionalization of C(sp³)-H bonds represents one of the most investigated approaches to develop new synthetic methodology. Among the available strategies for intermolecular C-H bond functionalization, increasing attention has been devoted to hydrogen atom transfer (HAT) based procedures promoted by radical or radical-like reagents, that offer the opportunity to introduce a large variety of atoms and groups in place of hydrogen under mild conditions. Because of the large number of aliphatic C-H bonds displayed by organic molecules, in these processes control over site-selectivity represents a crucial issue, and the associated factors have been discussed. In this review article, attention will be devoted to the role of electronic effects on C(sp³)-H bond functionalization site-selectivity. Through an analysis of the recent literature, a detailed description of the HAT reagents employed in these processes, the associated mechanistic features and the selectivity patterns observed in the functionalization of substrates of increasing structural complexity will be provided.

Selective desaturation of amides: a direct approach to enamides

C(sp³)–H bond desaturation has been an attractive strategy in organic synthesis. Enamides are important structural fragments in pharmaceuticals and versatile synthons in organic synthesis. However, the dehydrogenation of amides usually occurs on the acyl side benefitting from enolate chemistry like the desaturation of ketones and esters. Herein, we demonstrate an Fe-assisted regioselective oxidative desaturation of amides, which provides an efficient approach to enamides and β-halogenated enamides.

A novel and regioselective N-α,β-desaturation and dehydrogenative N-β-halogenation of amides was developed. This chemistry with high selectivity and broad substrate scope provides an efficient approach to enamides from simple amides.

Hypervalent-iodine promoted selective cleavage of C(sp3)–C(sp3) bonds in ethers

A visible-light-promoted and radical-mediated strategy for the site-specific cleavage of C(sp3)–C(sp3) bonds in ethers is reported.

Decatungstate-photocatalysed C(sp3)-H azidation

C–H Azidation is an increasingly important tool for bioconjugation, materials chemistry, and the synthesis of nitrogen-containing natural products. While several approaches have been developed, these often require exotic and energetic...

Visible-Light-Induced Catalytic Selective Halogenation with Photocatalyst

Halide moieties are essential structures of compounds in organic chemistry due to their popularity and wide applications in many fields such as natural compounds, agrochemicals, and pharmaceuticals. Thus, many methods have been developed to introduce halides into various organic molecules. Recently, visible-light-driven reactions have emerged as useful methods of organic synthesis. Particularly, halogenation strategies using visible light have significantly improved the reaction efficiency and reduced toxicity, as well as promoted reactions under mild conditions. In this review, we have summarized recent studies in visible-light-mediated halogenation (chlorination, bromination, and iodination) with photocatalysts.

Photoinduced C(sp3)-H chlorination of amides with tetrabutyl ammonium chloride

A new protocol was developed for the site-selective C(sp³)-H chlorination of amides with tetrabutyl ammonium chloride as the chlorinating agent. The reaction features a tandem sequence that involves a (diacetoxyiodo)benzene-mediated and chloride anion-involved N-H chlorination followed by photoinitiated chlorine atom transfer. A wide variety of carboxamides and sulfonamides were chlorinated at the δ-position by using this method.

Hypervalent Iodine-Mediated Late-Stage Peptide and Protein Functionalization

Hypervalent iodine compounds are powerful reagents for the development of novel transformations. As they exhibit low toxicity, high functional group tolerance, and stability in biocompatible media, they have been used for the functionalization of biomolecules. Herein, we report recent advances up to June 2021 in peptide and protein modification using hypervalent iodine reagents. Their use as group transfer or oxidizing reagents is discussed in this Minireview, including methods targeting polar, aromatic, or aliphatic amino acids and peptide termini.

Mechanistic Investigation of the Iron-Catalyzed Azidation of Alkyl C(sp3)-H Bonds with Zhdankin's λ3-Azidoiodane

An in-depth study of the mechanism of the azidation of C(sp³)-H bonds with Zhdankin's λ³-azidoiodane reagent catalyzed by iron(II)(pybox) complexes is reported. Previously, it was shown that tertiary and benzylic C(sp³)-H bonds of a range of complex molecules underwent highly site-selective azidation by reaction with a λ³-azidoiodane reagent and an iron(II)(pybox) catalyst under mild conditions. However, the mechanism of this reaction was unclear. Here, a series of mechanistic experiments are presented that reveal critical features responsible for the high selectivity and broad scope of this reaction. These experiments demonstrate the ability of the λ³-azidoiodane reagent to undergo I-N bond homolysis under mild conditions to form λ²-iodanyl and azidyl radicals that undergo highly site-selective and rate-limiting abstraction of a hydrogen atom from the substrate. The resultant alkyl radical then combines rapidly with a resting state iron(III)-azide complex, which is generated by the reaction of the λ³-azidoiodane with the iron(II)(pybox) complex, to form the C(sp³)-N₃ bond. This mechanism is supported by the independent synthesis of well-defined iron complexes characterized by cyclic voltammetry, X-ray diffraction, and EPR spectroscopy, and by the reaction of the iron complexes with alkanes and the λ³-azidoiodane. Reaction monitoring and kinetic studies further reveal an unusual effect of the catalyst on the rate of formation of product and consumption of reactants and suggest a blueprint for the development of new processes leading to late-stage functionalization of C(sp³)-H bonds.

The azidosulfonylation of terminal alkynes leading to β-azidovinyl sulfones

We report herein the first example of the N₃ radical-mediated azidosulfonylation of alkynes, affording the β-azidovinyl sulfone products with a broad substrate scope, excellent functional group compatibility, and high yield. DFT calculations suggest that the mechanism of the reaction proceeds through an unprecedented sequential N₃ radical addition and sulfonyl radical coupling pathway.

Copper-Catalyzed Intermolecular Functionalization of Unactivated C(sp3)-H Bonds and Aliphatic Carboxylic Acids

Intermolecular functionalization of C(sp³)-H bonds and aliphatic carboxylic acids enables the efficient synthesis of high value-added organic compounds from readily available starting materials. Although methods involving hydrogen atom transfer have been developed for such functionalization, these methods either work for only activated C(sp³)-H bonds or bring in a narrow set of functional groups. Here we describe a Cu-catalyzed process for the diverse functionalization of both unactivated C(sp³)-H bonds and aliphatic carboxylic acids. The process is enabled by the trapping of alkyl radicals generated through hydrogen atom abstraction by arylsulfonyl-based SOMO-philes, which introduces a large array of C, N, S, Se, and halide-based functional groups. The chemoselectivity can be switched from C-H functionalization to decarboxylative functionalization by matching the bond dissociation energy of the hydrogen atom transfer reagent with that of the target C-H or O-H bond.

Recent Advances in C–Br Bond Formation

Organobromine compounds are extremely useful in organic synthesis. In this perspective, a focused discussion on some recent advancements in C–Br bond-forming reactions is presented.

1 Introduction

2 Selected Recent Advances

2.1 Catalytic Asymmetric Bromopolycyclization of Olefinic Substrates

2.2 Catalytic Asymmetric Intermolecular Bromination

2.3 Some New Catalysts and Reagents for Bromination

2.4 Catalytic Site-Selective Bromination of Aromatic Compounds

2.5 sp3 C–H Bromination via Atom Transfer/Cross-Coupling

3 Outlook

Structure and Reactivity of N-Heterocyclic Alkynyl Hypervalent Iodine Reagents

Ethynylbenziodoxol(on)e (EBX) cyclic hypervalent iodine reagents have become popular reagents for the alkynylation of radicals and nucleophiles, but only offer limited possibilities for further structure and reactivity fine-tuning. Herein, the synthesis of new N-heterocyclic hypervalent iodine reagents with increased structural flexibility based on amide, amidine and sulfoximine scaffolds is reported. Solid-state structures of the reagents are reported and the analysis of the I-Calkyne bond lengths allowed assessing the trans-effect of the different substituents. Molecular electrostatic potential (MEP) maps of the reagents, derived from DFT computations, revealed less pronounced σ-hole regions for sulfonamide-based compounds. Most reagents reacted well in the alkynylation of β-ketoesters. The alkynylation of thiols afforded more variable yields, with compounds with a stronger σ-hole reacting better. In metal-mediated transformations, the N-heterocyclic hypervalent iodine reagents gave inferior results when compared to the O-based EBX reagents.

Manganese/bipyridine-catalyzed non-directed C(sp3)-H bromination using NBS and TMSN3

A Mn(II)/bipyridine-catalyzed bromination reaction of unactivated aliphatic C(sp³)−H bonds has been developed using N-bromosuccinimide (NBS) as the brominating reagent. The reaction proceeded in moderate-to-good yield, even on a gram scale. The introduced bromine atom can be converted into fluorine and allyl groups.

Highly chemoselective synthesis of hindered amides via cobalt-catalyzed intermolecular oxidative hydroamidation

α-Tertiary amides are of great importance for medicinal chemistry. However, they are often challenging to access through conventional methods due to reactivity and chemoselectivity issues. Here, we report a single-step approach towards such amides via cobalt-catalyzed intermolecular oxidative hydroamidation of unactivated alkenes, using nitriles of either solvent- or reagent-quantities. This protocol is selective for terminal alkenes over groups that rapidly react under known carbocation amidation conditions such as tertiary alcohols, electron-rich alkenes, ketals, weak C−H bonds, and carboxylic acids. Straightforward access to a diverse array of hindered amides is demonstrated, including a rapid synthesis of an aminoadamantane-derived pharmaceutical intermediate.

α-Tertiary amides are common in bioactive natural products and pharmaceuticals, but challenging to access by conventional methods. Here, the authors report a single-step approach toward α-tertiary amides via cobalt-catalyzed intermolecular oxidative hydroamidation of unactivated alkenes.

Site Selective Chlorination of C(sp3 )-H Bonds Suitable for Late-Stage Functionalization

C(sp³ )-Cl bonds are present in numerous biologically active small molecules, and an ideal route for their preparation is by the chlorination of a C(sp³ )-H bond. However, most current methods for the chlorination of C(sp³ )-H bonds are insufficiently site selective and tolerant of functional groups to be applicable to the late-stage functionalization of complex molecules. We report a method for the highly selective chlorination of tertiary and benzylic C(sp³ )-H bonds to produce the corresponding chlorides, generally in high yields. The reaction occurs with a mixture of an azidoiodinane, which generates a selective H-atom abstractor under mild conditions, and a readily-accessible and inexpensive copper(II) chloride complex, which efficiently transfers a chlorine atom. The reaction's exceptional functional group tolerance is demonstrated by the chlorination of >30 diversely functionalized substrates and the late-stage chlorination of a dozen derivatives of natural products and active pharmaceutical ingredients.

Practical Synthesis of 2-Iodosobenzoic Acid (IBA) without Contamination by Hazardous 2-Iodoxybenzoic Acid (IBX) under Mild Conditions

We report a convenient and practical method for the preparation of nonexplosive cyclic hypervalent iodine(III) oxidants as efficient organocatalysts and reagents for various reactions using Oxone® in aqueous solution under mild conditions at room temperature. The thus obtained 2-iodosobenzoic acids (IBAs) could be used as precursors of other cyclic organoiodine(III) derivatives by the solvolytic derivatization of the hydroxy group under mild conditions of 80 °C or lower temperature. These sequential procedures are highly reliable to selectively afford cyclic hypervalent iodine compounds in excellent yields without contamination by hazardous pentavalent iodine(III) compound.

Manganese-Catalyzed Electrochemical Tandem Azidation-Coarctate Reaction: Easy Access to 2-Azo-benzonitriles

A one-pot cascade transformation consisting of an electrochemically driven azidation of 2H-indazole followed by coarctate fragmentation is developed to synthesize the 2-azo-benzonitrile motif. This manganese-catalyzed transformation is external-chemical-oxidant-free and operates at ambient temperature under air. This methodology exhibits good functional group tolerance, affording a broad range of substrate scopes of up to 89% isolated yield. Diverse derivatization of the 2-azo-benzonitrile product resulted in other valuable scaffolds.

Radical-Based Synthesis and Modification of Amino Acids

Amino acids (AAs) are key structural motifs with widespread applications in organic synthesis, biochemistry, and material sciences. Recently, with the development of milder and more versatile radical-based procedures, the use of strategies relying on radical chemistry for the synthesis and modification of AAs has gained increased attention, as they allow rapid access to libraries of novel unnatural AAs containing a wide range of structural motifs. In this Minireview, we provide a broad overview of the advancements made in this field during the last decade, focusing on methods for the de novo synthesis of α-, β-, and γ-AAs, as well as for the selective derivatisation of canonical and non-canonical α-AAs.

Asymmetric α-Chlorination of β-Keto Esters Using Hypervalent Iodine-Based Cl-Transfer Reagents in Combination with Cinchona Alkaloid Catalysts

We herein report an unprecedented strategy for the asymmetric α-chlorination of β-keto esters with hypervalent iodine-based Cl-transfer reagents using simple Cinchona alkaloid catalysts. Our investigations support an α-chlorination mechanism where the Cinchona species serves as a nucleophilic catalyst by reacting with the chlorinating agent to generate a chiral electrophilic Cl-transfer reagent in situ. Using at least 20 mol-% of the alkaloid catalyst allows for good yields and enantioselectivities for a variety of different β-keto esters under operationally simple conditions.

Mangana(iii/iv)electro-catalyzed C(sp3)-H azidation

Manganaelectro-catalyzed azidation of otherwise inert C(sp³)-H bonds was accomplished using most user-friendly sodium azide as the nitrogen-source. The operationally simple, resource-economic C-H azidation strategy was characterized by mild reaction conditions, no directing group, traceless electrons as the sole redox-reagent, Earth-abundant manganese as the catalyst, high functional-group compatibility and high chemoselectivity, setting the stage for late-stage azidation of bioactive compounds. Detailed mechanistic studies by experiment, spectrophotometry and cyclic voltammetry provided strong support for metal-catalyzed aliphatic radical formation, along with subsequent azidyl radical transfer within a manganese(iii/iv) manifold.

Visible light photocatalysis in the late-stage functionalization of pharmaceutically relevant compounds

The late stage functionalization (LSF) of complex biorelevant compounds is a powerful tool to speed up the identification of structure-activity relationships (SARs) and to optimize ADME profiles. To this end, visible-light photocatalysis offers unique opportunities to achieve smooth and clean functionalization of drugs by unlocking site-specific reactivities under generally mild reaction conditions. This review offers a critical assessment of current literature, pointing out the recent developments in the field while emphasizing the expected future progress and potential applications. Along with paragraphs discussing the visible-light photocatalytic synthetic protocols so far available for LSF of drugs and drug candidates, useful and readily accessible synoptic tables of such transformations, divided by functional groups, will be provided, thus enabling a useful, fast, and easy reference to them.

Recent Advances in Rapid Synthesis of Non-proteinogenic Amino Acids from Proteinogenic Amino Acids Derivatives via Direct Photo-Mediated C-H Functionalization

Non-proteinogenic amino acids have attracted tremendous interest for their essential applications in the realm of biology and chemistry. Recently, rising C-H functionalization has been considered an alternative powerful method for the direct synthesis of non-proteinogenic amino acids. Meanwhile, photochemistry has become popular for its predominant advantages of mild conditions and conservation of energy. Therefore, C-H functionalization and photochemistry have been merged to synthesize diverse non-proteinogenic amino acids in a mild and environmentally friendly way. In this review, the recent developments in the photo-mediated C-H functionalization of proteinogenic amino acids derivatives for the rapid synthesis of versatile non-proteinogenic amino acids are presented. Moreover, postulated mechanisms are also described wherever needed.