Photoinduced Regiodivergent and Enantioselective Cross-Coupling of Glycine Derivatives with Hydrocarbon Feedstocks

Regiodivergent asymmetric synthesis represents a transformative strategy for the efficient generation of structurally diverse chiral products from a single set of starting materials, significantly enriching their enantiomeric composition. However, the design of radical-mediated regiodivergent and enantioselective reactions that can accommodate a wide range of functional groups and substrates has posed significant challenges. The obstacles primarily lie in switching the regioselectivity and achieving high enantiodiscrimination, especially when dealing with high-energy intermediates. To address these issues, we have developed a new catalytic system that integrates photoinduced hydrogen atom transfer (HAT) and chiral copper catalysis, involving the fine-tuning of chiral ligands, additives, and other reaction parameters. The strategy facilitates regiodivergent and enantioselective cross-couplings between N-aryl glycine ester/amide derivatives and abundant hydrocarbon feedstocks through strong C(sp3)-H bond activation. This approach allows for the controlled and stereoselective formation of C(sp3)-C(sp3) and C(sp3)-N bonds, yielding a rich variety of C- or N-alkylated glycine esters and amides with commendable yields (up to 92% yield), exclusive regioselectivities (typically >20:1 rr), and high enantioselectivities (up to 96% ee). Our methodology not only provides a promising avenue for the stereoselective incorporation of alkyl functionalities onto specific sites of biologically significant molecules but also offers a practical approach for regioselectivity switching while simultaneously achieving high asymmetric induction within photochemical reactions.

Applications of innovative synthetic strategies in anticancer drug discovery: The driving force of new chemical reactions

The discovery of novel anticancer agents remains a critical goal in medicinal chemistry, with innovative synthetic methodologies playing a pivotal role in advancing this field. Recent breakthroughs in CH activation reactions, cyclization reactions, multicomponent reactions, cross-coupling reactions, and photo- and electro-catalytic reactions have enabled the efficient synthesis of new molecular scaffolds exhibiting potent biological activities, including anticancer properties. These methodologies have facilitated the functionalization of natural products, the modification of bioactive molecules, and the generation of entirely new compounds, many of which demonstrate strong antitumor activity. This review summarizes the latest synthetic strategies employed over the past five years for discovering anticancer agents, focusing on their influence on drug design. Additionally, the role of new chemical reactions in expanding chemical space and overcoming challenges, such as drug resistance and selectivity, is highlighted, further emphasizing the importance of discovering novel reactions as a key trend in future drug development.

Transition metal-catalyzed cascade C-H activation/cyclization with alkynes: an update on sulfur-containing directing groups

In light of the extensive applications of sulfur-containing heterocyclic compounds in drug discovery, agrochemicals, and advanced materials, the construction of complex sulfur-containing molecular scaffolds has flourished in recent years. There is a profound interest in synthetic methods for forming carbon-sulfur bonds. Regarding this, transition metal (TM)-catalyzed C-H bond activation has emerged as a valuable means for the rapid formation of C-S bonds, although it is comparatively less explored than C-N or C-C bonds. The research significance of sulfur-directed C-H activation chemistry lies in maintaining a balance between activating and poisoning the catalyst as well as in the diversity and novelty of its properties. This review centers on sulfur-directed TM-catalyzed cascade C-H activation/cyclization with alkyne and encompasses the literature mainly from 2012 to 2024. The widely acknowledged reactivity and versatility of rhodium, ruthenium, and cobalt catalysts have given rise to various captivating cascade processes. For most reactions illustrated in this review, reactivity and selectivity are attained through the flexible synergistic combination of different metal catalysts and additives. Further advancements will be accompanied with the discovery of innovative sulfur-directing groups, chiral catalysis, and ground-breaking experimental techniques. This article will also inspire researchers to gain a deeper understanding of the mechanism, thus undoubtedly leading to innovations and more discoveries in the future.

Co(III) or Ru(II)-Catalyzed Selective C-H Alkynylation of 2-Pyridones and Their Derivatives with Bromoalkynes

We successfully reported selective C-H alkynylation of 2-pyridones with bromoalkynes under the catalysis of Co(III) or Ru(II). The alkynylation reaction used easily accessible bromoalkynes instead of high-valent iodine alkynes. There is a broad substrate scope of 2-pyridones with good yields. In addition, 2-pyridone can be used as a weakly directing group for C-H alkynylation of the proximal aryl C-H bond. This method offers an efficient approach for synthesizing diverse 2-pyridone derivatives, yielding alkynylated products up to 95% yield (>40 examples).

Redox Active vs Redox Neutral in Ru/Pd-Catalyzed Sulfonylation: Theoretical Insights into Structure-Activity Relationship between Metal Centers and Regio-Selectivity

The structure-activity relationship between the metal center and regio-selectivity is persistently a pivotal scientific issue. To address this, we select the 2-phenylpyridine sulfonylation reactions catalyzed by ruthenium and palladium as research subjects. An extensive theoretical study has been conducted on their reaction mechanisms, the sources of regio-selectivity, and the evolution of electronic structures. The distinct electronic structures lead to completely different catalytic mechanisms and electronic structure evolution processes for ruthenium and palladium. Ruthenium tends to form six-coordinate octahedral complexes, thus undergoing an inner-sphere redox active Ru(II)-Ru(III)-Ru(IV)-Ru(II) catalytic cycle. In contrast, palladium tends to form four-coordinate planar quadrilateral complexes, hence undergoing an outer-sphere redox neutral Pd(II) catalytic cycle. The distinct electronic structure evolution processes fundamentally differentiate the radical attack modes in the sulfonation process, thereby determining the regio-selectivity of the reaction. In the Ru-catalyzed system, the meta-selectivity arises mainly from a more stable Schrock carbene-type meta-intermediate. For the Pd-catalyzed system, the ortho-selectivity mainly comes from the stabilizing effect of the Pd(II) center on the single electron. This study provides novel insights into how the electronic structure of metal centers influences the reaction mechanism and selectivity, making a theoretical contribution to a deeper comprehension of the mechanism and regio-selectivity underlying aromatic functionalization reactions.

Tungsten-catalyzed stereodivergent isomerization of terminal olefins

Catalytic alkene isomerization is a powerful synthetic strategy for preparing valuable internal alkenes from simple feedstocks. The utility of olefin isomerization hinges on the ability to control both positional and stereoisomerism to access a single product among numerous potential isomers. Within base-metal catalysis, relatively little is known about how to modulate reactivity and selectivity with group 6 metal-catalyzed isomerization. Here, we describe a tungsten-catalyzed, positionally selective alkene isomerization reaction in which tuning the ligand environment grants access to either the E- or Z-stereoisomer. The reactions employ simple, commercially available precatalysts and ligands. Preliminary mechanistic studies suggest that the ligand environment around 7-coordinate tungsten is crucial for stereoselectivity, and that substrate directivity prevents over-isomerization to the conjugated alkene. These features allow for exclusive formation of β,γ-unsaturated carbonyl compounds that are otherwise difficult to prepare.

Pd-Catalyzed Hydrocyanation of Methylenecyclopropanes: A Highly Selective Ring-Opening Access to 2-Substituted Allylic Nitriles

Transition-metal-catalyzed hydrofunctionalization of methylenecyclopropanes presents a useful but challenging transformation due to the complex selectivity and multiple reaction pathways. We describe herein an unprecedented highly efficient and selective palladium-catalyzed hydrocyanation of methylenecyclopropanes to give various 2-substituted allylic nitriles. Mechanistic studies demonstrated that the transformation may undergo Markovnikov-type hydrometalation and β-carbon elimination.

Direct Benzylic C-H Etherification Enabled by Base-Promoted Halogen Transfer

We disclose a benzylic C-H oxidative coupling reaction with alcohols that proceeds through a synergistic deprotonation, halogenation and substitution sequence. The combination of tert-butoxide bases with 2-halothiophene halogen oxidants enables the first general protocol for generating and using benzyl halides through a deprotonative pathway. In contrast to existing radical-based methods for C-H functionalization, this process is guided by C-H acidity trends. This gives rise to new synthetic capabilities, including the ability to functionalize diverse methyl(hetero)arenes, tolerance of oxidizable and nucleophilic functional groups, precision site-selectivity for polyalkylarenes and use of a double C-H etherification process to controllably oxidize methylarenes to benzaldehydes.

Computational Design of Ligands for the Ir-Catalyzed C5-Borylation of Indoles through Tuning Dispersion Interactions

The indole moiety is ubiquitous in natural products and pharmaceuticals. C-H borylation of the benzenoid moiety of indoles is a challenging task, especially at the C5 position. We have combined computational and experimental studies to introduce multiple noncovalent interactions, especially dispersion, between the substrate and catalytic ligand to realize C5-borylation of indoles with high reactivity and selectivity. The successful computational predictions of new ligands should be suitable for ligand design in other transition-metal catalyzed reactions.

Ru(II)-Catalyzed C-H Amination of 1,2,3-Benzotriazinones with Azide Compounds

A Ru(II)-catalyzed directed C-H amination of 1,2,3-benzotriazinones with azide compounds has been reported. The reaction has a wide substrate scope of organic azides with good results and represents a useful pathway to the construction of versatile heterocyclic amino products. In addition, the method can be used for the phthalazinones, highlighting the synthetic practicability of the strategy.

Switchable Synthesis of Tritylone Alcohols and 2-Benzoylbenzoate Esters from Spiroindane-1,3-diones

A solvent-controlled regioselective rearrangement reaction of spiroindane-1,3-diones with a leaving group has been developed. In acetonitrile solvent, the spiroindane-1,3-diones 3 were rearranged to provide tritylone alcohols, while 2-benzoylbenzoate ester derivatives were obtained if the reactions were performed in alcohols.

Regiodivergent C-H alkynylation of 2-arylthiazoles switched by RuII and PdII catalysis

Two complementary regiodivergent C-H alkynylations of 2-arylthiazoles are reported. When RuII catalysis is employed, an aryl ortho-alkynylation process is favored. The alkynylated products are gained in good yields. With the use of PdII catalysis, a thiazole C5-alkynylation process is developed, allowing for the construction of C5-alkynylated products. This strategy not only expands the methods for the functionalization of 2-arylthiazoles, but also provides new opportunities for the rapid assembly of complex molecular structures, which may have great potential in organic synthesis, medicinal chemistry, and materials science.

Ligand-Enabled ortho-Selective C-H Olefination of Tertiary Aniline Derivatives

A highly ortho-selective CAr-H olefination of tertiary anilines without a directing group was developed. This reaction tolerated various substituted arenes and olefin coupling partners, affording ortho-olefination products in moderate to good yields. Preliminary mechanistic studies showed that N-Ac-d-Ala, Ag2CO3, and BQ were the key factors for tuning the regioselectivity from para to ortho. Density functional theory was used to achieve a theoretical understanding of the ortho selectivity.

Skeletal Editing of Isatins for Heterocycle Molecular Diversity

Isatins have been widely used in the preparation of a variety of heterocyclic compounds, where the skeletal editing of isatins has shown significant advantages for the construction of diverse heterocycles. This review highlights the progress made in the last decade (2013-2023) in the skeletal editing of the isatin scaffold. A series of ring expansion reactions for the construction of quinoline skeleton, quinolone skeleton, polycyclic quinazoline skeleton, medium-sized ring skeleton, as well as a series of ring opening reactions for the generation of 2-(azoly)aniline skeleton by the cleavage of C-C bond and C-N bond are highlighted. It is hoped that this review will provide some understanding of the chemical transformations of isatins and contribute to the further realization of its molecular diversity.

Microwave-Assisted Ru(II)-Catalyzed Regioselective Methyl Acylation of 2-Arylbenzoazoles: Synthesis of Benzofuran Conjugates via C-H Activation/Annulation

An efficient Ru(II)-catalyzed C-H functionalization protocol for 2-arylbenzoazoles as the directing group and sulfoxonium ylide has been developed. Gratifyingly, concomitant annulation was observed when 3-(benzo[d]azol-2-yl) phenol was used, enabling the construction of benzofuran conjugates. Notably, the utilization of water as the solvent and an energy efficient approach makes the reaction greener, contributing to overall sustainability. This protocol exhibits excellent scalability up to the gram scale with a diverse array of substitutions. Furthermore, the mechanism was examined by ESI-MS, and photophysical studies were also performed.

Non-Directed C-H Arylation of Anisole Derivatives via Pd/S,O-Ligand Catalysis

Non-directed C-H arylation is one of the most efficient methods to synthesize biaryl compounds without the need of the prefuctionalization of starting materials, or the installment and removal of directing groups on the substrate. A direct C-H arylation of simple arenes as limiting reactants remains a challenge. Here we disclose a non-directed C-H arylation of anisole derivatives as limiting reagents with aryl iodides under mild reaction conditions. The arylated products are obtained in synthetically useful yields and the arylation of bioactive molecules is also demonstrated. Key to the success of this methodology is the use of a one-step synthesized S,O-ligand.

Ligand-Controlled Regiodivergent Alkoxycarbonylation of Trifluoromethylthiolated Internal Alkynes

Controlling the regioselectivity for the alkoxycarbonylation of unsymmetric internal alkynes is challenging. Herein, a palladium-catalyzed ligand-controlled regiodivergent alkoxycarbonylation of internal trifluoromethylthiolated alkynes was achieved. A series of α- or β-SCF3 acrylates from the same trifluoromethylthiolated alkyne were obtained with moderate to high yield and regioselectivity.

Diversity-oriented synthesis of indole-fused scaffolds and bis(indolyl)methane from tosyl-protected tryptamine

An efficient, diversity-oriented synthesis of indole-1,2-fused 1,4-benzodiazepines, tetrahydro-β-carbolines, and 2,2'-bis(indolyl)methanes was established starting from tosyl-protected tryptamine. These diverse privileged skeletons were controllably constructed by adjusting different hydride donors and Brønsted acids. A variety of indole-1,2-fused 1,4-benzodiazepines were facilely accessed using benzaldehydes bearing cyclic amines as hydride donors via a cascade N-alkylation/dehydration/[1,5]-hydride transfer/Friedel-Crafts alkylation sequence. The reaction site could be switched when benzaldehydes bearing an alkoxy moiety as hydride donors were used for the generation of tetrahydro-β-carbolines. On the other hand, the switchable synthesis of 2,2'-bis(indolyl)methanes could be achieved as well by applying p-TsOH·H2O as a catalyst. The reactions feature mild conditions, simple and practical operation, excellent efficiency and the use of EtOH as a green solvent. Using the concept of diversity-oriented, reagent-based synthesis, the inexpensive feedstock tryptamine was efficiently converted to three different types of privileged scaffolds, which facilitates rapid compound library synthesis for accelerating drug discovery.

A Practical and Regioselective Strategy for Aromatic C-H Difunctionalization via Site-Selective C-H Thianthrenation

Herein, we present a novel Catellani-type reaction that employed aryl-thianthrenium salts as aryl substrates to trigger the subsequent palladium/norbornene cooperatively catalyzed progress. This strategy can achieve site-selective C-H difunctionalization of aryl compounds without directing groups or a known initiating reagent. A series of functionalized syntheses of bioactive molecules further demonstrated the potential of this strategy.

Functional-Group-Directed Regiodivergent (3 + 2) Annulations of Electronically Distinct 1,3-Dienes and 2-Formyl Arylboronic Acids

Presented herein is a palladium-catalyzed asymmetric (3 + 2) annulation reaction between 1,3-dienes and 2-formylarylboronic acids, proceeding in a cascade vinylogous addition and Suzuki coupling process. Both electron-neutral and electron-deficient 1,3-dienes are compatible under similar catalytic conditions, and distinct regioselectivity is observed via functional-group control of 1,3-diene substrates. A collection of 1-indanols with dense functionalities is constructed stereoselectively.

Reaction engineering blocks ether cleavage for synthesizing chiral cyclic hemiacetals catalyzed by unspecific peroxygenase

Hemiacetal compounds are valuable building blocks in synthetic chemistry, but their enzymatic synthesis is limited and often hindered by the instability of hemiacetals in aqueous environments. Here, we show that this challenge can be addressed through reaction engineering by using immobilized peroxygenase from Agrocybe aegerita (AaeUPO) under neat reaction conditions, which allows for the selective C-H bond oxyfunctionalization of environmentally significant cyclic ethers to cyclic hemiacetals. A wide range of chiral cyclic hemiacetal products are prepared in >99% enantiomeric excess and 95170 turnover numbers of AaeUPO. Furthermore, by changing the reaction medium from pure organic solvent to alkaline aqueous conditions, cyclic hemiacetals are in situ transformed into lactones. Lactams are obtained under the applied conditions, albeit with low enzyme activity. These findings showcase the synthetic potential of AaeUPO and offer a practical enzymatic approach to produce chiral cyclic hemiacetals through C-H oxyfunctionalization under mild conditions.

Cu-Catalyzed Divergent Transformations of Allenylethylene Carbonates with Diboron Reagents

Divergent transformations of allenylethylene carbonates with diboron reagents catalyzed by copper are disclosed. By using CuCl/IPr·HCl as the catalyst, the allenylethylene carbonates react with B2hex2 to afford 2,4-dien-1-ols as the product in the presence of Cs2CO3 as the base, iPrOH as the additive, and 1,4-dioxane as the solvent. And they react with B2pin2 to form boronic half acids in the presence of NaOtBu as the base, water as the additive, and THF as the solvent. The reactions afford corresponding products in good stereoselectivities and yields, and further derivatizations of boronic half acids and study of the mechanism are also demonstrated.

Switchable Decarboxylation by Energy- or Electron-Transfer Photocatalysis

Kolbe dimerization and Hofer-Moest reactions are well-investigated carboxylic acid transformations, wherein new carbon-carbon and carbon-heteroatom bonds are constructed via electrochemical decarboxylation. These transformations can be switched by choosing an electrode that allows control of the reactive intermediate, such as carbon radical or carbocation. However, the requirement of a high current density diminishes the functional group compatibility with these electrochemical reactions. Here, we demonstrate the photocatalytic decarboxylative transformation of activated carboxylic acids in a switchable and functional group-compatible manner. We discovered that switching between Kolbe-type or Hofer-Moest-type reactions can be accomplished with suitable photocatalysts by controlling the reaction pathways: energy transfer (EnT) and single-electron transfer (SET). The EnT pathway promoted by an organo-photocatalyst yielded 1,2-diarylethane from arylacetic acids, whereas the ruthenium photoredox catalyst allows the construction of an ester scaffold with two arylmethyl moieties via the SET pathway. The resulting radical intermediates were coupled to olefins to realize multicomponent reactions. Consequently, four different products were selectively obtained from a simple carboxylic acid. This discovery offers new opportunities for selectively synthesizing multiple products via switchable reactions using identical substrates with minimal cost and effort.

One-Pot Manganese (I)-Catalyzed Oxidant-Controlled Divergent Functionalization of 2-Arylindazoles

The oxidant-controlled divergent synthesis of C-2' formyl 2H-indazoles and indazoloindazolediones has been developed through Mn(I)- catalyzed ortho C-H functionalization of 2H-indazoles with para-formaldehyde to afford C-2' hydroxymethylated 2H-indazoles and subsequently oxidation with varying the amount of DDQ in one-pot. By employing selectfluor as the oxidant instead of DDQ, this reaction exclusively provided indazolebenzoxazine derivatives. This strategy delivered unsymmetrical indazoloindazoledione and indazolobenzoxazine with varied functional group tolerance in moderate to good yields.

Visible-Light-Mediated Bimetal-Catalyzed meta-Alkylation of Arenes

A mild approach to the visible-light-mediated bimetal-catalyzed meta-alkylation of arenes has been accomplished. The regioselective meta-alkylation is realized by a bimetallic ruthenium-palladium system. Ruthenium acts as a catalyst for the directing effect and as a photosensitizer, while the cocatalyst palladium behaves as a catalyst for the generation of fluoroalkyl radicals. This reaction not only is suitable for two-component meta-fluoroalkylation of arenes but can also be extended to three-component reactions to achieve bifunctionalization of olefins.

Ion mobility mass spectrometry uncovers regioselectivity in the carboxylate-assisted C-H activation of palladium N-heterocyclic carbene complexes

Carboxylate-assisted Pd-catalyzed C-H bond activation constitutes a mild and versatile synthetic tool to efficiently and selectively cleave inert C-H bonds. Herein, we demonstrate a simple method to experimentally evaluate both reactivity and selectivity in such systems using mass spectrometry (MS) methods. The N-heterocyclic carbene (NHC) cations [(NHC)PdX]+, bearing as X- ligand bases commonly used to promote the C-H activation (carboxylates and bicarbonate), are generated in the gas-phase by ESI-MS. Their C-H bond activation at the N-bound groups of the NHC is then studied using Collision Induced Dissociation (CID) experiments. Ion Mobility Spectrometry (IM)-MS is exploited to identify a number of regioisomers associated with the distinctive site selective C-H activations. It is demonstrated that such C-H activation concomitant with acetic acid release occurs from a mixture of activated [(NHC-H)Pd(CH3CO2H)]+ and non-activated [(NHC)Pd(CH3CO2)]+ complexes. The identity of the X-type ligands (X = Cl-, carboxylates and bicarbonate) has a significant impact on the regioisomer branching ratio upon CID conditions. IM-MS in conjunction with a DFT mechanistic study is presented for the acetate-assisted C-H activation of the [(NHC)Pd(CH3CO2)]+ cation featuring butyl and aryl as N-donor groups.

Current Market Potential and Prospects of Copper-based Pyridine Derivatives: A Review

Nicotine, minodronic acid, nicotinamide (niacin), zolpidem, zolimidine, and other pyridine-based chemicals play vital roles in medicine and biology. Pyridinecontaining drugs are widely available on the market to treat a wide range of human ailments. As a result of these advances, pyridine research is continually expanding, and there are now higher expectations for how it may aid in the treatment of numerous ailments. This evaluation incorporates data acquired from sources, like PubMed, to provide a thorough summary of the approved drugs and bioactivity data for compounds containing pyridine. Most of the reactions discussed in this article will provide readers with a deeper understanding of various pyridine-related examples, which is necessary for the creation of copper catalysis-based synthetic processes that are more accessible, secure, environmentally friendly, and practical, and that also have higher accuracy and selectivity. This paper also discusses significant innovations in the multi-component copper-catalyzed synthesis of N-heterocycles (pyridine), with the aim of developing precise, cost-effective, and environmentally friendly oxygenation and oxidation synthetic methods for the future synthesis of additional novel pyridine base analogs. Therefore, the review article will serve as a novel platform for researchers investigating copperbased pyridine compounds.

Rh(III)-catalyzed selective C2 C-H acyloxylation of indoles

Herein, we present the first highly regio- and chemoselective C2 C-H acyloxylation of indole under rhodium catalysis and an N-quinolinyl auxiliary. This strategy accommodates a wide range of indoles and structurally diverse carboxylic acids with good reaction efficiencies to yield functionalized indoles. The utility of this logic was demonstrated by the concise synthesis of the functionalized 2-oxindole derivatives. Preliminary mechanistic studies indicate that catalyst turnover of RhIII-RhIV/V-RhII/III-RhIII might be involved in this catalytic C-H transformation.

Enantioselective and Regiodivergent Synthesis of Dihydro-1,2-oxazines from Triene-Carbamates via Chiral Phosphoric Acid-Catalysis

Conjugated trienes are fascinating building blocks for the rapid construction of complex polycyclic compounds. However, limited success has been achieved due to the challenging regioselectivity control. Herein, we report an enantio- and diastereoselective process allowing to regioselectively control the functionalization of NH-triene-carbamates. Synthesis of chiral cis-3,6-dihydro-2H-1,2-oxazines is achieved by a chiral phosphoric acid catalyzed Nitroso-Diels-Alder cycloaddition involving [(1E,3E,5E)-hexa-1,3,5-trien-1-yl]carbamates. Moreover, modular access to three different regioisomers with excellent diastereoselectivities and high to excellent enantioselectivities is obtained by a careful choice of the reaction conditions. A computational study reveals that the regioselectivity is influenced by the steric demand of the substituents at the 6-position of the triene, as well as noncovalent interactions between the two cycloaddition partners. Utility of each regioisomeric cycloadduct is highlighted by a variety of synthetic transformations.

A Simple Access to γ- and ε-Keto Arenes via Enzymatic Divergent C─H Bond Oxyfunctionalization

Performing divergent C─H bond functionalization on molecules with multiple reaction sites is a significant challenge in organic chemistry. Biocatalytic oxyfunctionalization reactions of these compounds to the corresponding ketones/aldehydes are typically hindered by selectivity issues. To address these challenges, the catalytic performance of oxidoreductases is explored. The results show that combining the peroxygenase-catalyzed propargylic C─H bond oxidation with the Old Yellow Enzyme-catalyzed reduction of conjugated C─C triple bonds in one-pot enables the regio- and chemoselective oxyfunctionalization of sp3 C─H bonds that are distant from benzylic sites. This enzymatic approach yielded a variety of γ-keto arenes with diverse structural and electronic properties in yields of up to 99% and regioselectivity of 100%, which are difficult to achieve using other chemocatalysis and enzymes. By adjusting the C─C triple bond, the carbonyl group's position can be further tuned to yield ε-keto arenes. This enzymatic approach can be combined with other biocatalysts to establish new synthetic pathways for accessing various challenging divergent C─H bond functionalization reactions.

Regioselectivity Switch between Enantioselective 1,2- and 1,4-Addition of Allyl Aryl Ketones with 2,3-Dioxopyrrolidines

A vinylogous addition reaction of allyl aryl ketones with good yields and excellent regioselectivity catalyzed by squaramide catalysts has been developed. A series of chiral tertiary alcohols and bicyclic pyrrolidones could be synthesized in good to excellent yields, enantioselectivities, and diaseteroselectivities. Both experimental results and DFT calculations indicate that 1,2-addition reaction is favorable when the reaction is employed at a lower temperature, while the 1,4-addition/cyclization pathway is favorable when the reaction is employed at a higher temperature. Furthermore, the formation of compound 4 can potentially arise from either the 1,4-addition/cyclization pathway or retro-aldol reaction of compound 3, followed by subsequent 1,4-addition/cyclization.

Merging Visible Light Photocatalysis and P(III)-Directed C-H Activation by a Single Catalyst: Modular Assembly of P-Alkyne Hybrid Ligands

Metal-catalyzed C-H activation strategies provide an efficient approach for synthesis by minimizing atom, step, and redox economy. Developing milder, greener, and more effective protocols for these strategies is always highly desirable to the scientific community. In this study, the utilization of a single rhodium complex enabled the visible-light-induced late-stage C-H activation of biaryl-type phosphines with alkynyl bromides, employing inherent phosphorus atoms as directing groups. This chemistry combines P(III)-directed C-H activation with visible light photocatalysis, under exogenous photosensitizer-free conditions, offering a unique platform for ligand design and preparation. Furthermore, this study also explores the asymmetric catalysis and coordination chemistry of the resulting P-alkyne hybrid ligands with specific transition metals. Experimental results and density functional theory calculations demonstrate the mechanistic intricacies of this transformation.

Rhodaelectro-Catalyzed Decarboxylative Cross-Dehydrogenative Coupling of Indole-3-carboxylic Acids and Olefins via Weakly Coordinating Carboxyl Groups

A rhodaelectro-catalyzed C2-H selectively decarboxylative alkenylation of 3-carboxy-1H-indoles employing electricity as the traceless terminal oxidant has been accomplished. The weakly coordinating carboxyl group serves as the traceless directing groups. External oxidant-free in an undivided cell with constant current in aqueous solution ensures the decarboxylative C-H alkenylation to be viable and sustainable.

Transition-Metal-Catalyzed Dehydrogenative (3 + 2) Annulation of Aromatic Compounds: Synthesis of Indenes and Indanes via Dual Functionalization of Benzylic and ortho C-H Bonds

Intermolecular (3 + 2) annulation emerges as a potent approach for constructing 5-membered carbocycles through the fusion of two distinct components. This synopsis encapsulates recent strides in the realm of transition-metal-catalyzed dehydrogenative (3 + 2) annulation of aromatic hydrocarbons, achieved through the dual functionalization of benzylic and ortho C-H bonds. Encompassing three pivotal strategies, namely, (i) C-H bond activation, (ii) benzylic oxidation, and (iii) π-coordination activation, this review offers an overview of the field's recent developments.

Iridium(III)-Catalyzed Intermolecular C(sp3 )-H Amidation for the Synthesis of Chiral 1,2-Diamines

Chiral 1,2-diamines are privileged scaffolds among bioactive natural products, active pharmaceutical ingredients, ligands for transition-metal-based asymmetric catalysis and organocatalysts. Despite this interest, the construction of chiral 1,2-diamine motifs still remains a challenge. To address this, an iridium(III)-catalyzed intermolecular C(sp3 )-H amidation reaction was developed. This method relies on the design of a new, cheap and cleavable exo-protecting/directing group derived from camphorsulfonic acid, which is directly installed from easily accessible precursors, and furnishes scalemic free 1,2-diamines upon cleavage of both nitrogen substituents. It was found applicable to both α-secondary and α-tertiary-1,2-diamines, for which a two-step protocol involving intermolecular olefin hydroamination and C(sp3 )-H amidation was developed. Kinetic and computational studies provided insights into the observed reactivity difference between pairs of diastereoisomeric substrates.

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.

Palladium-Catalyzed Regiodivergent C-H Olefination of Imidazo[1,2a]pyridine Carboxamide and Unactivated Alkenes

Despite remarkable successes in linear and branched vinyl (hetero) arene synthesis, regiodivergent C-H olefination with a single catalytic system has remained underdeveloped. Overcoming this limitation, a Pd/MPAA-catalyzed regiodivergent C-H olefination of imidazo[1,2a] pyridine carboxamides with unactivated terminal alkenes to generate branched and linear olefinated products depending upon the electronic nature of alkenes is reported herein. Moreover, this protocol can be applied for C-H deuteriation of the corresponding heteroarenes with D2 O as deuterium source. Preliminary experimental studies combined with computational investigations (DFT studies) suggest that regiodivergent olefination can be controlled by olefin insertion and β-hydride elimination steps.

B(C6F5)3-mediated direct intramolecular C7-alkenylation of N-propargylindoles

B(C6F5)3-mediated direct C7-alkenylation of N-propargylindoles without directing groups was developed. This reaction proceeds via the π-activation of the alkynyl group with B(C6F5)3/Friedel-Crafts alkenylation/proton transfer reaction sequence. Interestingly, C7-alkenylation products could further convert into the fused indoles by deprotonation and finally polyaromatic N-heterocycles by the hydride abstraction.

Cobalt(III)-Catalyzed Directed C-7 Selective C-H Alkynylation of Indolines with Bromoalkynes

A cobalt(III)-catalyzed directed C-7 alkynylation of indolines with easily accessible bromoalkynes has been developed. The reaction has a broad substrate scope with excellent yields and represents a powerful route to the synthesis of 7-alkynyl-substituted indolines. In addition, the reaction can be extended to the coupling of N-aryl 7-azaindoles, highlighting the synthetic practicability of the strategy.

Catalyst-controlled regiodivergent C-H bond alkenylation of 2-pyridylthiophenes

A novel and effective Rh^III- and Pd^II-controlled switchable C-H alkenylation of 2-pyridylthiophenes with alkenes is realized. The alkenylation reactions proceeded smoothly in a highly regio- and stereo-selective manner to afford a broad range of C3- and C5-alkenylated products. Depending on the catalyst employed, the reactions involve two typical approaches: C3-alkenylation via chelation-assisted rhodation and C5-alkenylation via electrophilic palladation. This regiodivergent synthetic protocol was successfully applied for the straightforward building of π-conjugated difunctionalized 2-pyridylthiophenes, which may show great potential in organic electronic materials.

Thiochromane Formation via Visible-Light-Mediated Intramolecular δ-C(sp3)-H Bond Arylation of Sulfonamides

Visible-light-mediated intramolecular site-selective δ-C(sp³)-H bond arylation of aliphatic trifluoromethanesulfonamides was developed. The reaction proceeds through a radical cascade, including the generation of a sulfonamidyl radical, which triggers a 1,5-hydrogen atom transfer, affording a δ-C-centered radical, which finally cyclized onto a neighboring thiopolyfluoroaryl moiety to deliver a range of synthetically useful thiochromanes. The cyclization process occurs through two distinct pathways depending upon the nature of the substituent X ortho to the native C-S bond.

Iridium catalysed C2 site-selective methylation of indoles using a pivaloyl directing group through weak chelation-assistance

Here we present an iridium catalysed C2-selective methylation of indoles using methyltrifluoroborate as a source of methyl group. The iridium catalyst selectively discriminates the indole C2 and C4 C-H bonds by coordination with a pivaloyl directing group.

Modulation of metal species as control point for Ni-catalyzed stereodivergent semihydrogenation of alkynes with water

A base-assisted metal species modulation mechanism enables Ni-catalyzed stereodivergent transfer semihydrogenation of alkynes with water, delivering both olefinic isomers smoothly using cheap and nontoxic catalysts and additives. Different from most precedents, in which E-alkenes derive from the isomerization of Z-alkene products, the isomers were formed in orthogonal catalytic pathways. Mechanistic studies suggest base as a key early element in modulation of the reaction pathways: by adding different bases, nickel species with disparate valence states could be accessed to initiate two catalytic cycles toward different stereoisomers. The practicability of the method is showcased with nearly 70 examples, including internal and terminal triple bonds, enynes and diynes, affording semi-hydrogenated products in high yields and selectivity.

Unlocking Regiodivergence in PdII- and RhIII-Mediated Site-Selective C-H Bond Alkynylation of Imidazopyridines

An efficient Pd^II- and Rh^III-controlled site-selective C-H bond alkynylation of imidazopyridines using (bromoethynyl)triisopropylsilane is disclosed. The divergent methodology allows straightforward access to a wide range of products alkynylated at the C3 and ortho positions. This strategy is suggestive of a practical platform that can be suitable for late-stage diversification and may assist in the design of more selective and complementary catalytic systems.

Ru3 (CO)12 -Catalyzed Modular Assembly of Hemilabile Ligands by C-H Activation of Phosphines with Isocyanates

Hemilabile ligands have been applied extensively in transition metal catalysis, but preparations of these molecules typically require multistep synthesis. Here, modular assembly of diverse phosphine-amide ligands, including related axially chiral compounds, is first reported through ruthenium-catalyzed C-H activation of phosphines with isocyanate directed by phosphorus(III) atoms. High reactivity and regioselectivity can be obtained by using a Ru₃ (CO)₁₂ catalyst with a mono-N-protected amino acid ligand. This transformation significantly expands the pool of phosphine-amide ligands, some of which have shown excellent efficiency for asymmetric catalysis. More broadly, the discovery constitutes a proof of principle for facile construction of hemilabile ligands directly from the parent monodentate phosphines by C-H activation with ideal atom, step and redox economy. Several dinuclear ruthenium complexes were characterized by single-crystal X-ray diffraction analysis revealing the key mechanistic features of this transformation.

Iridium-Catalyzed ortho-Selective Borylation of Aromatic Amides Enabled by 5-Trifluoromethylated Bipyridine Ligands

Iridium-catalyzed borylations of aromatic C-H bonds are highly attractive transformations because of the diversification possibilities offered by the resulting boronates. These transformations are best carried out using bidentate bipyridine or phenanthroline ligands, and tend to be governed by steric factors, therefore resulting in the competitive functionalization of meta and/or para positions. We have now discovered that a subtle change in the bipyridine ligand, namely, the introduction of a CF₃ substituent at position 5, enables a complete change of regioselectivity in the borylation of aromatic amides, allowing the synthesis of a wide variety of ortho-borylated derivatives. Importantly, thorough computational studies suggest that the exquisite regio- and chemoselectivity stems from unusual outer-sphere interactions between the amide group of the substrate and the CF₃ -substituted aryl ring of the bipyridine ligand.

Charge-controlled Pd catalysis enables the meta-C–H activation and olefination of arenes

The regioselective C-H activation of arenes remains one of the most promising techniques for accessing highly important functionalized motifs. Such functionalizations can generally be achieved through directed and non-directed processes. The directed approach requires a covalently attached directing group (DG) on the substrate to induce reactivity and selectivity and therefore intrinsically leaves a functional group at the point of attachment within the molecule, even after the tailored DG has been removed. Conversely, non-directed methods typically suffer from regioselectivity issues, especially for unbiased substrates. Herein, we report a unique approach that employs weak charge-charge and charge-dipole interactions to enable the meta-selective activation and olefination of arenes to address these challenges in Pd catalysis. The charged moiety can easily be converted to uncharged simple arenes by hydrogenation or cross-coupling. In-depth mechanistic studies prove that the charge is responsible for the observed selectivity. We expect our studies to be generalizable and thereby enable further regioselective transformations.