Development of Chiral Ligands for the Transition-Metal-Catalyzed Enantioselective Silylation and Borylation of C-H Bonds

Ether-Directed Enantioselective C(sp2)-H Borylation for the Synthesis of Axially Chiral Biaryls

We report an ether-directed enantioselective C(sp2)-H borylation catalyzed by a chiral bidentate boryl ligand (CBL)/iridium system for constructing axially chiral biaryls. This method delivered diverse chiral biaryls with good to high enantioselectivities, accommodating varied electronic and steric substituents on the aryl rings. Gram-scale synthesis and downstream transformations of the C-B bond underscored its practicality.

Enantioselective α-C(sp3)-H Borylation of Masked Primary Alcohols Enabled by Iridium Catalysis

Functional group-directed site- and enantioselective C(sp3)-H functionalization of alcohols or masked alcohols represents a formidable challenge. We herein report the first example of iridium-catalyzed asymmetric α-C(sp3)-H borylation of primary alcohol-derived carbamates by the judicious choice of directing groups. A variety of chiral borylated carbamates were obtained with good to high enantioselectivities. We also demonstrated the synthetic utility by taking advantage of the highly transformable feature of C-B bonds and the leaving ability of carbamates.

Asymmetric Synthesis of Chiral Calix[4]arenes with Both Inherent and Axial Chirality via Cobalt-Catalyzed Enantioselective Intermolecular C-H Annulation

Inherently chiral calixarenes have garnered significant attention due to their distinctive properties, yet the development of efficient catalytic asymmetric synthesis methods remains a critical challenge. Herein, we report the asymmetric synthesis of calix[4]arenes featuring inherent or both inherent and axial chirality via a cobalt-catalyzed C-H activation/annulation strategy in high yield with excellent enantio- and diastereoselectivity (up to >99 % ee and >20 : 1 dr). Electrooxidation was also suitable for this transformation to obviate the sacrificial metal oxidants, underscoring the environmentally friendly potential of this approach. A key octahedral cobaltacycle intermediate was synthesized and characterized, providing valuable insights into the mode of enantio- and diastereocontrol of this protocol. Noteworthy photoluminescence quantum yields of up to 0.94 were measured, underscoring the potential of these compounds in the domain of organic fluorescent materials.

Enantioselective 1,4-Borylamination via Copper-Catalyzed Cascade Hydroborylation and Hydroamination of Arylidenecyclopropanes

Compounds bearing both boryl and amino groups at distal positions are invaluable synthons for synthesizing pharmaceuticals, drug candidates, and natural products, but their catalytic enantioselective synthesis remains rarely explored. We report the first enantioselective 1,4-borylamination reaction through a copper-catalyzed cascade hydroborylation and hydroamination of arylidenecyclopropanes. This reaction combines four readily available components in a highly chemo-, site-, and enantioselective fashion (>20:1 r.r. and up to 99% ee), yielding a diverse array of synthetically valuable enantioenriched 4-amino alkylboronates. The versatile utility of these products is highlighted by their diverse transformations and wide applications in pharmaceutical synthesis and drug discovery. Preliminary mechanistic studies were conducted to elucidate the operative reaction pathway, intermediates, and origins of its high chemo- and site-selectivity.

Catalytic Asymmetric Construction of C- and Si-Stereogenic Silacyclopentanes via Hydrosilylation of Arylmethylenecyclopropanes

Silacycles have exhibited significant potential for application in the fields of medicinal chemistry, agrochemistry, and materials science. Accordingly, the development of effective methods for synthesizing these compounds has attracted increasing attention. Here, we report an efficient Cu-catalyzed enantioselective hydrosilylation of arylmethylenecyclopropanes with hydrosilanes, that allows the rapid assembly of various enantioenriched carbon- and silicon-stereogenic silacyclopentanes in good yields with excellent enantioselectivities and diastereoselectivities under mild conditions. Further stereospecific transformation of the Si-H bond on the chiral silicon center expands the diversity of these C- and Si-stereogenic silacyclopentanes.

Asymmetric Dearomatization of Indoles through Cobalt-Catalyzed Enantioselective C-H Functionalization Enabled by Photocatalysis

Photocatalysis holds a pivotal position in modern organic synthesis, capable of inducing novel reactivities under mild and environmentally friendly reaction conditions. However, the merger of photocatalysis and transition-metal-catalyzed asymmetric C-H activation as an efficient and sustainable method for the construction of chiral molecules remains elusive and challenging. Herein, we develop a cobalt-catalyzed enantioselective C-H activation reaction enabled by visible-light photoredox catalysis, providing a synergistic catalytic strategy for the asymmetric dearomatization of indoles with high levels of enantioselectivity (96 % to >99 % ee). Mechanistic studies indicate that the excited photocatalyst was quenched by divalent cobalt species in the presence of Salox ligand, leading to the formation of catalytically active chiral Co(III) complex. Moreover, stoichiometric reactions of cobaltacycle intermediate with indole suggest that the irradiation of visible light also play a critical role in the dearomatization step.

Visible-Light Mediated Nickel-Catalyzed Asymmetric Difunctionalizations of Alkenes

Difunctionalizations of alkenes represent one of the most straightforward protocols to build molecular complexity due to the simultaneous construction of two vicinal bonds cross π-bond of alkenes. It is extremely attractive yet challenging to control the stereochemistry outcome of this event. Over the past years, visible-light and Ni-catalyzed asymmetric difunctionalizations of alkenes provide an environmental benign and promising solution for the construction of saturated carbon centers with the control of regio- and enantioselectivity. In this Concept, the initiative and progress of regio- and enantioselective difunctionalizations of alkenes enabled by visible-light and nickel catalysis has been summarized. Moreover, further efforts and directions for the development of visible-light mediated Ni-catalyzed asymmetric difunctionalizations of alkenes has been discussed.

Cu(II)-Catalyzed Hydroboration Reactions of 1,1-Disubstituted α,β-Unsaturated Ketones, Esters, and Amides in Pure Water

Here, a Cu2(OH)2CO3-catalyzed hydroboration reaction of 1,1-disubstituted α,β-unsaturated compounds has been developed. The reaction was carried out using water as a solvent at room temperature except for N-monosubstituted α,β-unsaturated amides. This method is applicable to diverse 1,1-disubstituted α,β-unsaturated ketones, esters, and amides, showing excellent reactivity (up to 98% yield). Gram-scale experiments and functional group transformations further demonstrated the practicality of this method.

Synthesis of chiral Cu(II) complexes from pro-chiral Schiff base ligand and investigation of their catalytic activity in the asymmetric synthesis of 1,2,3-triazoles

A pro-chiral Schiff base ligand (HL) was synthesized by the reaction of 2-amino-2-ethyl-1,3-propanediol and pyridine-2-carbaldehyde in methanol. The reaction of HL with CuCl2·2H2O and CuBr2 in methanol gave neutral mononuclear Cu(II) complexes with general formula of [Cu(HL)Cl2] (1) and [Cu(HL)Br2] (2), respectively. By slow evaporation of the methanolic solutions of 1 and 2, their enantiomers were isolated in crystalline format. The formation of pure chiral crystals in the racemic mixture was amply authenticated by single crystal X-ray analysis, which indicated that S-[Cu(HL)Cl2], R-[Cu(HL)Cl2], and S-[Cu(HL)Br2] are crystallized in chiral P212121 space group of orthorhombic system. Preferential crystallization was used to isolate the R and S enantiomers as single crystals and the isolated compounds were also studied by CD analysis. Structural studies indicated that the origin of the chirality in these compounds is related to the coordination mode of the employed pro-chiral ligand (HL) because one of its carbon atoms has been converted to a chiral center in the synthesized complexes. Subsequently, these complexes were used in click synthesis of a β-hydroxy-1,2,3-triazole and the results of catalytic studies indicated that 1 and 2 can act as enantioselective catalysts for the asymmetric synthesis of β-hydroxy-1,2,3-triazole product under mild condition. This study illustrates the significant capacity of the use of pro-chiral ligands in preparing chiral catalysts based on complexes which can also be considered as an effective approach to cheap chiral catalysts from achiral reagents.

Enantioselective and Regiodivergent Synthesis of Propargyl- and Allenylsilanes through Catalytic Propargylic C-H Deprotonation

We report a highly enantioselective intermolecular C-H bond silylation catalyzed by a phosphoramidite-ligated iridium catalyst. Under reagent-controlled protocols, propargylsilanes resulting from C(sp3)-H functionalization, as well the regioisomeric and synthetically versatile allenylsilanes, could be obtained with excellent levels of enantioselectivity and good to excellent control of propargyl/allenyl selectivity. In the case of unsymmetrical dialkyl acetylenes, good to excellent selectivity for functionalization at the less-hindered site was also observed. A variety of electrophilic silyl sources (R3SiOTf and R3SiNTf2), either commercial or in situ-generated, were used as the silylation reagents, and a broad range of simple and functionalized alkynes, including aryl alkyl acetylenes, dialkyl acetylenes, 1,3-enynes, and drug derivatives were successfully employed as substrates. Detailed mechanistic experiments and DFT calculations suggest that an η3-propargyl/allenyl Ir intermediate is generated upon π-complexation-assisted deprotonation and undergoes outer-sphere attack by the electrophilic silylating reagent to give propargylic silanes, with the latter step identified as the enantiodetermining step.

Potential Application Prospects of Biomolecule-Modified Two-Dimensional Chiral Nanomaterials in Biomedicine

Chirality, one of the most fundamental properties of natural molecules, plays a significant role in biochemical reactions. Nanomaterials with chiral characteristics have superior properties, such as catalytic properties, optoelectronic properties, and photothermal properties, which have significant potential for specific applications in nanomedicine. Biomolecular modifications such as nucleic acids, peptides, proteins, and polysaccharides are sources of chirality for nanomaterials with great potential for application in addition to intrinsic chirality, artificial macromolecules, and metals. Two-dimensional (2D) nanomaterials, as opposed to other dimensions, due to proper surface area, extensive modification sites, drug loading potential, and simplicity of preparation, are prepared and utilized in diagnostic applications, drug delivery research, and tumor therapy. Current advanced studies on 2D chiral nanomaterials for biomedicine are focused on novel chiral development, structural control, and materials sustainability applications. However, despite the advances in biomedical research, chiral 2D nanomaterials still confront challenges such as the difficulty of synthesis, quality control, batch preparation, chiral stability, and chiral recognition and selectivity. This review aims to provide a comprehensive overview of the origins, synthesis, applications, and challenges of 2D chiral nanomaterials with biomolecules as cargo and chiral modifications and highlight their potential roles in biomedicine.

Trialkoxysilane-Induced Iridium-Catalyzed para-Selective C-H Bond Borylation of Arenes

An ideal approach for the construction of aryl boron compounds is to selectively replace a C-H bond in arenes with a C-B bond, and controlling regioselectivity is one of the most challenging aspects of these transformations. Herein, we report an iridium-catalyzed trialkoxysilane protecting group-assisted regioselective C-H borylation of arenes, including derivatives of benzaldehydes, acetophenones, benzoic acids, benzyl alcohols, phenols, aryl silanes, benzyl silanes, and multi-functionalized aromatic rings are all well tolerated and gave the para -selective C-H borylation products in a short time without the requirement of inert gases atmosphere. The site-selective C-H borylation can be adjustable by installing the developed trialkoxysilane protecting group on different functional groups on one aromatic ring. Importantly, the preparation process of the trialkoxychlorosilane is efficient and scalable. Mechanistic and computational studies reveal that the steric hindrance of the trialkoxysilane protecting group plays a key role in dictating the para-selectivity.

Atroposelective Chan-Evans-Lam Amination

The synthetic control of atropoisomerism along C-N bonds is a major challenge, and methods that allow C-N atroposelective bond formation are rare. This is a problem because each atropoisomer can feature starkly differentiated biological properties. Yet, among the three most practical and applicable classical amination methods available: 1) the Cu-catalyzed Ullmann-Goldberg reaction, 2) the Pd-catalyzed Buchwald-Hartwig reaction, and 3) the Cu-catalyzed Chan-Evans-Lam reaction, none has truly been rendered atroposelective at the newly formed C-N bond. The first ever Chan-Evans-Lam atroposelective amination is herein described with a simple copper catalyst and newly designed PyrOx chiral ligand. This method should find important applications in asymmetric synthesis, in particular for medicinal chemistry.

Enantioselective Desymmetrization of Trifluoromethylated Tertiary Benzhydrols via Hydrogen-Acceptor-Free Ir-Catalyzed Dehydrogenative C-H Silylation: Decisive Role of the Trifluoromethyl Group

Although the trifluoromethyl (CF3) group is one of the most important fluorinated groups owing to its significant ability to modulate pharmacological properties, constructing trifluoromethylated stereogenic centers in an enantioselective manner has been a formidable challenge. Herein, we report the development of the enantioselective desymmetrization of trifluoromethylated benzhydrols via intramolecular dehydrogenative silylation using Ir catalysts with chiral pyridine-oxazoline (PyOX) ligands. The produced benzoxasilol was transformed into several unsymmetrical benzhydrols via iododesilylation and subsequent transition-metal-catalyzed cross-coupling reactions. Moreover, the same Ir catalyst system was used for the kinetic resolution of unsymmetrical trifluoromethylated benzhydrols.

Catalytic Enantioselective Primary C-H Borylation for Acyclic All-Carbon Quaternary Stereocenters

Creating a perfect catalyst to operate enzyme-like chiral recognition has been a long-sought aim. A challenging example in this context is constructing acyclic all-carbon quaternary stereogenic centers by transition metal-catalyzed enantioselective C-H activation. We now report highly enantioselective iridium-catalyzed primary C-H borylation of α-all-carbon substituted 2,2-dimethyl amides enabled by a tailor-made chiral bidentate boryl ligand (CBL). The success of the current transformation is attributed to the CBL/iridium catalyst, which has a confined chiral pocket. This protocol provides a diverse array of acyclic all-carbon quaternary stereocenters with excellent enantiocontrol and distinct structural features. Computational study reveals that steric hindrance of CBL could regulate the type of dominant orbital interaction between the catalyst and substrate, which is crucial to conferring high chiral induction.

Rhodium-Catalyzed Enantioselective Formal [4+1] Cyclization of Benzyl Alcohols and Benzaldimines: Facile Access to Silicon-Stereogenic Heterocycles

The carbon-to-silicon switch in formation of bioactive sila-heterocycles with a silicon-stereogenic center has garnered significant interest in drug discovery. However, metal-catalyzed synthesis of such scaffolds is still in its infancy. Herein, a rhodium-catalyzed enantioselective formal [4+1] cyclization of benzyl alcohols and benzaldimines has been realized by enantioselective difunctionalization of a secondary silane reagent, affording chiral-at-silicon cyclic silyl ethers and sila-isoindolines, respectively. Mechanistic studies reveal a dual role of the rhodium-hydride catalyst. The coupling system proceeds via rhodium-catalyzed enantio-determining dehydrogenative OH silylation of the benzyl alcohol or hydrosilylation of the imine to give an enantioenriched silyl ether or silazane intermediate, respectively. The same rhodium catalyst also enables subsequent intramolecular cyclative C-H silylation directed by the pendent Si-H group. Experimental and DFT studies have been conducted to explore the mechanism of the OH bond silylation of benzyl alcohol, where the Si-O reductive elimination from a Rh(III) hydride intermediate has been established as the enantiodetermining step.

Continuous-Flow Enantioselective Hydroacylations under Heterogeneous Chiral Rhodium Catalysts

Transition metal-catalyzed enantioselective C-H bond functionalizations have become efficient methods for the synthesis of complex optically active molecules. Heterogeneous catalysts for this chemistry remain largely unexplored despite the advantages they offer in terms of ease of separation and reuse of catalysts. Herein, we report the development of heterogeneous chiral Rh catalysts for continuous-flow enantioselective hydroacylations. Heterogeneous catalysts could be prepared simply by mixing supports and Rh complexes. The prepared catalysts exhibited excellent activity and enantioselectivity affording optically active ketones in quantitative yields with 99 % ee's. Under the optimized reaction conditions, a turnover number >300 was achieved without the leaching of Rh species. The catalysts exhibited a wide substrate scope and in sequential-flow reactions with other heterogeneous catalysts, the syntheses of biologically active molecules and functional materials were demonstrated.

Aryl Chloride-Directed Enantioselective C(sp2)-H Borylation Enabled by Iridium Catalysis

We herein report the iridium-catalyzed enantioselective C-H borylation of aryl chlorides. A variety of prochiral biaryl compounds could be well-tolerated, affording a vast array of axially chiral biaryls with high enantioselectivities. The current method exhibits a high turnover number (TON) of 7000, which represents the highest in functional-group-directed asymmetric C-H activation. The high TON was attributed to a weak catalyst-substrate interaction that was caused by mismatched chirality between catalyst and substrate. We also demonstrated the synthetic application of the current method by C-B, ortho-C-H, and C-Cl bond functionalization, including programmed Suzuki-Miyaura coupling for the synthesis of axially chiral polyarenes.

Palladium-Catalyzed Modular Assembly of P-Stereogenic and Axially Chiral Phosphinooxazoles (PHOX) Ligands by C-P Bond Cleavage/Intermolecular C(sp2)-H Bond Functionalization

Chiral P,N-ligands are of great interest and importance in the fields of metal-catalyzed enantioselective transformations and have found numerous applications spanning drug and polymer synthesis. Here, modular assembly of diverse P-stereogenic and axially chiral phosphinooxazoles ligands is achieved through palladium-catalyzed asymmetric cleavage of C-P bond/intermolecular C-H bond functionalization in high atroposelectivities and diastereoselectivities of up to >99% ee and >25:1 dr. This protocol features broad substrate scope and provides an avenue for facile construction of new P-stereogenic and axially chiral phosphinooxazoles ligands directly from the phosphonium salts and benzoxazoles/benzothiazoles. Evaluation of the synthesized P-stereogenic and axially chiral phosphinooxazoles ligands in two model catalytic asymmetric reactions illustrates the potential of our strategy to access valuable chiral molecules.

Desulfurative Borylation of Small Molecules, Peptides, and Proteins

We introduce a direct conversion of alkyl thiols into boronic acids, facilitated by a water-soluble phosphine, 1,3,5-triaza-7-phosphaadamantane (PTA), in conjunction with tetrahydroxydiboron (B2(OH)4), acting as both a radical initiator and a boron source. This desulfurative borylation reaction has been successfully applied to various substrates, including cysteine residues in oligopeptides and small proteins, primary alkyl thiols found in pharmaceutical compounds, disulfides, and selenocysteine. Optimization of reaction conditions was undertaken to reduce the formation of unwanted reactions, such as the reduction of alanyl or other primary radicals, and to prevent deleterious reactions between the phosphine and N-terminal amine that lead to methylene adducts by utilizing a buffer containing glycine-glycine (GG) dipeptide. The developed method is characterized by its operational simplicity and robustness. Moreover, its compatibility with various functional groups present in peptides and proteins makes it a promising tool for late-stage functionalization, extending its potential application across a broad spectrum of chemical and biological targets.

Metal-free C-H Borylation and Hydroboration of Indoles

The C-H borylation and hydroboration reactions have emerged as promising synthetic tools to construct organoboron compounds. Organoboron compounds of N-heterocycles, particularly indole derivatives, have found widespread application in a variety of fields. As a result, considerable advancement in the area of C-H borylation and hydroboration reactions of indoles was observed in the last few decades. Among the various synthetic methods applied, the metal-free approach has received special attention. This mini-review discusses the recent progress in the area of C-H borylation and hydroboration reactions of indoles under metal-free conditions, their scope, and brief mechanistic studies.

Atroposelective Ir-Catalyzed C-H Borylation of Phthalazine Heterobiaryls

The atroposelective iridium-catalyzed borylation of menthyloxy-substituted phthalazine heterobiaryls with diborons is reported. Utilizing [Ir(OMe)(COD)]2/2-aminopyridine as a rarely used efficient catalyst system, the heterobiaryls were selectively borylated in the 2-position of the carbocycle, exclusively yielding only one of the atropisomers, depending on the substitution of the phthalazine with (+)-menthyl or (-)-menthyl moieties. Exemplary further functionalization of a borylated atropisomer demonstrated that nickel-catalyzed Suzuki-Miyaura cross-coupling with an aryl halide was able to provide stereoretention to a certain degree (up to 75% de).

Axially chiral styrene-based organocatalysts and their application in asymmetric cascade Michael/cyclization reaction

An axially chiral styrene-based organocatalyst, featuring a combination of axially chiral styrene-based structure and a pyrrole ring, has been designed and synthesized. This catalyst demonstrates remarkable capabilities in producing a wide range of densely substituted spirooxindoles that feature an alkyne-substituted quaternary stereogenic center. These spirooxindoles are generated through mild cascade Michael/cyclization reactions, resulting in high conversion rates and exceptional enantioselectivity. Our catalytic model, based on experiments, X-ray structure analysis and DFT calculations suggests that chiral matched π-π interactions and multiple H-bonds between the organocatalyst and substrates play significant roles in controlling the stereoselectivity of the reaction.

Chiral PSiSi-Ligand Enabled Iridium-Catalyzed Atroposelective Intermolecular C-H Silylation

Catalytic enantioselective intermolecular C-H silylation offers an efficient approach for the rapid construction of chiral organosilicon compounds, but remains a significant challenge. Herein, a new type of chiral silyl ligand is developed, which enables the first iridium-catalyzed atroposelective intermolecular C-H silylation reaction of 2-arylisoquinolines. This protocol features mild reaction conditions, high atom economy, and remarkable yield with excellent stereoselectivity (up to 99 % yield, 99 % ee), delivering enantioenriched axially chiral silane platform molecules with facile convertibility. Key to the success of this unprecedented transformation relies on a novel chiral PSiSi-ligand, which facilitates the intermolecular C-H silylation process with perfect chem-, regio- and stereo-control via a multi-coordinated silyl iridium complex.

Rhodium-Catalyzed Asymmetric C-H Functionalization Reactions

This review summarizes the advancements in rhodium-catalyzed asymmetric C-H functionalization reactions during the last two decades. Parallel to the rapidly developed palladium catalysis, rhodium catalysis has attracted extensive attention because of its unique reactivity and selectivity in asymmetric C-H functionalization reactions. In recent years, Rh-catalyzed asymmetric C-H functionalization reactions have been significantly developed in many respects, including catalyst design, reaction development, mechanistic investigation, and application in the synthesis of complex functional molecules. This review presents an explicit outline of catalysts and ligands, mechanism, the scope of coupling reagents, and applications.

Simple Ether-Directed Enantioselective C(sp3 )-H Borylation of Cyclopropanes Enabled by Iridium Catalysis

Reported here is an efficient and simple ether-directed iridium-catalyzed enantioselective C(sp³ )-H borylation of cyclopropanes. Various functional groups were well-tolerated, affording a vast array of chiral cyclopropanes with high enantioselectivities. We also demonstrated that the turnover numbers of the current reaction could be up to 335.

Synthesis of Chiral Sulfoximines via Iridium-Catalyzed Regio- and Enantioselective C-H Borylation: A Remarkable Sidearm Effect of Ligand

Transition metal-catalyzed enantioselective C-H activation of prochiral sulfoximines for non-annulated products remains a formidable challenge. We herein report iridium-catalyzed enantioselective C-H borylation of N-silyl diaryl sulfoximines using a well-designed chiral bidentate boryl ligand with a bulky side arm. This method is capable of accommodating a broad range of substrates under mild reaction conditions, affording a vast array of chiral sulfoximines with high enantioselectivities. We also demonstrated the synthetic utility on a preparative-scale C-H borylation for diverse downstream transformations, including the synthesis of chiral version of bioactive molecules. Computational studies showed that the bulky side arm of the ligand confers high regio- and enantioselectivity through steric effect.

Atroposelective Synthesis of C-C Axially Chiral Compounds via Mono- and Dinuclear Vanadium Catalysis

Axially chiral compounds with rotationally constrained σ-bonds that exhibit atropisomerism are lucrative synthetic targets because of their ubiquity in functional materials and natural products. The metal complex-catalyzed enantioselective fabrication of axially chiral scaffolds has been widely investigated, and thus far, considerable progress has been made. Over the past two decades, we have developed a highly efficient strategy for constructing axially chiral biarenol derivatives using chiral mono- and dinuclear vanadium complexes. These complexes are readily prepared from vanadium(IV) salts and Schiff base ligands (generated from the condensation of (S)-tert-leucine and di- or monoformyl-(R)-1,1'-bi-2-naphthol (BINOL) derivatives) under O₂ and act as highly active catalysts for highly stereoselective C-C bond formation. In particular, the vanadium complex-catalyzed enantioselective oxidative coupling of 2-naphthols 1 under oxygen or in air, which is a green oxidant, affords the desired axially chiral molecules in high yields and high stereoselectivity (up to quantitative yield and 97% ee), along with water as the sole coproduct. This coupling reaction tolerated various functional groups (such as halogens, alkoxys, and boryls) and avoided overoxidation of coupling products.The key feature of dinuclear vanadium(V) catalysts such as (R_a,S,S)-5a is an outstanding mode of the homocoupling reaction, in which a single molecule of the catalyst activates two molecules of the starting material (e.g., 2-naphthols) simultaneously. With this "dual activation" mechanism, the oxidative coupling promoted by the dinuclear catalyst proceeds in an intramolecular manner. The homocoupling rate using 5 mol % of the dinuclear vanadium(V) complex (R_a,S,S)-5a was measured to be 111 times faster than that of the mononuclear vanadium(IV) complex (S)-4a bearing a half motif of the dinuclear vanadium complex.In the case of the heterocoupling reaction utilizing two different kinds of arenol derivatives, only a starting arenol having lower oxidation potential seems to be activated by the mononuclear vanadium complex. The reaction rate of the heterocoupling using either mono- or dinuclear vanadium complexes showed no difference to give the coupling product in high yields but with a different enantioselective manner; chiral mononuclear vanadium(V) complexes showed better enantioselectivites than that of the dinuclear vanadium(V) complexes. A competing heterocoupling study and a linear correlation between the ee of the mononucaler vanadium catalyst and ee of the heterocoupling suggested that the heterocoupling involves an intermolecular radical-anion coupling pathway.In this Account, we summarize the recent advances in vanadium-catalyzed coupling reactions that produced important chiral molecules, such as biresorcinols, polycyclic biphenols, oxa[9]helicenes, bihydroxycarbazoles, and C₁-symmetrical biarenols, and their coupling reaction mechanisms. By pursuing vanadium catalysis, we believe numerous additional transformations as well as a renewed interest in catalytic and chemo-, regio-, and enantioselective aryl-aryl bond constructions will be manifested.

Remote Site-Selective Asymmetric Protoboration of Unactivated Alkenes Enabled by Bimetallic Relay Catalysis

A remote C(sp³ )-H bond asymmetric borylation of unactivated alkenes was achieved by bimetallic relay catalysis. The reaction proceeded through reversible and consecutive β-H elimination/olefin insertion promoted by CoH species generated in situ, followed by copper-catalyzed asymmetric protoboration. The use of this synergistic Co/Cu catalysis protocol allowed the enantioselective protoboration of various unactivated terminal alkenes and internal alkenes, as well as an unrefined mixture of olefin isomers, at the distal less-reactive β-position to a functional group, leading to chiral organoboronates.

Metal-catalysed C-H bond activation and borylation

Transition metal-catalysed direct borylation of hydrocarbons via C-H bond activation has received a remarkable level of attention as a popular reaction in the synthesis of organoboron compounds owing to their synthetic versatility. While controlling the site-selectivity was one of the most challenging issues in these C-H borylation reactions, enormous efforts of several research groups proved instrumental in dealing with selectivity issues that presently reached an impressive level for both proximal and distal C-H bond borylation reactions. For example, in the case of ortho C-H bond borylation reactions, innovative methodologies have been developed either by the modification of the directing groups attached with the substrates or by creating new catalytic systems via the design of new ligand frameworks. Whereas meta and para selective C-H borylations remained a formidable challenge, numerous innovative concepts have been developed within a very short period of time by the development of new catalytic systems with the employment of various noncovalent interactions. Moreover, significant advancements have occurred for aliphatic C(sp³)-H borylations as well as enantioselective borylations. In this review article, we aim to discuss and summarize the different approaches and findings related to the development of directed proximal ortho, distal meta/para, aliphatic (racemic and enantioselective) borylation reactions since 2014. Additionally, considering the C-H borylation reaction as one of the most important mainstream reactions, various applications of this C-H borylation reaction toward the synthesis of natural products, therapeutics, and applications in materials chemistry will be summarized in the last part of this review article.

Iridium-Catalyzed Enantioselective C(sp3 )-H Borylation of Aminocyclopropanes

Transition-metal-catalyzed regio- and stereo-controllable C-H functionalization remains a formidable challenge in asymmetric catalysis. Herein, we disclose the first example of iridium-catalyzed C(sp³ )-H borylation of aminocyclopropanes by using simple imides as weakly coordinating directing groups under mild reaction conditions. The reaction proceeded via a six-membered iridacycle, affording a vast range of chiral aminocyclopropyl boronates. The current method features a broad spectrum of functional groups (36 examples) and high enantioselectivities (up to 99 %). We also demonstrated the synthetic utility by a preparative scale C-H borylation, C-B bond transformations, and conversion of the directing group.