Recent Advances in Hydrometallation of Alkenes and Alkynes via the First Row Transition Metal Catalysis

Cobalt-Catalyzed Regioselective Intramolecular Hydrosilylation of Olefins to Access Sila-heterocycles

An efficient and straightforward cobalt-catalyzed regioselective intramolecular hydrosilylation of olefins has been developed. Regioselectivity is controlled by the choice of ligands and substrates, which operate through two distinct mechanisms. This method has been successfully applied to both terminal and internal alkenes and phenyl and alkyl tethers between the silane and the alkene, demonstrating its versatility across a broad range of substrates.

Iron-Catalyzed Transfer Hydroalumination of Alkynes

The limited availability of efficient synthetic methods for organoaluminum compounds constrains their broader applications. The transfer hydroalumination of alkynes emerges as a promising strategy for synthesizing alkenylaluminum species; however, achieving precise control of the selectivity remains a formidable challenge. Herein, we disclose a highly chemo-, regio-, and stereoselective transfer hydroalumination of alkynes, catalyzed by well-defined iron complexes, utilizing commercially available AlEt3 as the hydroalumination reagent. The regioselectivity of the transfer hydroalumination reaction involving terminal alkynes can be effectively modulated by changing the 2,9-aryl substituents on the ligands with the observation of cis-α-selectivity not previously documented in the literature. Furthermore, we demonstrate unprecedented cis-β-selective transfer hydroalumination of simple unsymmetrical internal alkynes. This work not only broadens the scope of transfer hydroalumination reactions but also enhances the synthetic methodologies and diversity of organoaluminum compounds, highlighting the significant potential of iron catalysts in the development of organometallic reagents.

Heteroatom-Assisted Regio- and Stereoselective Hydrosilylation of Unsymmetric Internal Alkynes by Scandium Catalyst

The catalytic hydrosilylation of alkynes with hydrosilanes is the most straightforward and atom-efficient method for the synthesis of silylalkenes. However, the hydrosilylation of unsymmetrical internal alkynes often encounters regio- and stereoselectivity challenges. Herein, we report the regio- and syn-stereoselective hydrosilylation of unsymmetrical internal alkynes bearing heteroatom functional groups with hydrosilanes by half-sandwich scandium catalyst. This protocol offers an atom-efficient route for the synthesis of a new family of heteroatom (O, S or N)-functionalized multisubstituted silylalkenes from a variety of internal homopropargyl thioethers, ethers and tertiary amines and hydrosilanes, featuring 100 % atom-efficiency, broad substrate scope, and excellent regio- and syn-stereoselectivity (>19 : 1 r.r. and >19 : 1 syn/anti). The mechanistic details have been elucidated by control experiments and isolation and examination of some key reaction intermediates. It was revealed that an interaction between the heteroatom (O, S or N) in the internal alkynes and the Sc center was critical for achieving the unprecedented high selectivity.

The stereo-divergent functionalization of alkynes: a comprehensive review

Alkynes are central in crafting pharmaceuticals, agrochemicals, and materials owing to their reactivity and linear geometry. This review unveils cutting-edge advancements in the stereo-divergent functionalization of alkynes, transforming them into invaluable tools for synthesizing stereochemically defined alkenes and alkanes. The review highlights ground-breaking methodologies that achieve exceptional E- and Z-selectivity using innovative catalysts like cobalt, nickel, and palladium through hydrogenation, hydroboration, and hydrosilylation. Recent breakthroughs such as dual-catalytic systems and energy transfer catalysis enable unprecedented stereocontrol. Sustainable strategies including water as a hydrogen source and recyclable catalysts align with green chemistry principles, paving the way for eco-friendly synthesis. This synthesis of cutting-edge techniques and their applications inspire new avenues in synthetic chemistry, offering transformative tools for creating complex molecular architectures with precision and sustainability.

Enantioselective Synthesis of α-Hydroxy Allyl Ketones via BINAP-CuH-Catalyzed Hydroacylation

Catalytic hydrocupration of unsaturated carbon-carbon bonds to generate organometallic nucleophiles has recently become an attractive alternative to conventional stoichiometric reagents in the stereoselective synthesis. Herein, we have developed an efficient and economical method to synthesize enantiopure α-hydroxy allyl ketones via a copper hydride (CuH)-catalyzed hydroacylation of alkoxyallenes, a significant advancement given the scarcity of reports on such scaffolds in the literature. DFT calculations reveal that this reaction proceeds through the nucleophilic attack of a kinetically favourable Z-selective allyl-copper intermediate on acid anhydrides via a six-membered chair-like transition state, stabilized by strongly attractive non-covalent interactions that ultimately leads to high level of enantioselectivities using the simple BINAP ligand. This method successfully overcomes the challenges of over-reduction of carbonyl functionality in the presence of CuH-complex, olefin isomerization and the presence of a highly enolizable α-stereocenter, which can lead to erosion in enantioselectivities, making our strategy highly desirable. The reaction exhibits a wide range of substrate scope including symmetrical as well as carbonic anhydrides with both aromatic, and aliphatic substitutions. In addition, α-substituted acid anhydrides provide exclusive syn-selective α,α'-disubstituted allyl ketones in excellent enantiomeric ratios, where the nucleophilic allylation occurs on one of the carbonyls containing the matched α-stereocenter, confirmed with mechanistic studies.

Cobalt-Catalyzed Remote Site-Selective Hydroboration of Unactivated Alkenes via Chain-Walking Strategy

An expedient synthesis of α-aminoboronic acid derivatives via cobalt-catalyzed remote site-selective hydroboration of unactivated alkenes is described herein. The strategy is characterized by its simplicity, site-selectivity, and wide substrate scope, as both terminal and internal alkenes could undergo the reaction smoothly, affording the corresponding products in good yields. According to the mechanism, Co-H is generated from Co(acac)2 in the presence of HBpin, which starts the chain-walking strategy via a series of alkene insertion and β-H elimination process.

Chemodivergent, enantio- and regioselective couplings of alkynes, aldehydes and silanes enabled by nickel/N-heterocyclic carbene catalysis

Divergent synthesis of valuable molecules through common starting materials and metal catalysis represents a longstanding challenge and a significant research goal. We here describe chemodivergent, highly enantio- and regioselective nickel-catalyzed reductive and dehydrogenative coupling reactions of alkynes, aldehydes, and silanes. A single chiral Ni-based catalyst is leveraged to directly prepare three distinct enantioenriched products (silyl-protected trisubstituted chiral allylic alcohols, oxasilacyclopentenes, and silicon-stereogenic oxasilacyclopentenes) in a single chemical operation. The use of a bulky C2-symmetric N-heterocyclic carbene (NHC) ligand for nickel catalyst is the key to enable simultaneous exceptional control of stereo- and regioselectivity (up to 99% enantiomeric excess (ee), >99:1 regiomeric ratio (rr), >99:1 E/Z) and high efficiency (up to 99% yield). Computational studies elucidate the origin of chemodivergency and reveal the critical role of NHC in the enantioselectivity- and rate-determining oxidative cyclization step via an η2-aldehyde η2-alkyne Ni five-centered transition state. We expected that the enantioselective η2-activation mode be widely applicable in other Ni-catalyzed carbonyl couplings.

Nickel-Catalyzed Linear-Selective C-H Alkylation of N-Heteroarenes with Unactivated α-Olefins

We herein describe the nickel-catalyzed C2-H alkylation of benzothiazoles with unactivated α-olefins by using the Ni(IPr*OMe)[P(OEt)3]Br2/Mg catalytic system in which a variety of linear alkylated benzothiazoles with high regioselectivity were formed under mild reaction conditions. This transformation showed good compatibility to unactivated α-olefins bearing various functional groups, such as esters, acetals, silyl ethers, amines, silanes, and boronate esters. Furthermore, this transformation is also suitable to other typical N-heteroarenes including thiazoles, benzimidazoles, quinazolones, uracils, pyridines, caffeines, and indoles. Thus, this work provides rapid access to diverse linear alkylated N-heteroarenes with good step and atom economy.

Ruthenium-Catalyzed α-Regioselective Hydroboration of Allenes

Hydroboration of allenes is powerful and atom-economic approach to the synthesis of organoboranes, such as the highly versatile allylboranes. However, regarding regiocontrol, existing methods uniformly deliver the boron functionality to the less hindered β- or γ-position, but not the α-position. The latter is particularly challenging for allenes with substantial steric difference between the two terminals and lacking electronic bias (e.g., 1,1-disubstituted allenes). Herein we report the first highly efficient ruthenium-catalyzed hydroboration of allenes featuring exclusive α-regioselectivity, providing access to sterically hindered allyl boranes that are limitedly accessible by conventional methods. DFT studies suggested that the unusual α-regioselectivity is attributed to the disfavored reductive elimination at the γ-position due to the high energy cost required to overcome the agostic interaction and rotation of the key π-allyl intermediates. This protocol is also applicable to the previously unprecedented α-hydroalkynylation and underdeveloped α-hydrosilylation of allenes, thus complementing known catalytic systems and providing convenient access to highly congested yet densely-functionalized allyl silanes and skipped enynes bearing a fully-substituted allylic carbon center. It is expected that this ruthenium-catalyzed system can serve as a new platform for the development of other hydrofunctionalization processes with unorthodox selectivity.

Rhodium-Catalyzed Enantioselective Hydrosilylation of 1,1-Disubstituted Enamides

Catalytic hydrosilylation of 1,1-disubstituted enamides is one of the most challenging and synthetically useful processes in organosilicon chemistry and asymmetric catalysis. Herein, we report a rhodium-catalyzed enantioselective hydrosilylation of α-arylenamides with substituted hydrosilanes with the aid of chiral P-ligand, including newly developed spirophosphite ligands, giving various chiral β-silylated amides in excellent yields with good to excellent enantioselectivities (98:2 er after recrystallization). In addition, chiral β-silylated amines can be obtained by further functionalization of the hydrosilylation product.

Computational Insights into the Effect of Ligands and Transition-Metal Centers on the Mechanism and Regioselectivity of Hydrosilylation of Alkenes

Development of sustainable synthetic methods for the hydrosilylation of alkenes, catalyzed by 3d transition metals, offers a promising alternative to traditional noble metal catalysts. This study presents a computational mechanistic investigation into the hydrosilylation of alkenes, focusing on the role of ligands and metal centers in modulating the reaction's mechanism and regioselectivity. The ligand's electronic and steric properties were found to modulate the regioselectivity for cobalt catalysts, with phosphine ligand (xantphos) promoting higher linear selectivity compared to nitrogen-based ligand (mesPDI). The energy decomposition analysis reveals that the xantphos ligand favors linear products due to stronger electrostatic and orbital interactions despite increased steric repulsion. The metal center also plays a crucial role, with cobalt catalysts favoring the modified Chalk-Harrod mechanism for branched product formation in the presence of PNN ligand (iPrPCNNMe), due to lower activation barriers in alkene insertion. Beneficial electrostatic and orbital interactions predominate, rendering the alkene insertion transition state for cobalt more favorable compared to that for iron. This work provides a comprehensive understanding of how ligand and metal center effects can be harnessed to control regioselectivity in hydrosilylation reactions.

Nickel-Catalyzed α-selective Hydroalkylation of Vinylarenes

C(sp3) centers adjacent to (hetero) aryl groups are widely present in physiologically active molecules. Metal-hydride-catalyzed hydroalkylation of alkenes represents an efficient means of forging C(sp3)-C(sp3) bonds, boasting advantages as a wide source of substrates, mild reaction conditions, and facile selectivity manipulation. Nevertheless, the hydroalkylation of vinylarenes encounters constraints in terms of substrate scope, necessitating the employment of activated alkyl halides or alkenes containing chelating groups, remains a challenge. In this context, we report a general nickel-hydride-catalyzed hydroalkylation protocol for vinylarenes. Remarkably, this system enables α-selective hydroalkylation of both aryl and heteroaryl alkenes under an extra ligand-free condition, demonstrating excellent coupling efficiency and selectivity. Furthermore, through the incorporation of chiral bisoxazoline ligands, we have achieved regio- and enantioselective hydroalkylation of vinylpyrroles, thereby facilitating the synthesis of α-branched alkylated pyrrole derivatives.

Dirhodium(II)/XantPhos Catalyzed Synthesis of β-(E)-Vinylsilanes via Hydrosilylation and Isomerization from Alkynes

A concise hydrosilylation of alkynes for synthesizing β-(E)-vinylsilanes catalyzed by dirhodium(II)/XantPhos has been developed. In this reaction, β-(E)-vinylsilanes were generated from the isomerization of β-(Z)-vinylsilanes catalyzed by dirhodium(II) hydride species rather than the direct insertion of triple bond into M-H or M-Si bond (traditional Chalk-Harrod mechanism or modified Chalk-Harrod mechanism). The hydrosilylation displayed a broad substrate scope for alkynes and tertiary silanes, tolerating diverse functional groups including halides, nitriles, amines, esters, and heterocycles.

Metal-Hydride C-C Cross-Coupling of Alkenes Through a Double Outer-Sphere Mechanism

This Synopsis covers recent reports of metal-catalyzed alkene functionalizations that likely involve iterative outer-sphere reactions in which the substrate reacts directly with a metal ligand instead of with the metal center itself. Traditional metal hydride-catalyzed alkene functionalizations involve this latter pathway whereby the alkene forms part of the metal ligand sphere (i.e. an inner-sphere reaction). In contrast, alkenes do not ligate the metal in so-called outer-sphere reactions and instead react with a metal ligand. These transformations have proved crucial for the synthesis of high fraction sp3 (Fsp3) targets, especially in hindered fragment couplings of relevance to natural product space.

Regio- and Enantioselective Nickel-Catalyzed Ipso- and Remote Hydroamination Utilizing Organic Azides as Amino Sources for the Synthesis of Primary Amines

Primary amines serve as key synthetic precursors to most other N-containing compounds, which are important in organic and medicinal chemistry. Herein, we present a NiH-catalyzed mild ipso- and remote hydroamination technique that utilizes organic azides as deprotectable primary amine sources. This strategy offers a highly flexible platform for the efficient construction of α-chiral branched primary amines, as well as linear primary amines.

Ligand-controlled regiodivergent arylation of aryl(alkyl)alkynes and asymmetric synthesis of axially chiral 9-alkylidene-9,10-dihydroanthracenes

Transition metal-catalyzed addition of organometallics to aryl(alkyl)alkynes has been well known to proceed with the regioselectivity in forming a carbon-carbon bond at the alkyl-substituted carbon (β-addition). Herein, the reverse regiochemistry with high selectivity in giving 1,1-diarylalkenes (α-addition) was realized in the reaction of arylboronic acids with aryl(alkyl)alkynes by use of a rhodium catalyst coordinated with a chiral diene ligand, whereas the arylation of the same alkynes proceeded with the usual regioselectivity (β-addition) in the presence of a rhodium/DM-BINAP catalyst. The regioselectivity can be switched by the choice of ligands on the rhodium catalysts. This reverse regioselectivity also enabled the catalytic asymmetric synthesis of phoenix-like axially chiral alkylidene dihydroanthracenes with high enantioselectivity through an α-addition/1,4-migration/cyclization sequence.

Copper-Catalyzed Regiodivergent Asymmetric Difunctionalization of Terminal Alkynes

We herein describe the first example of ligand-controlled, copper-catalyzed regiodivergent asymmetric difunctionalization of terminal alkynes through a cascade hydroboration and hydroallylation process. The catalytic system, consisting of (R)-DTBM-Segphos and CuBr, could efficiently achieve asymmetric 1,1-difunctionalization of aryl terminal alkynes, while ligand switching to (S,S)-Ph-BPE could result in asymmetric 1,2-difunctionalization exclusively. In addition, alkyl substituted terminal alkynes, especially industrially relevant acetylene and propyne, were also valid feedstocks for asymmetric 1,1-difunctionalization. This protocol is characterized by good functional group tolerance, a broad scope of substrates (>150 examples), and mild reaction conditions. We also showcase the value of this method in the late-stage functionalization of complicated bioactive molecules and simplifying the synthetic routes toward the key intermediacy of natural product (bruguierol A). Mechanistic studies combined with DFT calculations provide insight into the mechanism and origins of this ligand-controlled regio- and stereoselectivity.

Enantioselective Copper-Catalyzed Sequential Hydrosilylation of Arylmethylenecyclopropanes

Despite impressive advances in the construction of enantioenriched silacarbocycles featuring silicon-stereogenic centers via a selection of well-defined sila-synthons, the development of a more convenient and economic method with readily available starting materials is significantly less explored and remains a considerable challenge. Herein, we report the first example of copper-catalyzed sequential hydrosilylation of readily accessible methylenecyclopropanes (MCPs) and primary silanes, affording an efficient and convenient route to a wide range of chiral silacyclopentanes bearing consecutive silicon- and carbon-stereogenic centers with excellent enantio- and diastereoselectivities (generally ≥98 % ee, >25 : 1 dr). Mechanistic studies reveal that these reactions combine copper-catalyzed intermolecular ring-opening hydrosilylation of aryl MCPs and intramolecular asymmetric hydrosilylation of the resultant Z/E mixture of homoallylic silanes.

Cobalt-catalyzed hydrothiolation of alkynes for the diverse synthesis of branched alkenyl sulfides

Alkenyl sulfides have gained increasing prominence in medicinal chemistry and materials. Hydrothiolation of alkynes for the diverse synthesis of alkenyl sulfides is an appealing method. Herein, we report a cobalt-catalyzed Markovnikov hydromethylthiolation of alkynes to afford branched alkenyl methylsulfanes with good yields and high regioselectivity. This method also enables the diverse synthesis of branched alkenyl sulfides. The reaction shows good functional group tolerance and could be scaled up. The mechanistic studies including control experiments, deuterium-labeling experiments, and Hammett plot indicated alkynes insertion followed by electrophilic thiolation pathway.

Regio-, stereo-, and enantioselective ipso- and migratory defluorinative olefin cross-coupling to access highly functionalized monofluoroalkenes

Monofluoroalkenes serve as nonhydrolyzable mimetics of amides and are frequently encountered in drug candidates. Herein we report a regio-, enantio-, and stereoselective NiH-catalyzed ipso- and migratory defluorinative olefin cross-coupling employing readily available olefins and gem-difluoroalkenes under mild conditions. This approach enables the efficient synthesis of a broad array of structurally diverse monofluoroalkenes bearing a tertiary allylic stereogenic center. Mechanistically, the challenging migratory defluorinative olefin cross-coupling process is successfully realized through a ligand relay catalytic strategy, enabling the formal C(sp3)-H/C(sp2)-F activation with high levels of regio-, stereo-, and enantiocontrol.

Metal-catalyzed Markovnikov-type selective hydrofunctionalization of terminal alkynes

Metal-catalyzed highly Markovnikov-type selective hydrofunctionalization of terminal alkynes provides a straightforward and atom-economical route to access 1,1-disubstituted alkenes, which have a wide range of applications in organic synthesis. However, the highly Markovnikov-type selective transformations are challenging due to the electronic and steric effects during the addition process. With the development of metal-catalyzed organic synthesis, different metal catalysts have been developed to solve this challenge, especially for platinum group metal catalysts. In this perspective, we review homogeneous metal-catalyzed Markovnikov-type selective hydrofunctionalization of terminal alkynes according to the classified element types as well as reaction mechanisms. Future avenues for investigation are also presented to help expand this exciting field.

Regio- and Enantioselective Hydromethylation of 3-Pyrrolines and Glycals Enabled by Cobalt Catalysis

Enantioenriched 3-methylpyrrolidine, with its unique chiral nitrogen-containing core skeleton, exists widely in various functional molecules, including natural products, bioactive compounds, and pharmaceuticals. Traditional methods for synthesizing these valuable methyl-substituted heterocycles often involve enzymatic processes or complex procedures with chiral auxiliaries, limiting the substrate scope and efficiency. Efficient catalytic methylation, especially in an enantioselective manner, has been a long-standing challenge in chemical synthesis. Herein, we present a novel approach for the remote and stereoselective installation of a methyl group onto N-heterocycles, leveraging a CoH-catalyzed asymmetric hydromethylation strategy. By effectively combining a commercial cobalt precursor with a modified bisoxazoline (BOX) ligand, a variety of easily accessible 3-pyrrolines can be converted to valuable enantiopure 3-(isotopic labeling)methylpyrrolidine compounds with outstanding enantioselectivity. This efficient protocol streamlines the two-step synthesis of enantioenriched 3-methylpyrrolidine, which previously required up to five or six steps under harsh conditions or expensive starting materials.

Reversal of the Regioselectivity of Iron-Promoted Hydrogenation and Hydrohalogenation of gem-Difluoroalkenes

The reaction regioselectivity of gem-difluoroalkenes is dependent on the intrinsic polarity. Thus, the reversal of the regioselectivity of the addition reaction of gem-difluoroalkenes remains a formidable challenge. Herein, we described an unprecedented reversal of regioselectivity of hydrogen atom transfer (HAT) to gem-difluoroalkenes triggered by Fe-H species for the formation of difluoroalkyl radicals. Hydrogenation of the in situ generated radicals gave difluoromethylated products. Mechanism experiments and theoretical studies revealed that the kinetic effect of the irreversible HAT process resulted in the reversal of the regioselectivity of this scenario, leading to the formation of a less stable α-difluoroalkyl radical regioisomer. On basis of this new reaction of gem-difluoroalkene, the iron-promoted hydrohalogenation of gem-difluoroalkenes for the efficient synthesis of aliphatic chlorodifluoromethyl-, bromodifluoromethyl- and iododifluoromethyl-containing compounds was developed. Particularly, this novel hydrohalogenation of gem-difluoroalkenes provided an effect and large-scale access to various iododifluoromethylated compounds of high value for synthetic application.

Ligand-Controlled Cobalt-Catalyzed Regiodivergent and Stereoselective Ring-Opening Isomerization of Vinyl Cyclopropanes

A ligand-controlled regiodivergent and stereoselective ring-opening isomerization of vinylcyclopropane was developed with cobalt catalysis. Employing the commercially available Xantphos ligand, the reactions afforded exclusively linear-type 1,3-dienes as the products. Interestingly, when switching the ligand to an amido-diphosphine ligand (PNP), branched-type 1,3-dienes were obtained with high regioselectivity and stereoselectivity. Preliminary mechanistic investigations suggested that a π-allyl metal and a metal-hydride species are involved as key intermediates in the two transformations, respectively.

CoH-catalyzed asymmetric remote hydroalkylation of heterocyclic alkenes: a rapid approach to chiral five-membered S- and O-heterocycles

Saturated heterocycles, which incorporate S and O heteroatoms, serve as fundamental frameworks in a diverse array of natural products, bioactive compounds, and pharmaceuticals. Herein, we describe a unique cobalt-catalyzed approach integrated with a desymmetrization strategy, facilitating precise and enantioselective remote hydroalkylation of unactivated heterocyclic alkenes. This method delivers hydroalkylation products with high yields and excellent stereoselectivity, representing good efficiency in constructing alkyl chiral centers at remote C3-positions within five-membered S/O-heterocycles. Notably, the broad scope and good functional group tolerance of this asymmetric C(sp3)-C(sp3) coupling enhance its applicability.

Rhodium-Catalyzed Highly Enantioselective Hydroboration of Acyclic Tetrasubstituted Alkenes Directed by an Amide

Although progress has been made in enantioselective hydroboration of di- and trisubstituted alkenes over the past decades, enantioselective hydroboration of tetrasubstituted alkenes with high diastereo- and enantioselectivities continues as an unmet challenge since the 1950s due to its extremely low reactivity and the difficulties to simultaneously control the regio- and stereoselectivity of a tetrasubstituted alkene. Here, we report highly regio-, diastereo-, and enantioselective catalytic hydroboration of diverse acyclic tetrasubstituted alkenes. The delicate interplay of an electron-rich rhodium complex and coordination-assistance forms a highly adaptive catalyst that effectively overcomes the low reactivity and controls the stereoselectivity. The generality of the catalyst system is exemplified by its efficacy across various tetrasubstituted alkenes with diverse steric and electronic properties.

Recent advances in earth-abundant transition metal-catalyzed dihydrosilylation of terminal alkynes

Over the past few years, earth-abundant transition metal-catalyzed hydrosilylation has emerged as an ideal strategy for the synthesis of organosilanes. The success in this area of research has expanded to the advancements of alkyne dihydrosilylation reactions, offering broadened synthetic applications through the selective installation of two silyl groups. In particular, catalysts based on Fe, Co, and Ni have engendered enabling platforms for mild transformations with a range of distinct regioselectivity. This mini-review summarizes recent advances in this research field, highlighting the unique features of each system from both synthetic and mechanistic perspectives.

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.

Enantioselective synthesis of chiral α,α-dialkyl indoles and related azoles by cobalt-catalyzed hydroalkylation and regioselectivity switch

General, catalytic and enantioselective construction of chiral α,α-dialkyl indoles represents an important yet challenging objective to be developed. Herein we describe a cobalt catalyzed enantioselective anti-Markovnikov alkene hydroalkylation via the remote stereocontrol for the synthesis of α,α-dialkyl indoles and other N-heterocycles. This asymmetric C(sp3)-C(sp3) coupling features high flexibility in introducing a diverse set of alkyl groups at the α-position of chiral N-heterocycles. The utility of this methodology has been demonstrated by late-stage functionalization of drug molecules, asymmetric synthesis of bioactive molecules, natural products and functional materials, and identification of a class of molecules exhibiting anti-apoptosis activities in UVB-irradiated HaCaT cells. Ligands play a vital role in controlling the reaction regioselectivity. Changing the ligand from bi-dentate L6 to tridentate L12 enables CoH-catalyzed Markovnikov hydroalkylation. Mechanistic studies disclose that the anti-Markovnikov hydroalkylation involves a migratory insertion process while the Markovnikov hydroalkylation involves a MHAT process.

Advances in disilylation reactions to access cis/trans-1,2-disilylated and gem-disilylated alkenes

Organosilane compounds are widely used in both organic synthesis and materials science. Particularly, 1,2-disilylated and gem-disilylated alkenes, characterized by a carbon-carbon double bond and multiple silyl groups, exhibit significant potential for subsequently diverse transformations. The versatility of these compounds renders them highly promising for applications in materials, enabling them to be valuable and versatile building blocks in organic synthesis. This review provides a comprehensive summary of methods for the preparation of cis/trans-1,2-disilylated and gem-disilylated alkenes. Despite notable advancements in this field, certain limitations persist, including challenges related to regioselectivity in the incorporation and chemoselectivity in the transformation of two nearly identical silyl groups. The primary objective of this review is to outline synthetic methodologies for the generation of these alkenes through disilylation reactions, employing silicon reagents, specifically disilanes, hydrosilanes, and silylborane reagents. The review places particular emphasis on investigating the practical applications of the C-Si bond of disilylalkenes and delves into an in-depth discussion of reaction mechanisms, particularly those reactions involving the activation of Si-Si, Si-H, and Si-B bonds, as well as the C-Si bond formation.

Dirhodium(II)/DPPM Catalyzed 1,2-Hydrosilylation of Conjugated Dienes with Tertiary Silanes

A simple and efficient Rh2(OAc)4/DPPM (bis(diphenylphosphanyl)methane) catalyzed regioselective 1,2-anti-Markovnikov hydrosilylation of conjugated dienes with various tertiary silanes gave homoallylic silanes in acetonitrile, which tolerate broad functional groups. Control experiments proved that no π-allyl transition metal intermediates were involved in this 1,2-anti-Markovnikov hydrosilylation. Dirhodium hydride species was observed in hydrosilylation, suggesting that a direct insertion of the terminal double bond into a Rh-H bond is involved in this reaction.

Protocol for iron-catalyzed cross-electrophile coupling of aryl chlorides with unactivated alkyl chlorides

Organochlorides are a crucial class of electrophiles in organic synthesis. Here, we present a protocol for the cross-electrophile coupling of aryl chlorides with unactivated alkyl chlorides, facilitated by an iron/B2pin2 catalytic system. We describe steps for the coupling of aryl chlorides with alkyl chlorides, followed by purification of products. This protocol can produce alkylated products with up to 81% yield. For complete details on the use and execution of this protocol, please refer to Zhang et al.1.

Cobalt catalyzed practical hydroboration of terminal alkynes with time-dependent stereoselectivity

Stereodefined vinylboron compounds are important organic synthons. The synthesis of E-1-vinylboron compounds typically involves the addition of a B-H bond to terminal alkynes. The selective generation of the thermodynamically unfavorable Z-isomers remains challenging, necessitating improved methods. Here, such a proficient and cost-effective catalytic system is introduced, comprising a cobalt salt and a readily accessible air-stable CNC pincer ligand. This system enables the transformation of terminal alkynes, even in the presence of bulky substituents, with excellent Z-selectivity. High turnover numbers (>1,600) and turnover frequencies (>132,000 h-1) are achieved at room temperature, and the reaction can be scaled up to 30 mmol smoothly. Kinetic studies reveal a formal second-order dependence on cobalt concentration. Mechanistic investigations indicate that the alkynes exhibit a higher affinity for the catalyst than the alkene products, resulting in exceptional Z-selective performance. Furthermore, a rare time-dependent stereoselectivity is observed, allowing for quantitative conversion of Z-vinylboronate esters to the E-isomers.

Cobalt-Catalyzed Asymmetric Hydrogenation: Substrate Specificity and Mechanistic Variability

Asymmetric hydrogenation finds widespread application in academia and industry. And indeed, a number of processes have been implemented for the production of pharma and agro intermediates as well as flavors & fragrances. Although these processes are all based on the use of late transition metals as catalysts, there is an increasing interest in the use of base metal catalysis in view of their lower cost and the expected different substrate scope. Catalysts based on cobalt have already shown their potential in enantioselective hydrogenation chemistry. This review outlines the impressive progress made in recent years on cobalt-catalyzed asymmetric hydrogenation of different unsaturated substrates. We also illustrate the ligand dependent substrate specificity as well as the mechanistic variability in detail. This may well guide further catalyst development in this research area.

Selective Access to Silacyclopentanes and Homoallylsilanes by La-Catalyzed Hydrosilylations of 1-Aryl Methylenecyclopropanes

Methylenecyclopropanes (MCPs) have emerged as versatile building blocks in synthetic chemistry because of their unique reactivity. However, metal-catalyzed hydrosilylation of MCPs has met with very limited successes. In this paper, catalytic selective hydrosilylations of MCPs with some primary silanes using an ene-diamido lanthanum ate complex as the catalyst were described. The catalytic reactions resulted in the selective formation of silacyclopentanes and (E)-homoallylsilanes, respectively, depending on the substituents on MCPs. The formation of silacyclopentanes via a catalytic cascade inter- and intramolecular hydrosilylation mechanism is strongly supported by the control and deuteration-labeling experiments and DFT calculations. The unique reactivity and selectivity could be attributed to the large lanthanum ion and ate structure of the catalyst.

Ligand-Controlled On-Off Switch of a Silicon-Tethered Directing Group Enabling the Regiodivergent Hydroalkylation of Vinylsilanes under Ni-H Catalysis

A regiodivergent Ni-H-catalyzed hydroalkylation of vinylsilanes is described. Depending on the ancillary ligand at the nickel catalyst, the regioselectivity can be steered by a directing group attached to the silicon atom. The mild protocols allow for the selective synthesis of either branched or linear alkylsilanes. An example of a vinylgermane is also reported. The method features a broad scope with high functional-group tolerance and follows a radical mechanism.

Ligand-Controlled Cobalt-Catalyzed Regio-, Enantio-, and Diastereoselective Oxyheterocyclic Alkene Hydroalkylation

Metal-hydride-catalyzed alkene hydroalkylation has been developed as an efficient method for C(sp3)-C(sp3) coupling with broad substrate availability and high functional group compatibility. However, auxiliary groups, a conjugated group or a chelation-directing group, are commonly required to attain high regio- and enantioselectivities. Herein, we reported a ligand-controlled cobalt-hydride-catalyzed regio-, enantio-, and diastereoselective oxyheterocyclic alkene hydroalkylation without chelation-directing groups. This reaction enables the hydroalkylation of conjugated and unconjugated oxyheterocyclic alkenes to deliver C2- or C3-alkylated tetrahydrofuran or tetrahydropyran in uniformly good yields and with high regio- and enantioselectivities. In addition, hydroalkylation of C2-substituted 2,5-dihydrofuran resulted in the simultaneous construction of 1,3-distereocenters, providing convenient access to polysubstituted tetrahydrofuran with multiple enantioenriched C(sp3) centers.

Nickel-Catalyzed Migratory Cross-Coupling Reactions: New Opportunities for Selective C-H Functionalization

ConspectusMigratory cross-coupling via metal migration is a process of significant academic and industrial interest. It provides an attractive alternative for the selective installation of a functional group at remote C-H positions from simple precursors, thus enabling the direct synthesis of challenging structures not accessible with traditional cross-coupling. In particular, with the merger of 1,n-Ni/H shift and cross-coupling of nickel, the Ni-catalyzed migratory functionalization of simple precursors has undergone particularly intense development and emerged as a valuable field of research in the past few years. This Account will outline the recent progress made in this arena in terms of migration-functionalization modes, diverse functionalizations, and strategies for regio- and stereocontrol. Mechanistic studies and synthetic applications are also discussed.In detail, we systematically categorize our work into two parts based on the migration modes. In the first part, a platform is created for Ni-catalyzed migratory sp3 C-H functionalization of alkenes or alkyl halides via iterative 1,2-Ni/H shift-selective cross-coupling. The key reactive Ni(II)H species for chain-walking could be generated in situ either in a polarity-reversed fashion relying on stoichiometric reductants (X-Ni(II)-H) or in a redox-neutral fashion with the participation of nucleophilic coupling partners (FG-Ni(II)-H). One significant advantage associated with the polarity-reversed NiH system is the use of relatively stable, abundant, and safe olefin surrogates or alkyl halides instead of the sensitive organometallics required in traditional cross-coupling reactions. Another advantage is that diverse functionalizations, including carbonation and more challenging amination and thiolation could be smoothly achieved with suitable electrophiles or their precursors. Finally, to address the challenging multifaceted selectivity and reactivity issues in asymmetric migratory cross-coupling reactions, we have developed a feasible ligand relay catalytic strategy. In this dynamic ligand exchange process, one ligand promotes rapid migration while the other promotes highly regio- and stereoselective coupling. This innovative strategy overcomes the formidable challenge stemming from the difficulty of designing a single ligand to efficiently promote both steps of chain-walking and asymmetric coupling. In the second part, a new platform for Ni-catalyzed migratory sp2 C-H functionalization via 1,4-Ni/H shift-selective cross-coupling has been reported. Starting from readily available aryl or vinyl coupling partners, the in situ-generated aryl- or vinylnickel(II) species could undergo a rapid and reversible 1,4-Ni/H shift along an sp2 backbone, and subsequent selective coupling with various coupling partners would allow regio- and stereoselective access to diverse 1,4-migratory functionalization products. The key to success was the discovery of an appropriate ligand to efficiently promote both migration and subsequent selective cross-coupling. A vinyl-to-aryl 1,4-Ni/H shift successfully enables the modular ipso/ortho difunctionalization of aryl coupling partners, while an aryl-to-vinyl 1,4-Ni/H shift enables regio- and stereoselective access to functionalized trisubstituted alkenes.We hope that this Account will inspire broad interest and future development of migratory cross-coupling reactions. We strongly believe that continued efforts in this fascinating field will overcome many of the remaining challenges, including cutting-edge ligand/catalyst design to enhance reactivity and selectivity, conceptually new migration modes for additional transformations, and in-depth mechanistic studies for rational reaction design.

Nickel-Catalyzed Enantioselective Hydrothiocarbonylation of Cyclopropenes

Hydrothiocarbonylation of olefins using carbon monoxide and thiols is a powerful method to synthesize thioesters from simple building blocks. Owing to the intrinsic challenges of catalyst poisoning, transition-metal-catalyzed asymmetric thiocarbonylation, particularly when utilizing earth abundant metals, remains rare in the literature. Herein, we report a nickel-catalyzed enantioselective hydrothiocarbonylation of cyclopropenes for the synthesis of a diverse collection of functionalized thioesters in good to excellent yields with high stereoselectivity. This new method employs an inexpensive, air-stable nickel(II) precursor, which provides enhanced catalyst fidelity against CO poisoning compared to nickel(0) catalysts.

Highly Selective Nickel-Catalyzed Isomerization-Hydroboration of Alkenes Affords Terminal Functionalization at Remote C-H Position

We report herein the synthesis and characterization of nickel complexes supported by tridentate and bidentate phosphino(silyl) ancillary ligands, along with the successful application of these complexes as precatalysts for the hydroboration of terminal and internal alkenes using pinacolborane (HBPin). These reactions proceeded with low nickel loadings of 2.5-5 mol % in the absence of co-solvent, and in some cases at room temperature. Isomerization to afford exclusively the terminal hydroboration product was obtained across a range of internal alkenes, including tri- and tetra-substituted examples. This reactivity is unprecedented for nickel and offers a powerful means of achieving functionalization at a C-H position remote from the C=C double bond. Nickel-catalyzed deuteroboration experiments using DBPin support a mechanism involving 1,2-insertion of the alkene and subsequent chain-walking, which results in isotopic scrambling.

Copper-Catalyzed Regio- and Stereoselective Formal Hydro(borylmethylsilyl)ation of Internal Alkynes via Alkenyl-to-Alkyl 1,4-Copper Migration

Catalytic reactions involving 1,n-metal migration from carbon to carbon enable a nonclassical way of constructing organic molecular skeletons, rapidly providing complex molecules from relatively simple precursors. By utilization of this attractive feature, a new and efficient synthesis of alkenylsilylmethylboronates has been developed by formal hydro(borylmethylsilyl)ation of unsymmetric internal alkynes with silylboronates under copper catalysis. The reaction proceeds regioselectively and involves an unprecedented alkenyl-to-alkyl 1,4-copper migration. The reaction mechanism has been investigated by a series of kinetic, NMR, and deuterium-labeling experiments.

Transition-metal-catalyzed atroposelective synthesis of axially chiral styrenes

Axially chiral styrenes, a type of atropisomer analogous to biaryls, have attracted great interest because of their unique presence in natural products and asymmetric catalysis. Since 2016, a number of methodologies have been developed for the atroposelective construction of these chiral skeletons, involving both transition metal catalysis and organocatalysis. In this feature article, we aim to provide a comprehensive understanding of recent advances in the asymmetric synthesis of axially chiral styrenes catalyzed by transition metals, integrating scattered work with different catalytic systems together. This feature article is cataloged into five sections according to the strategies, including asymmetric coupling, enantioselective C-H activation, central-to-axial chirality transfer, asymmetric alkyne functionalization, and atroposelective [2+2+2] cycloaddition.

Activation of robust bonds by carbonyl complexes of Mn, Fe and Co

Metal carbonyl complexes possess among the most storied histories of any compound class in organometallic chemistry. Nonetheless, these old dogs continue to be taught new tricks. In this Feature, we review the historic discoveries and recent advances in cleaving robust bonds (e.g., C-H, C-O, C-F) using carbonyl complexes of three metals: Mn, Fe, and Co. The use of Mn, Fe, and Co carbonyl catalysts in controlling selectivity during hydrofunctionalization reactions is also discussed. The chemistry of these earth-abundant metals in the field of robust bond functionalization is particularly relevant in the context of sustainability. We expect that an up-to-date perspective on these seemingly simple organometallic species will emphasize the wellspring of reactivity that continues to be available for discovery.

Ru(OAc)3-Catalyzed Regioselective Difunctionalization of Alkynes: Access to (E)-2-Bromo-1-alkenyl Sulfonates

A new approach is proposed for the divergent and regioselective synthesis of (E)-2-bromo-1-phenylvinyl trifluoromethanesulfonates through alkyne difunctionalization by employing a compatible system of abundantly available alkynes, N-bromosuccinimide (NBS), and trimethylsilyl trifluoromethanesulfonate (TMSOTf) catalyzed by ruthenium(III) acetate [Ru(OAc)3]. It is a novel method for the preparation of vinyl triflate and it offers a fundamental basis for the development of advanced functional compounds, including drugs and organic functional materials. Unlike previously reported methods, the proposed protocol can tolerate a broad range of functional groups. Alkynes derived from bioactive molecules, such as l(-)-borneol, demonstrate the potential value of this new reaction in organic synthesis.

Synthesis of Enantioenriched 1,2-cis Disubstituted Cycloalkanes by Convergent NiH Catalysis

Enantioenriched multi-substituted cycloalkanes constitute an essential class of compounds in pharmaceuticals, natural products and agrochemicals. Here we report an NiH-catalyzed asymmetric migratory hydroalkylation process for the efficient and selective construction of such compounds. Through a dynamic kinetic asymmetric transformation (DYKAT), easily accessible racemic and isomeric mixtures of cycloalkenes could be directly utilized as starting materials, convergently producing thermo-dynamically disfavored chiral 1,2-cis disubstituted cycloalkanes bearing vicinal stereocenters with high levels of regio-, diastereo- and enantioselectivity. In addition, prochiral cyclic alkenes can be also employed, and deliver chiral 1,2-cis disubstituted cycloalkanes through desymmetrization process.

Asymmetric anti-Selective Borylalkylation of Terminal Alkynes by Nickel Catalysis

Selective transformation of alkyne triple bonds to double bonds serves as an efficient platform to construct substituted alkenes. While significant advances have been made in its spatiotemporal regulation, achieving a multicomponent enantioselective reaction that requires multifaceted selectivity issues to be overcome is still uncommon. Here, we report an unprecedented asymmetric anti-stereoselective borylcarbofunctionalization of terminal alkynes by nickel catalysis. The utilization of an inexpensive chiral diamine ligand enables the three-component cross-coupling of terminal alkynes, a diboron reagent, and prochiral alkyl electrophiles with high levels of regio-, stereo-, and enantioselectivities. This reaction provides an efficient protocol to access enantioenriched alkenyl esters bearing an α-stereogenic center, is remarkably practical, and has a broad scope and an outstanding functional group compatibility. In addition, the value of this method has been highlighted in a diversity of follow-up stereoretentive derivatizations and the stereoselective concise synthesis of complex drug molecules.

Regio- and enantioselective CuH-catalyzed 1,2- and 1,4-hydrosilylation of 1,3-enynes

We report a copper-catalyzed ligand-controlled selective 1,2- and 1,4-hydrosilylation of 1,3-enynes, which furnishes enantiomerically enriched propargyl- and 1,2-allenylsilane products in high yields with excellent enantioselectivities (up to 99% ee). This reaction proceeds under mild conditions, shows broad substrate scope for both 1,3-enynes and trihydrosilanes, and displays excellent regioselectivities. Mechanistic studies based on deuterium-labeling reactions and density functional theory (DFT) calculations suggest that allenylcopper is the dominant reactive intermediate under both 1,2- and 1,4-hydrosilylation conditions, and it undergoes metathesis with silanes via selective four-membered or six-membered transition state, depending on the nature of the ligand. The weak interactions between the ligands and the reacting partners are found to be the key controlling factor for the observed regioselectivity switch. The origin of high enantiocontrol in the 1,4-hydrosilylation is also revealed by high level DLPNO-CCSD(T) calculations.

Nickel-Catalyzed Markovnikov-Selective Hydrodifluoromethylation of Alkynes Using BrCF2 H

A Markovnikov-selective hydrodifluoromethylation of alkynes with BrCF2 H via nickel catalysis is described. This protocol proceeds via a migratory insertion of nickel hydride to alkyne followed by a CF2 H-coupling, enabling straightforward access to diverse branched CF2 H-alkenes with high efficiency and exclusive regioselectivity. The mild condition applies to a wide array of aliphatic and aryl alkynes with good functional group compatibility. Mechanistic studies are presented to support the proposed pathway.

Iron-Catalyzed Alkene Hydroalumination

Hydroalumination of olefins generally gives thermodynamically controlled anti-Markovnikov addition selectivity in literatures. In this paper, a highly Markovnikov hydroalumination of aromatic terminal alkenes was realized to prepare various new benzylaluminum complexes by using the well-defined 2,9-diaryl-1,10-phenanthroline modified iron complex as the catalyst and commercially available DIBAL-H as the aluminum hydride reagent. This is the first ironcatalyzed alkene hydroalumination, and the regioselectivity observed in this study is different from the related reactions reported in the literatures.

Recent Progress in NiH-Catalyzed Linear or Branch Hydrofunctionalization of Terminal or Internal Alkenes

The construction of C-C and C-X (X = N, O, Si, etc.) bonds is an important field in organic synthesis and methodology. In recent decades, studies on transition metal-catalyzed functionalization of alkenes have been on the rise. The individual properties of different transition metals determine the type of reaction that can be applied. Generally, post-transition metals with a large number of electrons in the d-orbit such as Mn, Fe, Co, Ni, Cu and Zn, etc., can be applied to more reaction types than pre-transition metals with a small number of electrons (e.g., Ti, Zr, etc.). Alkyl nickel intermediates formed by oxidative addition could couple with various of nucleophiles or electrophiles. Moreover, nickel has several oxidation valence states, which can flexibly realize a variety of catalytic cycles. These characteristics make nickel favored by researchers in the field of functionalization of alkenes, especially for the hydrofunctionalization of alkenes. Both terminal and internal alkenes could be converted, and the strategies of synthesizing linear and branched compounds have been expanded. Moreover, the guiding groups in alkenes played an almost decisive role in the regional selectivity, and the ligand or temperature also had regulating effects. Herein, we will give a comprehensive and timely overview of the works about the Ni-catalyzed hydrofunctionalization of alkenes and some insights on regional selectivity.