Nickel-Catalyzed Regio- and Enantioselective Hydroamination of Unactivated Alkenes Using Carbonyl Directing Groups

Nickel-Catalyzed, Aminoquinoline-Directed Chemo- and Regioselective Carboamination of Unactivated Olefins with Organoboronic Acids and Anthranils

A nickel-catalyzed three-component carboamination of unactivated alkenes with organoboronic acids and anthranils has been achieved for the expedient synthesis of δ-aryl and γ-amino acid derivatives. The 8-aminoquinoline (AQ) directing group is crucial for the success of the reaction, and anthranil serves as an arylnitrene precursor in this conversion. This method features mild reaction conditions, good chemo- and regioselectivity, and a broad substrate scope with good functional group tolerance.

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.

Nickel Catalyzed Enantioselective 1,4-Hydroamination of 1,3-Dienes

Transition metal-catalyzed enantioselective hydroamination of 1,3-dienes provides a direct methodology for the construction of chiral allylamines. So far, all of the reported examples used nucleophilic amines and proceeded with 3,4-regioselectivity. Herein, we describe the first example of nickel-catalyzed enantioselective 1,4-hydroamination of 1,3-dienes using trimethoxysilane and hydroxylamines with a structurally adaptable aromatic spiroketal based chiral diphosphine (SKP) as the ligand, affording a wide array of α-substituted chiral allylamines in high yields with excellent regio- and enantioselectivities. This operationally simple protocol demonstrated a broad substrate scope and excellent functional group compatibility, significantly expanding the chemical space for chiral allylamines. Experimental and DFT studies were performed to elucidate the mechanism and to rationalize the regio- and enantioselectivities of the reaction.

Enantioselective Ni-Catalyzed 1,2-Borylalkynylation of Unactivated Alkenes

Enantioselective three-component difunctionalization of alkenes with boron reagents represents an attractive strategy for assembling three-dimensional chiral organoboron compounds. However, regio- and enantiocontrol comprise the pivot challenges in these transformations, which predominantly require the use of activated conjugated alkenes. Herein, by utilizing various carbonyl directing groups, including amides, sulfinamides, ketones, and esters, we succeed in realizing a nickel-catalyzed 1,2-borylalkynylation of unactivated alkenes to enable the simultaneous incorporation of a boron entity and an sp-fragment across the double bond. The products contain boryl, alkynyl, and carbonyl functional groups with orthogonal synthetic reactivities, offering three handles for further derivatization to access valuable intermediates. The utility of this ligand-enabled asymmetric protocol has been highlighted through the late-stage decoration of drug-relevant molecules.

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.

Triflic Acid-Promoted 1,2-Amino Migration Reactions in α-Arylaminoacrylamides: Access to Substituted β-Aminoamides

A straightforward synthesis of substituted β-aminoamides from α-arylamino-β-hydroxyacrylamides, α-arylamino-β-oxoamides, or their tautomeric mixture has been described. The (E)-enol triflate intermediates are readily generated in situ from these substrates in the presence of triflic anhydride (Tf2O) and triethylamine (Et3N) in a chemoselective manner and undergo triflic acid (TfOH)-promoted cyclization and ring-opening reactions with alcohols to deliver the desired products. The one-pot two-step synthetic protocol features the use of readily available starting materials, mild reaction conditions, high chemoselectivity, operational simplicity, and a wide range of synthetic potential of the products.

Nickel-catalysed regio- and stereoselective hydrocyanation of alkynoates and its mechanistic insights proposed by DFT calculations

We have developed a nickel-catalysed regio- and stereoselective hydrocyanation of alkynoates that gives syn-β-cyanoalkenes. DFT calculations suggest that a favored transition state promotes Cα-H bond formation for determining regio- and stereoselectivity of the products.

Nickel-Catalyzed Hydrofluorination in Unactivated Alkenes: Regio- and Enantioselective C-F Bond Formation

Catalytic formation of a regio- and enantioselective C-F bond chiral center from readily available alkenes is a crucial goal, yet it continues to pose significant challenges in organic synthesis. Here, we report the regioselective formation of C-F bonds facilitated by NiH catalysis and a coordination directing strategy that enables precise hydrofluorination of both terminal and internal alkenes. Notably, we have optimized this methodology to achieve high enantioselectivity in creating aliphatic C-F stereogenic centers especially with β,γ-alkenyl substrates, using a tailored chiral Bn-BOx ligand. Another pivotal finding in our research is the identification of the (+)-nonlinear effect under optimized conditions, allowing for high enantioselectivity even with moderately enantiomerically enriched chiral ligands. Given the significant role of fluorine in pharmaceuticals and synthetic materials, this research offers essential insights into the regioselective and enantioselective formation of C-F bond chiral centers, paving the way for the efficient production of valuable fluorinated compounds.

Rhodium-Catalyzed Asymmetric Macrocyclization towards Crown Ethers Using Hydroamination of Bis(allenes)

Enantiomerically enriched crown ethers (CE) exhibit strong asymmetric induction in phase transfer catalysis, supramolecular catalysis and molecular recognition processes. Traditional methods have often been used to access these valuable compounds, which limit their diversity and consequently their applicability. Herein, a practical catalytic method is described for the gram scale synthesis of a class of chiral CEs (aza-crown ethers; ACEs) using Rh-catalyzed hydroamination of bis(allenes) with diamines. Using this approach, a wide range of chiral vinyl functionalized CEs with ring sizes ranging from 12 to 36 have been successfully prepared in high yields of up to 92 %, dr of up to >20 : 1 and er of up to >99 : 1. These vinyl substituted CEs allow for further diversification giving facile access to various CE derivatives as well as to their three-dimensional analogues using ring-closing metathesis. Some of these chiral CEs themselves display high potential for use in asymmetric catalysis.

NiH-catalyzed C-N bond formation: insights and advancements in hydroamination of unsaturated hydrocarbons

The formation of C-N bonds is a fundamental aspect of organic synthesis, and hydroamination has emerged as a pivotal strategy for the synthesis of essential amine derivatives. In recent years, there has been a surge of interest in metal hydride-catalyzed hydroamination reactions of common alkenes and alkynes. This method avoids the need for stoichiometric organometallic reagents and overcomes problems associated with specific organometallic compounds that may impact functional group compatibility. Notably, recent developments have brought to the forefront olefinic hydroamination and hydroamidation reactions facilitated by nickel hydride (NiH) catalysis. The inclusion of suitable chiral ligands has paved the way for the realization of asymmetric hydroamination reactions in the realm of olefins. This review aims to provide an in-depth exploration of the latest achievements in C-N bond formation through intermolecular hydroamination catalyzed by nickel hydrides. Leveraging this innovative approach, a diverse range of alkene and alkyne substrates can be efficiently transformed into value-added compounds enriched with C-N bonds. The intricacies of C-N bond formation are succinctly elucidated, offering a concise overview of the underlying reaction mechanisms. It is our aspiration that this comprehensive review will stimulate further progress in NiH-catalytic techniques, fine-tune reaction systems, drive innovation in catalyst design, and foster a deeper understanding of the underlying mechanisms.

Ligand-modulated nickel-catalyzed regioselective silylalkylation of alkenes

Organosilicon compounds have shown tremendous potential in drug discovery and their synthesis stimulates wide interest. Multicomponent cross-coupling of alkenes with silicon reagents is used to yield complex silicon-containing compounds from readily accessible feedstock chemicals but the reaction with simple alkenes remains challenging. Here, we report a regioselective silylalkylation of simple alkenes, which is enabled by using a stable Ni(II) salt and an inexpensive trans-1,2-diaminocyclohexane ligand as a catalyst. Remarkably, this reaction can tolerate a broad range of olefins bearing various functional groups, including alcohol, ester, amides and ethers, thus it allows for the efficient and selective assembly of a diverse range of bifunctional organosilicon building blocks from terminal alkenes, alkyl halides and the Suginome reagent. Moreover, an expedient synthetic route toward alpha-Lipoic acid has been developed by this methodology.

Nickel/SKP-Catalyzed Markovnikov Regio- and Enantioselective Hydroamination of Vinylarenes with Hydroxylamines

A Ni-catalyzed enantioselective hydroamination of vinylarenes has been developed, affording a wide variety of α-branched chiral alkylamines in good yields with exclusive Markovnikov regioselectivity and excellent enantioselectivity. The SKP ligand was found to be crucial to both the reactivity enhancement and enantiocontrol of the reaction. The synthetic utility of the protocol was exemplified in a gram-scale reaction and late-stage modification of medicinally relevant molecules. The deuterium-labeling experiment revealed that the irreversible hydronickelation of vinylarenes is most likely the enantioselectivity-determining step.

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.

Electrocatalytic Access to Azetidines via Intramolecular Allylic Hydroamination: Scrutinizing Key Oxidation Steps through Electrochemical Kinetic Analysis

Azetidines are prominent structural scaffolds in bioactive molecules, medicinal chemistry, and ligand design for transition metals. However, state-of-the-art methods cannot be applied to intramolecular hydroamination of allylic amine derivatives despite their underlying potential as one of the most prevalent synthetic precursors to azetidines. Herein, we report an electrocatalytic method for intramolecular hydroamination of allylic sulfonamides to access azetidines for the first time. The merger of cobalt catalysis and electricity enables the regioselective generation of key carbocationic intermediates, which could directly undergo intramolecular C-N bond formation. The mechanistic investigations including electrochemical kinetic analysis suggest that either the catalyst regeneration by nucleophilic cyclization or the second electrochemical oxidation to access the carbocationic intermediate is involved in the rate-determining step (RDS) of our electrochemical protocol and highlight the ability of electrochemistry in providing ideal means to mediate catalyst oxidation.

Progression of Hydroamination Catalyzed by Late Transition-Metal Complexes from Activated to Unactivated Alkenes

ConspectusCatalytic intermolecular hydroamination of alkenes is an atom- and step-economical method for the synthesis of amines, which have important applications as pharmaceuticals, agrochemicals, catalysts, and materials. However, hydroaminations of alkenes in high yield with high selectivity are challenging to achieve because these reactions often lack a thermodynamic driving force and often are accompanied by side reactions, such as alkene isomerization, telomerization, and oxidative amination. Consequently, early examples of hydroamination were generally limited to the additions of N-H bonds to conjugated alkenes or strained alkenes, and the catalytic hydroamination of unactivated alkenes with late transition metals has only been disclosed recently. Many classes of catalysts, including early transition metals, late transition metals, rare-earth metals, acids, and photocatalysts, have been reported for catalytic hydroamination. Among them, late transition-metal complexes possess several advantages, including their relative ease of handling and their high compatibility of substrates containing polar or sensitive functional groups.This Account describes the progression in our laboratory of hydroaminations catalyzed by late transition-metal complexes from the initial additions of N-H bonds to activated alkenes to the more recent additions to unactivated alkenes. Our developments include the Markovnikov and anti-Markovnikov hydroamination of vinylarenes with palladium, rhodium, and ruthenium, the hydroamination of dienes and trienes with nickel and palladium, the hydroanimation of bicyclic strained alkenes with neutral iridium, and the hydroamination of unactivated terminal and internal alkenes with cationic iridium and ruthenium. Enantioselective hydroaminations of these classes of alkenes to form enantioenriched, chiral amines also have been developed.Mechanistic studies have elucidated the elementary steps and the turnover-limiting steps of these catalytic reactions. The hydroamination of conjugated alkenes catalyzed by palladium, rhodium, nickel, and ruthenium occurs by turnover-limiting nucleophilic attack of the amine on a coordinated benzyl, allyl, alkene, or arene ligand. On the other hand, the hydroamination of unconjugated alkenes catalyzed by ruthenium and iridium occurs by turnover-limiting migratory insertion of the alkene into a metal-nitrogen bond. In addition, pathways for the formation of side products, including isomeric alkenes and enamines, have been identified during our studies. During studies on enantioselective hydroamination, the reversibility of the hydroamination has been shown to erode the enantiopurity of the products. Based on our mechanistic understandings, new generations of catalysts that promote catalytic hydroaminations with higher rates, chemoselectivity, and enantioselectivity have been developed. We hope that our discoveries and mechanistic insights will facilitate the further development of catalysts that promote selective, practical, and efficient hydroamination of alkenes.

Nickel-Catalyzed Remote Asymmetric Hydroalkylation of Alkenyl Ethers to Access Ethers of Chiral Dialkyl Carbinols

Site- and enantio-selective alkyl-alkyl bond formation is privileged in the retrosynthetic analysis due to the universality of sp³-hybridized carbon atoms in organic molecules. Herein, we report a nickel-catalyzed remote asymmetric hydroalkylation of alkenyl ethers via synchronous implementation of alkene isomerization and enantioselective C(sp³)-C(sp³) bond formation. Regression analysis of catalyst structure-activity relationships accelerates the rational ligand modification through modular regulation. This reaction has several advantages for synthesizing chiral dialkyl carbinols and their ether derivatives, including the broad substrate scope, good functional group tolerance, excellent regioselectivity (>20:1 regioisomeric ratio), and high enantioselectivity (up to 95% enantiomeric excess).

Regio- and chemoselective hydroamination of unactivated alkenes with anthranils via NiH-catalysis

A NiH-catalyzed polarity-reversed hydroamination of β,γ-, γ,δ- and δ,ε-unsaturated alkenes with electrophilic anthranils was developed. This reaction proceeds in a highly regio- and chemoselective manner to afford γ, δ and ε-arylamines bearing a carbonyl or alcohol functionality with 100% atom efficiency. Preliminary mechanistic studies indicate that the chemoselectivity is controlled by the base and the alcohol product is derived from the base-catalyzed hydrosilylation of the CO bond.

Cobalt-Catalyzed Enantioselective Hydroamination of Arylalkenes with Secondary Amines

Catalytic asymmetric hydroamination of alkenes with Lewis basic amines is of great interest but remains a challenge in synthetic chemistry. Here, we developed a Co-catalyzed asymmetric hydroamination of arylalkenes directly using commercially accessible secondary amines. This process enables the efficient access to valuable α-chiral tertiary amines in good to excellent yields and enantioselectivities. Mechanistic studies suggest that the reaction includes a CoH-mediated hydrogen atom transfer (MHAT) with arylalkenes, followed by a pivotal catalyst controlled S_N 2-like pathway between in situ generated electrophilic cationic alkylcobalt(IV) species and free amines. This radical-polar crossover strategy not only provides a straightforward and alternative approach for the synthesis of enantioenriched α-tertiary amines, but also underpins the substantial opportunities in developing asymmetric radical functionalization of alkenes with various free nucleophiles in oxidative MHAT catalysis.

NiH-Catalyzed Proximal-Selective Hydroamination of Unactivated Alkenes with Anthranils

The regioselective hydroamination of unactivated alkenes is a long-standing challenge in organic synthesis. Herein, we report a NiH-catalyzed proximal-selective hydroamination of unactivated alkenes with 8-aminoquinoline (AQ) as a bidentate auxiliary and anthranils as aminating reagents. A wide range of primary aryl amines bearing an ortho-carbonyl group were installed in both terminal and internal unactivated alkenes, delivering a variety of valuable β- and γ-amino acid building blocks, respectively, with excellent regiocontrol. The utility of this transformation was further demonstrated by the conversion of the multifunctionalized aryl amines into useful N-heterocycles.

Remote and Proximal Hydroaminoalkylation of Alkenes Enabled by Photoredox/Nickel Dual Catalysis

A mild and site-selective hydroaminoalkylation of activated and unactivated alkenes via dual photoredox/Ni catalysis is developed. This dual catalytic strategy enables exclusive access to α-selective products, which is complementary to previously reported photocatalytic hydroaminoalkylation of activated alkenes that provides the β-selective products. The chain-walking of a Ni-H intermediate toward a carbonyl allows for the hydroaminoalkylation of unactivated alkenes at remote sp³ C-H sites. This method tolerates a broad substrate scope of both amines and alkenes as well as providing a streamlined synthesis of value-added β-amino acid derivatives from readily available starting materials.

Exogenous Ligand-Free NiH-Catalyzed Hydroacylation of Aryl Alkenes with Aroyl Fluorides

Acyl fluorides have emerged as efficient acyl group donors, but these attractive reagents have rarely been utilized in transition-metal-catalyzed hydroacylation. Herein we report a nickel hydride-catalyzed hydroacylation of aryl alkenes using aroyl fluorides. The reaction proceeds without recourse to an exogenous ligand under mild conditions. The synthetic utility of the present method is demonstrated by the glovebox-free, gram-scale reaction and the late-stage derivatization of complex molecules containing pharmaceutical frameworks.