Nickel-Catalyzed Reductive Cross-Coupling Research Articles

Achieving Nickel-Catalyzed Reductive C(sp2)-B Coupling of Bromoboranes via Reversing the Activation Sequence.

Transition metal-catalyzed reductive cross-couplings to build C-C/Si bonds have been developed, but the reductive cross-coupling to create the C(sp2)-B bond has not been explored. Herein, we describe a nickel-catalyzed reductive cross-coupling between aryl halides and bromoboranes to construct a C(sp2)-B bond. This protocol offers a convenient approach for the synthesis of a wide range of aryl boronate esters, using readily available starting materials. Mechanistic studies indicate that the key to the success of the reaction is the activation of the B-Br bond of bromoboranes with a Lewis base such as 2-MeO-py. The activation ensures that bromoboranes will react with the active nickel(I) catalyst prior to aryl halides, which is different from the sequence of the general nickel-catalyzed reductive C(sp2)-C/Si cross-coupling, where the oxidative addition of an aryl halide proceeds first. Notably, this approach minimizes the production of undesired homocoupling byproduct without the requirement of excessive quantities of either substrate.

Nickel-Catalyzed Reductive Cross-Coupling of Propargylic Acetates with Chloro(vinyl)silanes: Access to Silylallenes.

Because of their various reactivities, propargyl acetates are refined chemical intermediates that are extensively applied in pharmaceutical synthesis. Currently, reactions between propargyl acetates and chlorosilanes may be the most effective method for synthesizing silylallenes. Nevertheless, owing to the adaptability and selectivity of substrates, transition metal catalysis is difficult to achieve. Herein, nickel-catalyzed reductive cross-coupling reactions between propargyl acetates and substituted vinyl chlorosilanes for the synthesis of tetrasubstituted silylallenes are described. Therein, metallic zinc is a crucial reductant that effectively enables two electrophilic reagents to selectively construct C(sp2)-Si bonds. Additionally, a Ni-catalyzed reductive mechanism involving a radical process is proposed on the basis of deuteration-labeled experiments.

Nickel-Catalyzed Reductive Arylation of Redox Active Esters for the Synthesis of α-Aryl Nitriles: Investigation of a Chlorosilane Additive.

A nickel-catalyzed reductive cross-coupling of redox active N-hydroxyphthalimide (NHP) esters and iodoarenes for the synthesis of α-aryl nitriles is described. The NHP ester substrate is derived from cyanoacetic acid, which allows for a modular synthesis of substituted α-aryl nitriles, an important scaffold in the pharmaceutical sciences. The reaction exhibits a broad scope, and many functional groups are compatible under the reaction conditions, including complex highly functionalized medicinal agents. Mechanistic studies reveal that reduction and decarboxylation of the NHP ester to the reactive radical intermediate are accomplished by a combination of a chlorosilane additive and Zn dust. We demonstrate that stoichiometric chlorosilane is essential for product formation and that chlorosilane plays a role beyond activation of the metal reductant.

Nickel-Catalyzed Reductive Cross-Coupling of Allylammonium Salts with Alkyl Iodides.

An unprecedented reductive cross-coupling reaction of allylammonium salts with alkyl electrophiles has been established through C-N bond cleavage. A range of allylammonium bromides smoothly participated in the nickel-catalyzed zinc-mediated allyl-alkyl cross-electrophile coupling reaction with alkyl iodides, delivering structurally diverse alkene products in moderate to good yields with high linear selectivity. Preliminary mechanistic experiments are consistent with the formation of an alkyl radical from the alkyl iodide.

Nickel-Catalyzed Reductive Cross-Coupling of Aziridines and Allylic Chlorides.

A nickel-catalyzed reductive cross-coupling of aziridines and allylic chlorides was realized by using manganese metal as the reducing agent. This protocol afforded a convenient approach to obtain β-allyl-substituted arylethylamines bearing various functional groups. The utility of this reaction was also demonstrated by scale-up preparation and diverse transformations, including the synthesis of Baclofen and several bioactive molecular motifs.

Synthesis of Functionalized Skipped Dienes via Nickel-Catalyzed Reductive Cross-Coupling

Key words nickel catalysis - three-component cross-coupling - skipped dienes

Nickel-Catalyzed Reductive Three-Component Cross-Coupling of Butadiene with Aldehydes and Alkenyl Triflates/Bromides: Access to Skipped Dienes

A regio- and stereoselective nickel-catalyzed reductive three-component cross-coupling of 1,3-butadiene with aldehydes and alkenyl triflates or bromides was realized. This protocol afforded a convenient approach to the synthesis of skipped diene compounds bearing various functionals and heterocyclic groups. The utility of this reaction was also demonstrated by scale-up preparation and diverse transformations.

Nickel-Catalyzed Reductive Iminoarylation of Oxime Ester-Tethered Alkenes: Rapid Entrance to Diverse Functionalized Pyrrolines

Herein, we disclose a general and practical iminoarylation of alkenes by nickel-catalyzed reductive cross-coupling of unsaturated oxime esters with readily available aryl halides, providing an expedient approach for constructing pyrroline derivatives. The absence of organometallic reagents enables the reaction to occur under mild conditions with a broad substrate scope and good functional group tolerance. Moreover, other C-based electrophiles, including alkenyl, alkynyl and alkyl halides, or pseudohalides, were also competent substrates for this reaction.

Mechanisms of nickel-catalyzed reductive cross-coupling reactions

Nickel-catalyzed reductive cross-coupling (RCC) reactions using two carbon electrophiles as coupling partners provide one of the most reliable and straightforward protocols for facile construction of valuable C-C bonds in the realm of organic chemistry. In recent years, significant progress has been made in the methodological developments and mechanistic studies of these reactions. This review summarizes four widely accepted mechanisms for RCC reactions that have been proposed by experiments or density functional theory calculations. The major difference between these four types of mechanisms lies in the oxidation state of the active catalyst, the change in the valence of nickel during the catalytic cycle, the involvement of carbon radicals, and the form in which the radicals are present. Herein, we focus on covering representative advancements in experimental and theoretical mechanistic studies, aiming to offer vital mechanistic insights into key intermediates, reaction rates, the activation modes of electrophiles, rate- or selectivity-determining steps, and the origin of the cross-selectivity.

Photoinduced nickel-catalyzed reductive acyl cross-coupling: facile access to all carbon quaternary aliphatic ketones

A photochemical nickel-catalyzed reductive acyl coupling of unstrained tertiary acyl electrophiles with 1°, 2°, and 3°-alkyl radical precursors to synthesize sterically hindered α-tertiary dialkyl ketones is developed.

Nickel-catalyzed reductive coupling of nitroarenes and phosphine oxides to access phosphinic amides

We report a nickel-catalyzed reductive cross-coupling between readily available nitroarenes and phosphine oxides to access phosphinic amides.

Picolinamide Ligands: Nickel-Catalyzed Reductive Cross-Coupling of Aryl Bromides with Bromocyclopropane and Beyond.

The arylcyclopropane motif as the combination of aryl and cyclopropyl ring systems can be found in an increasing amount of approved and investigational drugs. Herein, we have developed a mild, efficient nickel-catalyzed reductive cross-coupling protocol, featuring a simple Ni(II) precatalyst and a novel picolinamide NN2 pincer ligand. A variety of (hetero)aryl bromides could successfully couple with cyclopropyl bromide to furnish the valued arylcyclopropanes in good to excellent yields. This method is applicable to other alkyl bromides as well. Notably, the reaction is tolerant of a broad range of functionalities including free amines. Furthermore, the synthesis of several significant intermediates of bioactive molecules was achieved in grams, proving the practicability of this method.

Ni-Catalyzed Reductive Cross-Coupling of Cyclopropylamines and Other Strained Ring NHP Esters with (Hetero)Aryl Halides.

A nickel-catalyzed reductive cross-coupling of cyclopropylamine NHP esters with (hetero)aryl halides is reported. This efficient protocol provides direct access to 1-arylcyclopropylamines, a bioisosteric motif commonly used in small molecule drug discovery. The reaction proceeds rapidly (<2 h) with excellent functional group tolerance and without requiring heat- or air-sensitive reagents. The method can also be extended to the arylation of four-membered strained rings. The NHP esters are easily obtained from the corresponding commercially available carboxylic acids in one step with high yields and no column chromatography.

Desymmetrization of Malononitriles by Intramolecular Nickel-Catalyzed Reductive Cross-Coupling

Key words reductive cross-coupling - malononitriles - nickel catalysis - Phox ligands - desymmetrization - all-carbon quaternary stereocenters

Nickel-Catalyzed Reductive Cross-Coupling of (Hetero)Aryl Bromides with Vinyl Acetate

Nickel-Catalyzed Reductive Cross-Coupling of (Hetero)Aryl Bromides with Vinyl Acetate

Nickel-Catalyzed Reductive Cross-Coupling of Oxalates Derived from α-Hydroxy Carbonyls with Vinyl Bromides

AbstractA nickel-catalyzed cross-electrophile coupling is disclosed in which a range of vinyl bromides were utilized as electrophiles with oxalates derived from α-hydroxy carbonyls as precursors to carbonyl radical coupling partners. This method is compatible with a broad range of functional groups, providing a complementary solution for the construction of β,γ-unsaturated carbonyl compounds.

Nickel-catalyzed reductive cross-coupling of polyfluoroarenes with alkyl electrophiles by site-selective C–F bond activation

A nickel-catalyzed reductive cross-coupling reactions between polyfluoroarenes and alkyl electrophiles is reported to access substituted fluoroarenes through chelation-assisted C–F activation. Diverse primary and secondary alkyl (pseudo)halides can be employed to couple with polyfluoroarenes, showing excellent regioselectivity. Furthermore, the nickel-catalyzed asymmetric cross-coupling of polyfluoroarenes with racemic alkyl halides is preliminarily explored. In addition, the practicability of the title transformation is also demonstrated by total synthesis of losmapimod and an analog as key steps. The developed method exhibits many advantages, including economic catalytic systems, commercially available alkyl electrophiles, and lack of sensitive organometallic reagents.

Nickel-Catalyzed Reductive Cross-Coupling of Benzylic Sulfonium Salts with Aryl Iodides

A nickel-catalyzed cross-electrophile coupling of benzylic sulfonium salts with aryl iodides has been developed, providing direct access to diarylalkanes from readily available and stable coupling partners. Preliminary mechanistic studies suggest that the C–S bond cleavage proceeds through a single-electron transfer process to generate a benzylic radical.

Construction of diverse C–S/C–Se bonds via nickel catalyzed reductive coupling employing thiosulfonates and a selenosulfonate under mild conditions

A nickel-catalyzed reductive cross coupling between organic iodides and thiosulfonates and a selenosulfonate under mild conditions is disclosed.

Photoredox Nickel-Catalyzed Asymmetric Reductive Cross Coupling

Photoredox Nickel-Catalyzed Asymmetric Reductive Cross Coupling