Nickel-Catalyzed Reductive Arylalkylation via a Migratory Insertion/Decarboxylative Cross-Coupling Cascade

Cross-Electrophile Coupling: Principles, Methods, and Applications in Synthesis

Cross-electrophile coupling (XEC), defined by us as the cross-coupling of two different σ-electrophiles that is driven by catalyst reduction, has seen rapid progression in recent years. As such, this review aims to summarize the field from its beginnings up until mid-2023 and to provide comprehensive coverage on synthetic methods and current state of mechanistic understanding. Chapters are split by type of bond formed, which include C(sp3)-C(sp3), C(sp2)-C(sp2), C(sp2)-C(sp3), and C(sp2)-C(sp) bond formation. Additional chapters include alkene difunctionalization, alkyne difunctionalization, and formation of carbon-heteroatom bonds. Each chapter is generally organized with an initial summary of mechanisms followed by detailed figures and notes on methodological developments and ending with application notes in synthesis. While XEC is becoming an increasingly utilized approach in synthesis, its early stage of development means that optimal catalysts, ligands, additives, and reductants are still in flux. This review has collected data on these and various other aspects of the reactions to capture the state of the field. Finally, the data collected on the papers in this review is offered as Supporting Information for readers.

Ligand-Controlled, Nickel-Catalyzed Stereodivergent Construction of 1,3-Nonadjacent Stereocenters

In contrast to the asymmetric synthesis of molecules with a single stereocenter or 1,2-adjacent stereocenters, the simultaneous construction of acyclic 1,3-nonadjacent stereocenters via a single catalyst in an enantioselective and diastereoselective manner remains a formidable challenge. Here, we demonstrate the enantioselective and diastereodivergent construction of 1,3-nonadjacent stereocenters through Ni-catalyzed reductive cyclization/cross-coupling of alkene-tethered aryl bromides and α-bromoamides, which represents the major remaining stereochemical challenge of cyclization/difunctionalization of alkenes. Using Ming-Phos as ligand, a diverse set of oxindoles containing 1,3-nonadjacent stereocenters were obtained with high levels of enantio- and diastereoselectivity. Mechanistic experiments and density functional theory calculations indicate that magnesium salt plays a key role in controlling the diastereoselectivity. Furthermore, another set of complementary stereoisomeric products were constructed from the same set of starting materials using Ph-Phox as ligand.

Nickel Nanoparticles for Liquid Phase Toluene Oxidation – Phenomenon, Opportunities and Challenges

Effective oxidative transformation of toluene into valuable products was achieved under solvent‐free reaction conditions with as‐prepared nickel nanoparticles as heterogeneous catalysts in liquid phase. The crystalline structure and size of the as‐prepared nanoparticles were confirmed by X‐ray diffractometry (XRD) and dynamic light scattering (DLS). The catalytic implications of the different crystalline forms (face‐centred cubic: fcc; hexagonal close‐packed: hcp) of these nanocatalysts were investigated. The product selectivity of toluene oxidation was found to vary depending on the crystalline forms of the catalyst. Fcc nanocatalysts showed remarkable chemoselectivity (83 mol %) for the product benzyl alcohol and were readily reusable. In contrast, the hcp Ni phase showed reasonable reusability but lower chemoselectivity (29 mol %) compared to its fcc counterpart. Moreover, the simple organic solvents used had a remarkable effect on the crystal structure and phase purity of the Ni nanocrystals, which also affected the catalytic process.

Nickel-Catalyzed Enantioselective Reductive Alkyl-Carbamoylation of Internal Alkenes

Herein, we leverage the Ni-catalyzed enantioselective reductive dicarbofunctionalization of internal alkenes with alkyl iodides to enable the synthesis of chiral pyrrolidinones bearing vicinal stereogenic centers. The application of newly developed 1-Nap Quinim is critical for formation of two contiguous stereocenters in high yield, enantioselectivity, and diastereoselectivity. This catalytic system also improves both the yield and enantioselectivity in the synthesis of α,α-dialkylated γ-lactams. Computational studies reveal that the enantiodetermining step proceeds with a carbamoyl-NiI intermediate that is reduced by the Mn reductant prior to intramolecular migratory insertion. The presence of the t-butyl group of the Quinim ligand leads to an unfavorable distortion of the substrate in the TS that leads to the minor enantiomer. Calculations also support an improvement in enantioselectivity with 1-Nap Quinim compared to p-tol Quinim.

Nickel-Catalyzed Reductive Cascade Arylalkylation of Alkenes with Alkylpyridinium Salts

Herein, we describe a nickel-catalyzed reductive deaminative arylalkylation of tethered alkenes with pyridinium salts as C(sp³) electrophiles. This two-component dicarbofunctionalization reaction enables the efficient synthesis of various benzene-fused cyclic compounds bearing all-carbon quaternary centers. The approach presented in this paper proceeds under mild conditions, tolerating a wide variety of functional groups and heterocycles. It has been used to functionalize complicated molecules at a late stage.

Density Functional Theory Study of Gold-Catalyzed 1,2-Diarylation of Alkenes: π-Activation versus Migratory Insertion Mechanisms

Density functional theory calculations are carried out to better understand the first gold-catalyzed 1,2-diarylation reactions of alkenes reported in the recent literature. The calculations on two representative reactions, aryl alkene/aryl iodide coupling pair (the aryl-I bond is located outside the aryl alkene) versus iodoaryl alkene/indole coupling pair (the aryl-I bond is located in the aryl alkene), confirm that the reaction involves a π-activation mechanism rather than the general migratory insertion mechanism in previously known metal catalysis by Pd, Ni, and Cu complexes. Theoretical results rationalize the regioselectivity of the reactions controlled by the aryl-I bond position (intermolecular or intramolecular) and also the ligand and substituent effects on the reactivity.

Nickel-Catalyzed Asymmetric Reductive Dicarbamoylation of Alkenes

Herein we report a nickel-catalyzed asymmetric reductive dicarbamoylation of alkenes, in which tethered carbamoyl chlorides and isocyanates serve as distinct electrophilic carbamoylating agents, providing new access to chiral oxindoles bearing an amide-substituted quaternary stereogenic center.

Photoactive electron donor-acceptor complex platform for Ni-mediated C(sp3)-C(sp2) bond formation

A dual photochemical/nickel-mediated decarboxylative strategy for the assembly of C(sp3)-C(sp2) linkages is disclosed. Under light irradiation at 390 nm, commercially available and inexpensive Hantzsch ester (HE) functions as a potent organic photoreductant to deliver catalytically active Ni(0) species through single-electron transfer (SET) manifolds. As part of its dual role, the Hantzsch ester effects a decarboxylative-based radical generation through electron donor-acceptor (EDA) complex activation. This homogeneous, net-reductive platform bypasses the need for exogenous photocatalysts, stoichiometric metal reductants, and additives. Under this cross-electrophile paradigm, the coupling of diverse C(sp3)-centered radical architectures (including primary, secondary, stabilized benzylic, α-oxy, and α-amino systems) with (hetero)aryl bromides has been accomplished. The protocol proceeds under mild reaction conditions in the presence of sensitive functional groups and pharmaceutically relevant cores.

Nickel-Catalyzed Dicarbofunctionalization of Alkenes

1,2-Dicarbofunctionalization of alkenes has emerged as an efficient synthetic strategy for preparing substituted molecules by coupling readily available alkenes with electrophiles and/or nucleophiles. Nickel complexes serve as effective catalysts owing to their tendency to undergo facile oxidative addition and slow β-hydride elimination, and their capability to access both two-electron and radical pathways. Two-component alkene functionalization reactions have achieved high chemo-, regio-, and stereoselectivities by tethering one of the coupling partners to the alkene substrate. Three-component reactions, however, often incorporate directing groups to control the selectivity. Only a few examples of directing-group-free difunctionalizations of unactivated alkenes have been reported. Therefore, great opportunities exist for the development of three-component difunctionalization reactions with broad substrate scopes and tunable chemo-, regio-, and stereoselectivities.

Nickel-Catalyzed α-Carbonylalkylarylation of Vinylarenes: Expedient Access to γ,γ-Diarylcarbonyl and Aryltetralone Derivatives

We report a Ni-catalyzed regioselective α-carbonylalkylarylation of vinylarenes with α-halocarbonyl compounds and arylzinc reagents. The reaction works with primary, secondary, and tertiary α-halocarbonyl molecules, and electronically varied arylzinc reagents. The reaction generates γ,γ-diarylcarbonyl derivatives with α-secondary, tertiary, and quaternary carbon centers. The products can be readily converted to aryltetralones, including a precursor to Zoloft, an antidepressant drug.

Nickel-catalyzed enantioselective reductive carbo-acylation of alkenes

Recently, transition-metal-catalyzed asymmetric dicarbofunctionalization of tethered alkenes has emerged as a powerful method for construction of chiral cyclic carbo- and heterocycles. However, all these reactions rely on facially selective arylmetalation of the pendant olefinic unit. Here, we successfully apply acylnickelation as the enantiodetermining step in the asymmetric nickel-catalyzed reductive carbo-acylation of aryl carbamic chloride-tethered alkenes with primary and secondary alkyl iodides as well as benzyl chlorides as the coupling partners, using manganese as a reducing agent. By circumventing the use of pre-generated organometallics, this reductive strategy enables the synthesis of diverse enantioenriched oxindoles bearing a quaternary stereogenic center under mild reaction conditions with high tolerance of a broad range of functional moieties.

Photocatalytic decarboxylative [2 + 2 + 1] annulation of 1,6-enynes with N-hydroxyphthalimide esters for the synthesis of indene-containing polycyclic compounds

An efficient photoredox-mediated [2 + 2 + 1] annulation of 1,6-enynes with N-hydroxyphthalimide esters was reported for the synthesis of spiro and non-spiro indene-containing polycyclic frameworks.