Catalytic Regioselective Olefin Hydroarylation(alkenylation) by Sequential Carbonickelation-Hydride Transfer

Selective 1,2-Hydroarylation(Alkenylation) of gem-Difluoroalkenes to Access (-CF2 H) Motifs

An emerging class of C-C coupling transformations that furnish drug-like building blocks involves catalytic hydrocarbonation of alkenes. However, despite notable advances in the field, hydrocarbon addition to gem-difluoroalkenes without additional electronic activation remains largely unsuccessful. This owes partly to poor reactivity and the propensity of difluoroalkenes to undergo defluorinative side reactions. Here, we report a nickel catalytic system that promotes efficient 1,2-selective hydroarylation and hydroalkenylation, suppressing defluorination and providing straightforward access to a diverse assortment of prized organofluorides bearing difluoromethyl-substituted carbon centers. In contrast to radical-based pathways and reactions triggered by hydrometallation via a nickel-hydride complex, our experimental and computational studies support a mechanism in which a catalytically active nickel-bromide species promotes selective carbonickelation with difluoroalkenes followed by alkoxide exchange and hydride transfer, effectively overcoming the difluoroalkene's intrinsic electronic bias.

Diphosphine Ligand-Enabled Nickel-Catalyzed Chelate-Assisted Inner-Selective Migratory Hydroarylation of Alkenes

The precise control of the regioselectivity in the transition metal-catalyzed migratory hydrofunctionalization of alkenes remains a big challenge. With a transient ketimine directing group, the nickel-catalyzed migratory β-selective hydroarylation and hydroalkenylation of alkenyl ketones has been realized with aryl boronic acids using alkyl halide as the mild hydride source for the first time. The key to this success is the use of a diphosphine ligand, which is capable of the generation of a Ni(II)-H species in the presence of alkyl bromide, and enabling the efficient migratory insertion of alkene into Ni(II)-H species and the sequent rapid chain walking process. The present approach diminishes organosilanes reductant, tolerates a wide array of complex functionalities with excellent regioselective control. Moreover, this catalytic system could also be applied to the migratory hydroarylation of alkenyl azahetereoarenes, thus providing a general approach for the preparation of 1,2-aryl heteroaryl motifs with wide potential applications in pharmaceutical discovery.

Divergent and Selective Light Alkene Cross-Coupling

Light olefins are abundantly manufactured in the petroleum industry and thus represent ideal starting materials for modern chemical synthesis. Selective and divergent transformations of feedstock light olefins to value-added chemicals are highly sought-after but remain challenging. Herein we report an exceptionally regioselective carbonickelation of light alkenes followed by in situ trapping with three types of nucleophiles, namely a reductant, base, or Grignard reagent. This protocol enables efficient 1,2-hydrofunctionalization, dicarbofunctionalization, and branched-selective Heck-type cross-coupling of light alkenes with aryl and alkenyl reagents to streamline access to diverse alkyl arenes and complex alkenes. Harnessing bulky N-heterocyclic carbene ligands with acenaphthyl backbones for nickel catalysts is crucial to attain high reactivity and selectivity. This strategy provides a rare, modular, and divergent platform for upgrading feedstock alkenes and is expected to find broad applications in medicinal chemistry and industrial processes.

Photoinduced Cobalt Catalysis for the Reductive Coupling of Pyridines and Dienes Enabled by Paired Single-Electron Transfer

Selective hydroarylation of dienes has potential to provide swift access to useful building blocks. However, most existing methods rely on dienes stabilised by an aromatic group and transmetallation or nucleophilic attack steps require electron-rich aryl coupling partners. As such, there are few examples which tolerate wide-spread heteroarenes such as pyridine. Whilst allylic C-H functionalisation could be considered an alternative approach, the positional selectivity of unsymmetrical substrates is hard to control. Here, we report a general approach for selective hydropyridylation of dienes under mild conditions using metal catalysed hydrogen-atom transfer. Photoinduced, reductive conditions enable simultaneous formation of a cobalt-hydride catalyst and the persistent radical of easily-synthesised pyridyl phosphonium salts. This facilitates selective coupling of dienes in a traceless manner at the C4-position of a wide-range of pyridine substrates. The mildness of the method is underscored by its functional-group tolerance and demonstrated by applications in late-stage functionalisation. Based on a combination of experimental and computational studies, we propose a mechanistic pathway which proceeds through non-reversible hydrogen-atom transfer (HAT) from a cobalt hydride species which is uniquely selective for dienes in the presence of other olefins due to a much higher relative barrier associated with olefin HAT.

Nickel-Catalyzed Hydroamination and Hydroalkoxylation of Enelactams with Unactivated Amines and Alcohols

Nickel-catalyzed hydroamination and hydroalkoxylation of enelactams with unactivated amines and alcohols are reported. This method showed good functional group tolerance and delivered the corresponding hydrofunctionalized products in good to excellent yields (≤98%). Furthermore, an intramolecular hydroalkoxylation of an enelactam was also realized, giving a cyclization product in a good yield. Mechanistic studies indicated that tBuI acts as a hydride donor and radical precursor, which is crucial for the success of the reaction.

Ligand-enabled Ni-catalyzed hydroarylation and hydroalkenylation of internal alkenes with organoborons

The transition metal-catalyzed hydrofunctionalization of alkenes offers an efficient solution for the rapid construction of complex functional molecules, and significant progress has been made during last decades. However, the hydrofunctionalization of internal alkenes remains a significant challenge due to low reactivity and the difficulties of controlling the regioselectivity. Here, we report the hydroarylation and hydroalkenylation of internal alkenes lacking a directing group with aryl and alkenyl boronic acids in the presence of a nickel catalyst, featuring a broad substrate scope and wide functional group tolerance under redox-neutral conditions. The key to achieving this reaction is the identification of a bulky 1-adamantyl β-diketone ligand, which is capable of overcoming the low reactivity of internal 1,2-disubstituted alkenes. Preliminary mechanistic studies unveiled that this reaction undergoes an Ar-Ni(II)-H initiated hydroarylation process, which is generated by the oxidative addition of alcoholic solvent with Ni(0) species and sequential transmetalation. In addition, the oxidative addition of the alcoholic solvent proves to be the turnover-limiting step.

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.

NiH-catalysed proximal-selective hydroalkylation of unactivated alkenes and the ligand effects on regioselectivity

Alkene hydrocarbonation reactions have been developed to supplement traditional electrophile-nucleophile cross-coupling reactions. The branch-selective hydroalkylation method applied to a broad range of unactivated alkenes remains challenging. Herein, we report a NiH-catalysed proximal-selective hydroalkylation of unactivated alkenes to access β- or γ-branched alkyl carboxylic acids and β-, γ- or δ-branched alkyl amines. A broad range of alkyl iodides and bromides with different functional groups can be installed with excellent regiocontrol and availability for site-selective late-stage functionalization of biorelevant molecules. Under modified reaction conditions with NiCl₂(PPh₃)₂ as the catalyst, migratory hydroalkylation takes place to provide β- (rather than γ-) branched products. The keys to success are the use of aminoquinoline and picolinamide as suitable directing groups and combined experimental and computational studies of ligand effects on the regioselectivity and detailed reaction mechanisms.

Difunctionalization of olefins is an ongoing and important focus of synthetic organic chemistry. Here the authors report a nickel-catalysed hydroalkylation of unactivated alkenes to obtain branched alkyl carboxylic acids or alkyl amines, using aminoquinoline and picolinamide as directing groups.

Nickel-Catalyzed Hydroarylation Reaction: A Useful Tool in Organic Synthesis

This article describes the recent advances in the field of nickel-catalyzed hydroarylation reaction of alkenes, alkynes, and arenes. All reactions proceeded either through internal hydride transfer or in presence of...

Divergent Aminocarbonylations of Alkynes Enabled by Photoredox/Nickel Dual Catalysis

A metallaphotoredox-catalyzed strategy for the selective and divergent aminocarbonylation of alkynes with amines and 1 atm of CO is reported. This synergistic protocol not only enables the Markovnikov-selective hydroaminocarbonylation of alkynes to afford α,β-unsaturated amides, but also facilitates a sequential four-component hydroaminocarbonylation/radical alkylation in the presence of tertiary and secondary alkyl boronate esters, which allows for straightforward conversion of alkynes into corresponding amides. Preliminary mechanistic studies disclose that a photoinduced oxidative insertion of aniline and CO into nickel followed by a migratory insertion of (carbamoyl)nickel species could be involved.

Dual Nickel/Photoredox-Catalyzed Deaminative Cross-Coupling of Sterically Hindered Primary Amines

We report a method to activate α-3° amines for deaminative arylation via condensation with an electron-rich aldehyde and merge this reactivity with nickel metallaphotoredox to generate benzylic quaternary centers, a common motif in pharmaceuticals and natural products. The reaction is accelerated by added ammonium salts. Evidence is provided in support of two roles for the additive: inhibition of nickel black formation and acceleration of the overall reaction rate. We demonstrate a robust scope of amine and haloarene coupling partners and show an expedited synthesis of ALK2 inhibitors.