Ni-Catalyzed Regioselective β,δ-Diarylation of Unactivated Olefins in Ketimines via Ligand-Enabled Contraction of Transient Nickellacycles: Rapid Access to Remotely Diarylated Ketones

Palladium-Catalyzed γ,γ'-Diarylation of Free Alkenyl Amines

The direct difunctionalization of alkenes is an effective way to construct multiple C-C bonds in one-pot using a single functional group. The regioselective dicarbofunctionalization of alkenes is therefore an important area of research to rapidly obtain complex organic molecules. Herein, we report a palladium-catalyzed γ,γ'-diarylation of free alkenyl amines through interrupted chain walking for the synthesis of Z-selective alkenyl amines. Notably, while 1,3-dicarbofunctionalization of allyl groups is well precedented, the present disclosure allows 1,3-dicarbofunctionalization of highly substituted allylamines to give highly Z-selective trisubsubstituted olefin products. This cascade reaction operates via an unprotected amine-directed Mizoroki-Heck (MH) pathway featuring a β-hydride elimination to selectively chain walk to furnish a new terminal olefin which then generates the cis-selective alkenyl amines around the sterically crowded allyl moiety. This operationally simple protocol is applicable to a variety of cyclic, branched, and linear secondary and tertiary alkenylamines, and has a broad substrate scope with regard to the arene coupling partner as well. Mechanistic studies have been performed to help elucidate the mechanism, including the presence of a likely unproductive side C-H activation pathway.

1,3-Difunctionalization of alkenes: state-of-the-art and future challenges

This review summarizes the advances in 1,3-difunctionalization of alkenes mediated by Pd-, Ni-, Fe-, and Cu-based catalysts, as well as under metal-free conditions, with an emphasis on the reaction mechanisms and factors governing regioselectivity.

Mechanisms and origins of regioselectivities of nickel-catalyzed β,δ-vinylarylation of alkenyl esters with vinyl triflates and arylzinc reagents

DFT calculations were performed to explore the mechanisms, origins of regioselectivity and substituent-controlled reactivity in the β,δ-vinylarylation of alkenyl esters catalyzed by nickel catalysts.

Ni-Catalyzed Regioselective 1,2-Dialkylation of Alkenes Enabled by the Formation of Two C(sp3)-C(sp3) Bonds

We disclose a Ni-catalyzed vicinal difunctionalization of alkenes with benzyl halides and alkylzinc reagents, which produces products with two new alkyl-alkyl bonds. This alkene dialkylation is effective in combining secondary benzyl halides and secondary alkylzinc reagents with internal alkenes, which furnishes products with three contiguous all-carbon secondary stereocenters. The products can be readily elaborated to access complex tetralene, benzosuberene, and bicyclodecene cores. The reaction also features as the most efficient alkene difunctionalization process to date with catalyst loadings down to 500 ppm and the catalytic turnover number (TON) and turnover frequency (TOF) registering up to 2 × 103 and 165 h-1 at rt, respectively.

General Method for Enantioselective Three-Component Carboarylation of Alkenes Enabled by Visible-Light Dual Photoredox/Nickel Catalysis

A visible-light-promoted photoredox/nickel protocol for the enantioselective three-component carboarylation of alkenes with tertiary and secondary alkyltrifluoroborates and aryl bromides is described. This redox-neutral protocol allows for facile and divergent access to a wide array of enantioenriched β-alkyl-α-arylated carbonyls, phosphonates, and sulfones in high yields and excellent enantioselectivities from readily available starting materials. We also report a modular and enantioselective synthesis of flurbiprofen analogs and piragliatin lead compound to demonstrate synthetic utility. Experimental and computational mechanistic studies were performed to gain insights into the mechanism and origin of chemo- and enantioselectivity.

NiH-Catalyzed Proximal-Selective Hydroamination of Unactivated Alkenes

Reported herein is a modular, NiH-catalyzed system capable of proximal-selective hydroamination of unactivated alkenes with diverse amine sources. The key to the successful implementation of this approach is the promotion of NiH insertion into even highly substituted olefins via coordination of the bidentate directing group to the nickel complex. A wide range of primary and secondary amines can be installed in both internal and terminal unactivated alkenes with excellent regiocontrol under the optimized reaction conditions. This protocol is flexible and general for the preparation of a variety of valuable β- and γ-amino acid building blocks that would otherwise be difficult to synthesize. The utility of this transformation was further demonstrated by the site-selective late-stage modification of complex and medicinally relevant molecules. Combined experimental and computational studies illuminate the detailed reaction mechanism.

Alkyl halides as both hydride and alkyl sources in catalytic regioselective reductive olefin hydroalkylation

Among the plethora of catalytic methods developed for hydrocarbofunctionalization of olefins to date, reactions that regioselectively install a functionalized alkyl unit at the 2-position of a terminal unactivated C=C bond to afford branched products are scarce. Here, we show that a Ni-based catalyst in conjunction with a stoichiometric reducing agent promote Markovnikov-selective hydroalkylation of unactivated alkenes tethered to a recyclable 8-aminoquinaldine directing auxiliary. These mild reductive processes employ readily available primary and secondary haloalkanes as both the hydride and alkyl donor. Reactions of alkenyl amides with ≥ five-carbon chain length regioselectively afforded β-alkylated products through remote hydroalkylation, underscoring the fidelity of the catalytic process and the directing group’s capability in stabilizing five-membered nickelacycle intermediates. The operationally simple protocol exhibits exceptional functional group tolerance and is amenable to the synthesis of bioactive molecules as well as regioconvergent transformations.

Methods that regioselectively install a functionalized alkyl unit at the 2-position of a terminal unactivated C=C bond are scarce. Here, the authors report a Markovnikov-selective hydroalkylation of unactivated amide-tethered alkenes catalyzed by nickel in conjunction with a stoichiometric reductant.

Walking metals: catalytic difunctionalization of alkenes at nonclassical sites

Migration of metals along a carbon chain is triggered by two of the most common organometallic elementary steps - β-hydride (β-H) elimination and alkene hydrometallation. This process heralds a new future for creating bonds at carbon sites that fall outside the tenets of the conventional wisdom for reactivity and bond formation, and provides an opportunity to leverage β-H elimination to advance the very reaction of alkene difunctionalization it is intrinsically predestined to disrupt. Almost four decades since its genesis, the early adventure for alkene difunctionalization by metal migration was sporadic, and its later development went on a hiatus primarily due to original impetus on arresting β-H elimination for vicinal alkene difunctionalization. With the recent surge on alkene difunctionalization, efforts have been gradually shifting to harnessing the process of β-H elimination to difunctionalize alkenes at sites other than the classical vicinal carbons, termed henceforth nonclassical reaction sites for pedagogical simplicity. In this review article, we extricate and examine the origin and the development of such reactions over the years. This review covers a wide range of reactions for the difunctionalization of alkenes at geminal (1,1), allylic (1,3) and remote (1,n) carbon sites with a variety of coupling partners. These reactions have enabled engineering of complex molecular frameworks with the generation of new carbon-carbon (C-C)/C-C, C-C/C-heteroatom (halogens, O, N, B) and C-B/C-B bonds. The development of these unique transformations is also presented with mechanistic hypotheses and experimental evidences put forward by researchers. Judged by the number of reports emerging recently, it is now strikingly evident that the field of alkene difunctionalization by metal migration has begun to gain momentum, which holds a great future prospect to develop into a synthetic method of enormous potential.

Nickel-Catalyzed Reductive Aryl Thiocarbonylation of Alkene via Thioester Group Transfer Strategy

Herein reported is a nickel-catalyzed reductive aryl thiocarbonylation of alkene via thioester group transfer strategy by using simple and readily available thioesters. In contrast to traditional activation of weaker C(acyl)-S bond, the C(acyl)-C bond of thioester was selectively cleaved to enable this reaction under mild conditions. Furthermore, this approach features operational simplicity and broad substrate scope, providing a complementary and practical route for thioester synthesis without requiring toxic thiol or CO gas.

Nickel-catalyzed three-component olefin reductive dicarbofunctionalization to access alkylborates

We report a three-component olefin reductive dicarbofunctionalization for constructing alkylborates, specifically, nickel-catalyzed reductive dialkylation and alkylarylation of vinyl boronates with a variety of alkyl bromides and aryl iodides. This reaction exhibits good coupling efficiency and excellent functional group compatibility, providing convenient access to the late-stage modification of complex natural products and drug molecules. Combined with alkylborate transformations, this reaction could also find applications in the modular and convergent synthesis of complex compounds.

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.

Ligand-Enabled Nickel-Catalyzed Redox-Relay Migratory Hydroarylation of Alkenes with Arylborons

A redox-relay migratory hydroarylation of isomeric mixtures of olefins with arylboronic acids catalyzed by nickel complexes bearing diamine ligands is described. A range of structurally diverse 1,1-diarylalkanes, including those containing a 1,1-diarylated quaternary carbon, were obtained in excellent yields and with high regioselectivity. Preliminary experimental evidence supports the proposed non-dissociated chainwalking of aryl-nickel(II)-hydride species along the alkyl chain of alkenes before selective reductive elimination at a benzylic position. A catalyst loading as low as 0.5 mol % proved to be sufficient in large-scale synthesis while retaining high reactivity, highlighting the practical value of this transformation.

Recent developments in nickel-catalyzed intermolecular dicarbofunctionalization of alkenes

Nickel-catalyzed three-component alkene difunctionalization has rapidly emerged as a powerful tool for forging two C-C bonds in a single reaction. Building upon the powerful modes of bond construction in traditional two-component cross-coupling, various research groups have demonstrated the versatility of nickel in enabling catalytic 1,2-dicarbofunctionalization using a wide range of carbon-based electrophiles and nucleophiles and in a fully intermolecular fashion. Though this area has emerged only recently, the last few years have witnessed a proliferation of publications on this topic, underscoring the potential of this strategy to develop into a general platform that offers high regio- and stereoselectivity. This minireview highlights the recent progress in the area of intermolecular 1,2-dicarbofunctionalization of alkenes via nickel catalysis and discusses lingering challenges within this reactivity paradigm.

An Expedient Route to 9-arylmethylanthracene Derivatives via Tandem Ni-catalyzed Alkene Dicarbofunctionalization and Acid-promoted Cyclization-aromatization

We report a nickel-catalyzed one pot synthesis of 9-arylmethylanthracene motifs, which find applications in medicinal and material chemistry. In this synthesis, we apply three component alkene dicarbofunctionalization of 2-vinylaldimines with aryl iodides and arylzinc reagent to generate a 1,1,2-diarylethyl scaffold, which then undergoes an acidpromoted cyclization followed by aromatization to furnish 9-arylmethylanthracene cores. With the new method, a number of differently-substituted 9-arylmethylanthracene derivatives can be synthesized in good yields.

Pd-Catalyzed Alkene Difunctionalization Reactions of Enolates for the Synthesis of Substituted Bicyclic Cyclopentanes

Palladium-catalyzed alkene difunctionalization reactions between alkenes bearing tethered aryl or alkenyl triflates and enolate nucleophiles are described. The transformations form two C-C bonds, a ring, and up to two stereocenters, while producing substituted cyclopentane derivatives that contain appended carbonyl functionality. Products are formed with up to >20:1 diastereoselectivity, and formation of sterically congested bonds between quaternary carbon atoms is feasible.

Three-component vicinal-diarylation of alkenes via direct transmetalation of arylboronic acids

Transmetalation-initiated three-component vicinal-diarylation of alkenes.

Herein, we report three-component vicinal-diarylation of non-conjugated alkenes initiated by transmetalation of arylboronic acids, which provides complementary access to β,γ-diaryl carbonyl compounds. We have also screened a large number of chiral ligands for developing an enantioselective version of this reaction and obtained the preliminary results (up to 79 : 21 e.r.). Notably, the methodology developed herein represents the first three component syn-vicinal-dicarbofunctionalization of non-conjugated alkenes involving palladium catalysis.

Construction of Acyclic Quaternary Carbon Stereocenters by Catalytic Asymmetric Hydroalkynylation of Unactivated Alkenes

Quaternary carbon stereocenters are common structural motifs in organic synthesis. The construction of these stereocenters in a catalytic and enantioselective manner remains a prominent synthetic challenge. In particular, methods for the synthesis of alkyne-substituted quaternary carbon stereocenters are very rare. Previous catalytic systems for hydroalkynylation of alkenes create tertiary stereocenters. We describe here an iridium catalyzed asymmetric hydroalkynylation of nonactivated trisubstituted alkene. The hydroalkynylation of β,γ-unsaturated amides occurs with high regio- and enantioselectivities to afford alkyne-substituted acyclic quaternary carbon stereocenters. Computational and experimental data suggest that the enantioselectivity is not only determined by the facial selectivity of the alkene but also by an alkene isomerization process. This strategy provides an efficient method to access alkyne-substituted acyclic quaternary carbon stereocenters with minimally functionalized starting materials.