Arylzinc Reagents Research Articles

Nickel-catalyzed carboxylation of aryl zinc reagent with CO2: A theoretical and experimental study

Two Ni-complexes with 1,1′-bis(diphenylphosphino)ferrocene (dppf) and tricyclohexylphosphine (PCy3) ligands were tested for the Ni-catalyzed cross-coupling of aryl zinc reagent with CO2 to form aryl carboxylic acid. Theoretical study with the aid of density functional theory (DFT) was carried out to understand the detailed reaction mechanism. The reasonable reaction pathway was deduced. The simulation results suggested that the free energy barrier of the rate-limiting step with (dppf)Ni is only 1.64 kcal mol−1 higher than the barrier with (PCy3)2Ni. However, our experiment provided an unexpectedly low yield by using (dppf)Ni complex as the catalyst. Further theoretical study ascribed the shortage of the reaction yield to the weak CO2 capture ability of the (dppf)Ni complex. Two additional ligands 1,2-bis(diphenylphosphino)ethane (dppe) and 1,4-bis(diphenylphosphino)butane (dppb) were also taken into account to verify the ligand effect in our reactions.

Reaction of Quinoline N‐Oxides and Pyridine N‐Oxides with Arylzinc Reagents: Synthesis of 2‐Arylquinolines and 2‐Arylpyridines

AbstractReaction of quinoline N‐oxides and pyridine N‐oxides with arylzinc reagents under transition‐metal‐free conditions was studied. The reaction was carried out in toluene (for quinoline N‐oxides) or THF (for pyridine N‐oxides) at 100 °C and required 2 equiv. of arylzinc loadings and the presence of 2.5 equiv. of TFAA, affording 2‐arylquinolines and 2‐arylpyridines, respectively, in 24% to 95% yields. Functional groups OMe, F, Cl, Br, CF3, C(O)NH2, COOR and NO2 were tolerated. Mechanistic studies showed that the reaction of quinoline N‐oxides proceeded via a 2‐arylquinolin‐1(2H)‐olate intermediate, and the reaction of pyridine N‐oxides via a 5‐arylpenta‐2,4‐dienal oxime intermediate.

Synergistic Bimetallic Ni/Ag and Ni/Cu Catalysis for Regioselective γ,δ-Diarylation of Alkenyl Ketimines: Addressing β-H Elimination by in Situ Generation of Cationic Ni(II) Catalysts

We disclose unprecedented synergistic bimetallic Ni/Ag and Ni/Cu catalysts for regioselective γ,δ-diarylation of unactivated alkenes in simple ketimines with aryl halides and arylzinc reagents. The bimetallic synergy, which generates cationic Ni(II) species during reaction, promotes migratory insertion and transmetalation steps and suppresses β-H elimination and cross-coupling, the major side reactions that cause serious problems during alkene difunctionalization. This diarylation reaction proceeds at remote locations to imines to afford, after simple H+ workup, diversely substituted γ,δ-diaryl ketones that are otherwise difficult to access readily with existing methods.

Rhodium-Catalyzed Arylzincation of Alkynes: Ligand Control of 1,4-Migration Selectivity.

The addition of arylzinc reagents ArZnCl 1 to alkynes 2 was found to be catalyzed by rhodium complexes in the presence of a catalytic amount of zinc chloride. The selectivity in giving 2-arylalkenylzinc species 3 or ortho-alkenylarylzinc species 4, the latter of which is generated through 1,4-Rh migration from alkenyl to aryl in the catalytic cycle, is controlled by the ligands on rhodium. Ligands cod and binap gave 3 and 4, respectively, with high selectivity.

Transition-Metal-Free Arylation and Alkylation of Diarylmethyl p-Tolyl Sulfones with Zinc Reagents.

The transition-metal-free synthesis of unsymmetrical and highly functionalized triarylmethanes through arylation of the situ generated o-QMs from diarylmethyl p-tolyl sulfones with aryl zinc reagents is described. Alkyl zinc reagents are also well tolerated in this reaction. Additionally, the straightforward synthesis of the analogue of the antituberculosis agent A and the key precursor of the anti-breast-cancer agent B are achieved by this strategy.

Ni-Catalyzed Regioselective Alkylarylation of Vinylarenes via C(sp3)-C(sp3)/C(sp3)-C(sp2) Bond Formation and Mechanistic Studies.

We report a Ni-catalyzed regioselective alkylarylation of vinylarenes with alkyl halides and arylzinc reagents to generate 1,1-diarylalkanes. The reaction proceeds well with primary, secondary and tertiary alkyl halides, and electronically diverse arylzinc reagents. Mechanistic investigations by radical probes, competition studies and quantitative kinetics reveal that the current reaction proceeds via a Ni(0)/Ni(I)/Ni(II) catalytic cycle by a rate-limiting direct halogen atom abstraction via single electron transfer to alkyl halides by a Ni(0)-catalyst.

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

We disclose a [(PhO)3P]/NiBr2-catalyzed regioselective β,δ-diarylation of unactivated olefins in ketimines with aryl halides and arylzinc reagents. This diarylation proceeds at remote locations to the carbonyl group to afford, after simple H+ workup, diversely substituted β,δ-diarylketones that are otherwise difficult to access readily with existing methods. Deuterium-labeling and crossover experiments indicate that diarylation proceeds by ligand-enabled contraction of transient nickellacycles.

Direct Arylation of Benzyl Ethers with Organozinc Reagents.

A novel C(sp3)-H bond arylation of benzyl ethers with Knochel-type arylzinc reagents has been developed. This transition-metal-catalyst-free reaction proceeds well under mild conditions in a simple and effective manner and enables the synthesis of a wide range of potentially biologically active benzyl ethers by using highly functionalized organozinc reagents as a carbon nucleophile.

Synthesis of some ketones via nano-nickel oxide catalyzed acylation of arylzinc reagents; strategy involving the use of mixed (methyl)(aryl)zincs

Nano-NiO catalyzed acylation of mixed (methyl)(aryl)zincs with aromatic acyl halides in THF at room temperature provides a new facile route for aryl-aroyl coupling. Among NiCl$_{2}$.L$_{2}$ and NiCl$_{2}$.L (L = monodentate and bidentate phosphine ligand) catalysts, the lower catalyst loading of NiCl$_{2}$ (dppf) may seem attractive; however, nano-NiO, being the lowest cost catalyst, is more favorable for aroylation of (methyl)(aryl)zincs. This procedure also provides a supplement to Cu and Pd catalyzed acylation of diorganozincs.

Ni-Catalyzed Regioselective Dicarbofunctionalization of Unactivated Olefins by Tandem Cyclization/Cross-Coupling and Application to the Concise Synthesis of Lignan Natural Products.

We disclose a (terpy)NiBr2-catalyzed reaction protocol that regioselectively difunctionalizes unactivated olefins with tethered alkyl halides and arylzinc reagents. The reaction shows an excellent functional group tolerance (such as ketones, esters, nitriles, and halides) and a moderate to good level of diastereoselectivity. The current cyclization/cross-coupling also tolerates molecules containing base-sensitive racemizable stereocenters, which are preserved without racemization during the reaction. This cyclization/cross-coupling provides a rapid access to (arylmethyl)carbo- and heterocyclic scaffolds, which occur widely as structural cores in various natural products and bioactive molecules. In order to show synthetic utility and generality, we have applied this new method in gram-scale quantities to the concise synthesis of six lignan natural products containing three different structural frameworks. We further conducted mechanistic investigations with radical probes and selectivity studies, which indicated that the current reaction proceeds via a single electron transfer (SET) process.

Modular radical cross-coupling with sulfones enables access to sp3-rich (fluoro)alkylated scaffolds.

Cross-coupling chemistry is widely applied to carbon-carbon bond formation in the synthesis of medicines, agrochemicals, and other functional materials. Recently, single-electron-induced variants of this reaction class have proven particularly useful in the formation of C(sp2)-C(sp3) linkages, although certain compound classes have remained a challenge. Here, we report the use of sulfones to activate the alkyl coupling partner in nickel-catalyzed radical cross-coupling with aryl zinc reagents. This method's tolerance of fluoroalkyl substituents proved particularly advantageous for the streamlined preparation of pharmaceutically oriented fluorinated scaffolds that previously required multiple steps, toxic reagents, and nonmodular retrosynthetic blueprints. Five specific sulfone reagents facilitate the rapid assembly of a vast set of compounds, many of which contain challenging fluorination patterns.

Ni-catalysed regioselective 1,2-diarylation of unactivated olefins by stabilizing Heck intermediates as pyridylsilyl-coordinated transient metallacycles.

We report a Ni-catalysed diarylation of unactivated olefins in dimethylpyridylvinylsilane by intercepting Heck C(sp3)-NiX intermediates, derived from aryl halides, with arylzinc reagents. This approach utilizes a modifiable pyridylsilyl moiety as a coordinating group that plays a dual role of intercepting oxidative addition species to promote Heck carbometallation, and stabilizing the Heck C(sp3)-NiX intermediates as transient metallacycles to suppress β-hydride elimination, and facilitate transmetalation/reductive elimination. This method affords 1,2-diarylethylsilanes, which can be readily oxidized to 1,2-diarylethanols that occur as structural motifs in 3-aryl-3,4-dihydroisocoumarin and dihydrostilbenoid natural products.

Nickel-catalyzed cross-coupling of β-carbonyl alkenyl pivalates with arylzinc chlorides.

The nickel-catalyzed cross-coupling reaction of β-carbonyl alkenyl pivalates with arylzinc reagents generates 3-aryl-substituted α,β-unsaturated carbonyl compounds via C-O bond cleavage. The reaction features mild reaction conditions, a wide scope of substrates, and good functional group tolerance.

Insights into the Cobalt-Catalyzed Three-Component Coupling of Mixed Aromatic Organozinc Species, Carbonyl Compounds or Imines and Michael Acceptors: Synthetic and Mechanistic Aspects

The first examples of cobalt-catalyzed multicomponent couplings of mixed aromatic arylzinc reagents with Michael acceptors and carbonyl compounds or imines is described. The reaction system employs a cobalt(II)-2,2′-bipyridine or a cobalt(II)-1,10-phenanthroline complex as a catalyst for both organozinc generation and subsequent multicomponent assembly by formal Michael addition/aldol coupling or Mannich reaction. This study brings new insights into the synthetic scope and mechanism of the reaction.

Transition-Metal-Free Cross-Coupling of Aryl and Heteroaryl Thiols with Arylzinc Reagents.

Cross-coupling of (hetero)arylthiols with arylzinc reagents via C-S cleavage was performed under transition-metal-free conditions. The reaction displays a wide scope of substrates and high functional-group tolerance. Electron-rich and -deficient (hetero)arylthiols and arylzinc reagents can be employed in this transformation. Mg2+ and Li+ ions were demonstrated to facilitate the reaction.

Nickel-Catalyzed Cross-Coupling Reaction of Aryl Sulfoxides with Arylzinc Reagents: When the Leaving Group is an Oxidant

Nickel-catalyzed Negishi-type cross-coupling of aryl methyl sulfoxides with arylzinc reagents has been developed. By consuming the catalyst-oxidizing methanesulfenate anion through oxidative homocoupling of the arylzinc reagent, smooth catalyst turnover could be executed. Arylzinc reagents prepared from arylmagnesium bromide, zinc bromide, and lithium bromide were optimal to afford the products in good to high yields, while arylzinc reagents prepared through other procedures showed lower reactivities. The reactivity of aryl methyl sulfoxide was compared with that of typical aryl (pseudo)halides.

Ni-Catalyzed Regioselective 1,2-Dicarbofunctionalization of Olefins by Intercepting Heck Intermediates as Imine-Stabilized Transient Metallacycles.

We disclose a strategy for Ni-catalyzed dicarbofunctionalization of olefins in styrenes by intercepting Heck C(sp3)-NiX intermediates with arylzinc reagents. This approach utilizes a readily removable imine as a coordinating group that plays a dual role of intercepting oxidative addition species derived from aryl halides and triflates to promote Heck carbometalation and stabilizing the Heck C(sp3)-NiX intermediates as transient metallacycles to suppress β-hydride elimination and facilitate transmetalation/reductive elimination steps. This method affords diversely substituted 1,1,2-triarylethyl products that occur as structural motifs in various natural products.

Nickel-Catalyzed Negishi Cross-Coupling of N-Acylsuccinimides: Stable, Amide-Based, Twist-Controlled Acyl-Transfer Reagents via N–C Activation

This paper reports a room temperature, nickel-catalyzed Negishi cross-coupling of N-acylsuccinimides with arylzinc reagents via selective N–C bond cleavage enabled by amide bond twist. The reaction proceeds using a commercially available, air-stable Ni(II) precatalyst in the absence of additives under exceedingly mild conditions. Of broad interest, this report introduces N-acylsuccinimides as stable, crystalline, electrophilic, cost-effective, benign, amide-based acyl transfer reagents via acyl metal intermediates. The reaction selectivity is governed by half-twist of the amide bond in N-acylsuccinimides, thus opening the door for applications in metal-catalyzed manifolds via redox­-neutral reaction pathways tuneable by amide bond distortion.

Efficient C(sp3)–H Bond Arylation of Tetrahydroisoquinolines with Knochel-Type Arylzinc Reagents under Oxidative Conditions

A novel C(sp3)–H bond arylation of tetrahydroisoquinoline (THIQ) derivatives with Knochel-type arylzinc reagents has been developed. In the presence of MgCl2, arylzinc reagents readily reacted with THIQ derivatives under oxidative conditions, affording a wide range of potentially biologically active compounds in good yields. Moreover, the developed method can tolerate a variety of sensitive functional groups such as an ester group.

Synthesis of Donor–Acceptor-Type Benzo[b]phosphole and Naphtho[2,3-b]phosphole Oxides and Their Solvatochromic Properties

A series of donor–acceptor-type benzo[b]phosphole and naphtho[2,3-b]phosphole oxides have been synthesized through metal-catalyzed reactions as key steps: that is, (1) cobalt- and copper-catalyzed multicomponent coupling of an arylzinc reagent, an alkyne, and dichlorophenylphosphine to assemble the electron-deficient benzophosphole or naphthophosphole oxide core and (2) palladium-catalyzed cross-coupling to introduce an electron-donating substituent to the “benzo” or “naphtho” moiety. These donor–acceptor molecules are strongly fluorescent, showing weak to strong solvatochromism depending on the electron-donating substituent.