Palladium(ii)-catalyzed γ-selective hydroarylation of alkenyl carbonyl compounds with arylboronic acids

Visible-Light-Induced Difunctionalization of 3-Butenoic Acid with Bromodifluoromethyl Heteroarylsulfones

Herein, we report a visible-light-induced iridium-promoted direct bifunctionalization of 3-butenoic acid with bromodifluoromethyl heteroarylsulfones. This methodology enables the concurrent introduction of difluoromethyl heteroarylsulfone and bromine groups into 3-butenoic acid under mild reaction conditions. Various α-substituted 3-butenoic acids and bromodifluoromethyl heteroarylsulfones were found to be compatible, yielding the corresponding products in moderate to good yields. This method opens a new route for the synthesis of fluorocarboxylic acid derivatives.

Palladium-Catalyzed Reductive Heck Hydroarylation of Unactivated Alkenes Using Hydrosilane at Room Temperature

The reductive Heck hydroarylation of unactivated alkenes has emerged as an essential reaction for regioselective hydroarylation. Herein, we report a palladium-catalyzed reductive Heck hydroarylation of unactivated alkenes under mild conditions with enhanced functional group tolerance using hydrosilane as the reducing reagent. Under the optimal conditions, the alkylarene yields increased, resulting in minimal undesired products. Mechanistic studies using deuterated reagents indicated the involvement of two competing catalytic cycles.

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.

Palladium-Catalyzed E-Selective Oxidative Amination of Aromatic Amine with 3-Butenoic Acid

A palladium-catalyzed oxidative amination of inactive olefins with an aromatic amine was developed using a copper acetate oxidant to yield corresponding secondary and tertiary enamines in moderate to good yields. This new procedure outlines an efficient approach for the construction of enamine skeletons.

Regio- and chemoselective hydroamination of unactivated alkenes with anthranils via NiH-catalysis

A NiH-catalyzed polarity-reversed hydroamination of β,γ-, γ,δ- and δ,ε-unsaturated alkenes with electrophilic anthranils was developed. This reaction proceeds in a highly regio- and chemoselective manner to afford γ, δ and ε-arylamines bearing a carbonyl or alcohol functionality with 100% atom efficiency. Preliminary mechanistic studies indicate that the chemoselectivity is controlled by the base and the alcohol product is derived from the base-catalyzed hydrosilylation of the CO bond.

A Sterically Tuned Directing Auxiliary Promotes Catalytic 1,2-Carbofluorination of Alkenyl Carbonyl Compounds

The site-selective palladium-catalyzed three-component coupling of unactivated alkenyl carbonyl compounds, aryl- or alkenylboronic acids, and N-fluorobenzenesulfonimide is described herein. Tuning of the steric environment on the bidentate directing auxiliary enhances regioselectivity and facilitates challenging C(sp³ )-F reductive elimination from a Pd^IV intermediate to afford 1,2-carbofluorination products in moderate to good yields.

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.

Regio- and Stereoselective 1,2-Oxyhalogenation of Non-Conjugated Alkynes via Directed Nucleopalladation: Catalytic Access to Tetrasubstituted Alkenes

A catalytic 1,2-oxyhalogenation method that converts non-conjugated internal alkynes into tetrasubstituted alkenes with high regio- and stereoselectivity is described. Mechanistically, the reaction involves a Pd^II /Pd^IV catalytic cycle that begins with a directed oxypalladation step. The origin of regioselectivity is the preference for formation of a six-membered palladacycle intermediate, which is facilitated by an N,N-bidentate 2-(pyridin-2-yl)isopropyl (PIP) amide directing group. Selectivity for C(alkenyl)-X versus -N (X=halide) reductive elimination from the Pd^IV center depends on the identity of the halide anion; bromide and iodide engage in C(alkenyl)-X formation, while intramolecular C(alkenyl)-N reductive elimination occurs with chloride to furnish a lactam product. DFT calculations shed light on the origins of this phenomenon.

Access to dialkylated allylic stereogenic centers by Ni-catalysed enantioselective hydrovinylation of unactivated alkenes

Tertiary dialkylated allylic stereogenic centers are widespread substructures in bioactive molecules and natural products. However, enantioselective access to dialkyl substituted allylic motifs remains a long-term challenge. Herein, a straightforward protocol to build allylic dialkylated stereogenic centers enabled by nickel-catalysed regio- and enantioselective hydrovinylation of isolated unactivated alkenes facilitated by a weakly coordinating group with vinyl bromides was developed, affording dialkylated allylic species in good yields with excellent enantioselectivities. The reaction distinguishes distinct alkenes and works for both terminal and internal aliphatic alkenes. The reaction proceeds under mild conditions and tolerates a wide range of functional groups.

Carboxylic Acid-Directed Manganese(I)-Catalyzed Regioselective Hydroarylation of Unactivated Alkenes

A carboxylic acid-directed regioselective hydroarylation reaction of unactivated alkenes with aryl boronic acids was reported. This transformation was enabled by homogeneous manganese catalyst MnBr(CO)₅ in the presence of KOH and H₂O in the m-xylene reaction medium. Both internal and terminal alkenes worked well in this transformation, and a series of functional groups were tolerated. This reaction not only provided an expeditious method to prepare γ-aryl carboxylic acids from simple starting materials but also would inspire further studies in employing homogeneous manganese catalysis in organic synthesis.

Nickel-Catalyzed Chemo- and Regioselective Arylcyanation of β,γ-Unsaturated Amides

A nickel-catalyzed intermolecular arylcyanation of 8-aminoquinolinyl β,γ-unsaturated amides is reported. The three-component reaction directly afforded diverse β-cyano γ-aryl amides with exclusive chemo- and regioselectivity. The synthetic practicality of this approach is further demonstrated through multigram scale reaction, expanded transformations of the nitrile product, late-stage modification of complex molecules, and direct drug synthesis.

Mapping Ambiphile Reactivity Trends in the Anti-(Hetero)annulation of Non-Conjugated Alkenes via PdII /PdIV Catalysis

In this study, we systematically evaluate different ambiphilic organohalides for their ability to participate in anti-selective carbo- or heteroannulation with non-conjugated alkenyl amides under Pd^II /Pd^IV catalysis. Detailed optimization of the reaction conditions has led to protocols for synthesizing tetrahydropyridines, tetralins, pyrrolidines, and other carbo/heterocyclic cores via [n+2] (n=3-5) (hetero)annulation. Expansion of scope to otherwise unreactive ambiphilic haloketones through Pd^II /amine co-catalysis is also demonstrated. Compared to other annulation processes, this method proceeds via a distinct Pd^II /Pd^IV mechanism involving Wacker-type directed nucleopalladation. This difference results in unique reactivity and selectivity patterns, as revealed through assessment of reaction scope and competition experiments.

DFT Case Study on the Comparison of Ruthenium-Catalyzed C-H Allylation, C-H Alkenylation, and Hydroarylation

Density functional calculations at the B3LYP-D3+IDSCRF/TZP-DKH(-dfg) level of theory have been performed to understand the mechanism of ruthenium-catalyzed C-H allylation reported in the literature in depth. The plausible pathway consisted of four sequential processes, including C-H activation, migratory insertion, amide extrusion, and recovery of the catalyst, in which C-H activation was identified as the rate-determining step. The amide extrusion step could be promoted kinetically by trifluoroacetic acid since its mediation lowered the free-energy barrier from 32.1 to 12.2 kcal/mol. Additional calculations have been performed to explore other common pathways between arenes and alkenes, such as C-H alkenylation and hydroarylation. A comparison of the amide extrusion and β-H elimination steps established the following reactivity sequence of the leaving groups: protonated amide group > β-H group > unprotonated amide group. The suppression of hydroarylation was attributed to the sluggishness of the Ru-C protonation step as compared to the amide extrusion step. This study can unveil factors favoring the C-H allylation reaction.

Controllable access to trifluoromethyl-containing indoles and indolines: Palladium-catalyzed regioselective functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides

The synthesis of diverse products from the same starting materials is always attractive in organic chemistry. Here, a palladium-catalyzed substrate-controlled regioselective functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides has been developed, which provides a direct but controllable access to a variety of structurally diverse trifluoromethyl-containing indoles and indolines. In more detail, with respect to γ,δ-alkenes, 1,1-geminal difunctionalization of unactivated alkenes with trifluoroacetimidoyl chloride enables the [4 + 1] annulation to produce indoles; as for β,γ-alkenes, a [3 + 2] heteroannulation with the hydrolysis product of trifluoroacetimidoyl chloride through 1,2-vicinal difunctionalization of alkenes occurs to deliver indoline products. The structure of alkene substrates differentiates the regioselectivity of the reaction.

A palladium-catalyzed dual functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides toward the synthesis of structurally diverse trifluoromethyl-containing indoles and indolines has been developed.

Nickel(0)-catalysed linear-selective hydroarylation of 2-aminostyrenes with arylboronic acids by a bifunctional temporary directing group strategy

We report a nickel(0)-catalyzed linear-selective hydroarylation of 2-aminostyrenes with arylboronic acids using a bifunctional temporary directing group strategy. In the presence of a catalytic amount of commercially available 3,5-dibromosalicylaldehyde, an...

Regioselective Hydroalkylation of Vinylarenes by Cooperative Cu and Ni Catalysis

Disclosed here is a dual copper and nickel catalytic system with a silyl hydride source for promoting the linear selective hydroalkylation of vinylarenes. This carbon-carbon bond-forming protocol is applied to couple a variety of functionalized vinylarenes with alkyl halides applying a nickel(II) NNN pincer complex in the presence of an NHC-ligated copper catalyst. This combination allows for a 1 mol % loading of the nickel catalyst leading to turnover numbers of up to 72. Over 40 examples are presented, including applications for pharmaceutical diversification. Labeling experiments demonstrated the regioselectivity of the reaction and revealed that the copper catalyst plays a crucial role in enhancing the rate for formation of the reactive linear alkyl nickel complex. Overall, the presented work provides a complimentary approach for hydroalkylation reactions, whilst providing a preliminary mechanistic understanding of the cooperativity between the copper and nickel complexes.

Directed Markovnikov hydroarylation and hydroalkenylation of alkenes under nickel catalysis

We report a full account of our research on nickel-catalyzed Markovnikov-selective hydroarylation and hydroalkenylation of non-conjugated alkenes, which has yielded a toolkit of methods that proceed under mild conditions with alkenyl sulfonamide, ketone, and amide substrates. Regioselectivity is controlled through catalyst coordination to the native Lewis basic functional groups contained within these substrates. To maximize product yield, reaction conditions were fine-tuned for each substrate class, reflecting the different coordination properties of the directing functionality. Detailed kinetic and computational studies shed light on the mechanism of this family of transformations, pointing to transmetalation as the turnover-limiting step.

Native Lewis basic functional groups enable the nickel-catalyzed Markovnikov-selective hydroarylation and hydroalkenylation of unactivated alkenes with organoboron reagents.

Modular synthesis of non-conjugated N-(quinolin-8-yl) alkenyl amides via cross-metathesis

We report a direct and modular method to access non-conjugated alkenyl amides containing the 8-aminoquinoline (AQ) directing auxiliary and related groups via cross-metathesis. In this way, readily available, AQ-containing, terminal β,γ-unsaturated amides can be coupled with various terminal alkenes to furnish internal alkene products that are otherwise difficult to prepare. The value of this family of products stems from their ability to participate in a number of directed alkene functionalization reactions.

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

Alkene hydrocarbofunctionalization represents one of the most important classes of chemical transformations, but related branched-selective examples with unactivated olefins are scarce. Here, we report that catalytic amounts of a dimeric Ni(I) complex and an exogenous alkoxide base promote Markovnikov-selective hydroarylation(alkenylation) of unactivated and activated olefins using organo bromides or triflates derived from widely available phenols and ketones. Products bearing aryl- and alkenyl-substituted tertiary and quaternary centers could be isolated in up to 95% yield and >99:1 regioisomeric ratios. Contrary to previous dual-catalytic methods that rely on metal-hydride atom transfer (MHAT) to the olefin prior to carbofunctionalization with a cocatalyst, our mechanistic evidence points toward a nonradical reaction pathway that begins with site-selective carbonickelation across the C═C bond followed by hydride transfer using alkoxide as the hydride source. Utility of the single-catalyst protocol is highlighted through the synthesis of medicinally relevant scaffolds.

Rhodium-Catalyzed Dealkenylative Arylation of Alkenes with Arylboronic Compounds

The C-C bond formation reaction represents a fundamental and important transformation in synthetic chemistry, and exploring new types of C-C bond formation reactions is recognized as appealing, yet challenging. Herein, we disclose the first example of rhodium-catalyzed dealkenylative arylation of alkenes with arylboronic compounds, thereby providing an unconventional access to bi(hetero)aryls with excellent chemoselectivity. In this method, C(aryl)-C(alkenyl) and C(alkenyl)-C(alkenyl) bonds in various alkenes and 1,3-dienes can be cleaved via a hydrometalation and followed by β-carbon elimination pathway for Suzuki-Miyaura reactions. Furthermore, a series of novel organic fluorescent molecules with excellent photophysical properties has been efficiently constructed with this protocol.

Olefin Hydroarylation Catalyzed by a Single-Component Cobalt(-I) Complex

A single-component Co(-I) catalyst, [(PPh₃)₃Co(N₂)]Li(THF)₃, has been developed for olefin hydroarylations with (N-aryl)aryl imine substrates. More than 40 examples were examined under mild reaction conditions to afford the desired alkyl-arene product in good to excellent yields. Catalysis occurs in a regioselective manner to afford exclusively branched products with styrene-derived substrates or linear products for aliphatic olefins. Electron-withdrawing functional groups (e.g., -F, -CF₃, and -CO₂Me) were tolerated under the reaction conditions.

Palladium-Catalyzed Direct C-H Arylation of 3-Butenoic Acid Derivatives

We report herein a direct method to synthesize 4-aryl-3-butenoic acid through a carboxylic-acid-directed oxidative Heck reaction. The various 4-aryl-3-butenoic acids are easily prepared in moderate to good yields. In view of the promising bioactivity of 4-phenyl-3-butenoic acid previously reported, its derivatives reported here may be bioactive.

Synthesis of C3-alkylated benzofurans via palladium-catalyzed regiocontrolled hydro-furanization of unactivated alkenes

A new chelation-controlled hydrofuranization of unactivated olefins with α-alkynyl arylols is reported for the first time, and used to produce a wide range of C₃-alkylated benzofurans with generally good yields under mild conditions.

Enantioselective Alkylamination of Unactivated Alkenes under Copper Catalysis

An enantioselective addition reaction of various alkyl groups to unactivated internal alkenes under Cu catalysis has been developed. The reaction uses amide-linked aminoquinoline as the directing group, 4-alkyl Hantzsch esters as the donor of alkyl radicals, and rarely used biaryl diphosphine oxide as a chiral ligand. β-lactams featuring two contiguous stereocenters at Cβ and the β substituent can be obtained in good yield with excellent enantioselectivity. Mechanistic studies indicate that a nucleophilic addition of the alkyl radical to Cu^II-coordinated alkene is the enantio-determining step.

Anti-selective [3+2] (Hetero)annulation of non-conjugated alkenes via directed nucleopalladation

2,3-Dihydrobenzofurans and indolines are common substructures in medicines and natural products. Herein, we describe a method that enables direct access to these core structures from non-conjugated alkenyl amides and ortho-iodoanilines/phenols. Under palladium(II) catalysis this [3 + 2] heteroannulation proceeds in an anti-selective fashion and tolerates a wide variety of functional groups. N-Acetyl, -tosyl, and -alkyl substituted ortho-iodoanilines, as well as free -NH2 variants, are all effective. Preliminary results with carbon-based coupling partners also demonstrate the viability of forming indane core structures using this approach. Experimental and computational studies on reactions with phenols support a mechanism involving turnover-limiting, endergonic directed oxypalladation, followed by intramolecular oxidative addition and reductive elimination.

Mechanistic Studies of Nickel-Catalyzed Hydroarylation of Styrenes

The mechanism of nickel-catalyzed hydroarylation of styrenes has been explored with density functional theory. Instead of the stepwise pathway via a Ni(II)-H species, computational results unveil that the concerted RO-H oxidative addition/olefin insertion takes place kinetically favorable to generate the alkylnickel(II) species, which further undergoes transmetalation and reductive elimination to yield the hydroarylated product. The origins of regio- and stereoselectivity were revealed via analyzing the electronic and steric effects of the key transition states.

Controlling cyclization pathways in palladium(ii)-catalyzed intramolecular alkene hydro-functionalization via substrate directivity

We report a series of palladium(ii)-catalyzed, intramolecular alkene hydrofunctionalization reactions with carbon, nitrogen, and oxygen nucleophiles to form five- and six-membered carbo- and heterocycles. In these reactions, the presence of a proximal bidentate directing group controls the cyclization pathway, dictating the ring size that is generated, even in cases that are disfavored based on Baldwin's rules and in cases where there is an inherent preference for an alternative pathway. DFT studies shed light on the origins of pathway selectivity in these processes.

We report a series of palladium(ii)-catalyzed, intramolecular alkene hydrofunctionalization reactions with carbon, nitrogen, and oxygen nucleophiles to form five- and six-membered carbo- and heterocycles.

Directed Palladium(II)-Catalyzed Intermolecular Anti-Markovnikov Hydroarylation of Unactivated Alkenes with (Hetero)arylsilanes

We describe herein a regioselective palladium(II)-catalyzed intermolecular hydroarylation of unactivated aliphatic alkenes with electronically and sterically diverse (hetero)arylsilanes under redox-neutral conditions. A removable bidentate 8-aminoquinoline auxiliary was readily employed to dictate the regioselectivity, prevent β-hydride elimination, and facilitate protodepalladation. This silicon-based protocol features a broad substrate scope with excellent functional group compatibility and enables an expeditious route to a variety of γ-aryl butyric acid derivatives in good yields with exclusive anti-Markovnikov selectivity.

Theoretical Insight into Ni(0)-Catalyzed Hydroarylation of Alkenes and Arylboronic Acids

The density functional theory (ωB97XD functional) is employed to clarify nickel(0)/P^tBu₃-catalyzed hydroarylation of alkenes and arylboronic acids with methanol. The computational results reveal that this reaction goes primarily through the ligand-to-ligand H transfer from the O-H bond to the alkene coordinated with nickel, complexation of arylboronic acid to the nickel-alkyl-methoxyl intermediate, attack of methoxyl on boron, transmetalation, and reductive elimination. The formation of the branched 1,1-diarylalkane, linear 1,1-diarylalkane, and alkene-dimer is also discussed in this work.

"Bulky-Yet-Flexible" α-Diimine Palladium-Catalyzed Reductive Heck Cross-Coupling: Highly Anti-Markovnikov-Selective Hydroarylation of Alkene in Air

To pursue a highly regioselective and efficient reductive Heck reaction, a series of moisture- and air-stable α-diimine palladium precatalysts were rationally designed, readily synthesized, and fully characterized. The relationship between the structures of the palladium complexes and the catalytic properties was investigated. It was revealed that the"bulky-yet-flexible"palladium complexes allowed highly anti-Markovnikov-selective hydroarylation of alkenes with (hetero)aryl bromides under aerobic conditions. Further synthetic application of the present protocol could provide rapid and straightforward access to functional and biologically active molecules.