Palladium-Catalyzed Asymmetric Markovnikov Hydroxycarbonylation and Hydroalkoxycarbonylation of Vinyl Arenes: Synthesis of 2-Arylpropanoic Acids

Highly selective and additive-free Pd(OAc)2/CPP catalyzed hydroaminocarbonylation of alkynes

Herein, the synthesis of branched α,β-unsaturated amides by a hydroaminocarbonylation reaction of alkynes with various amine substrates such as aromatic amines, aliphatic amines, solid amine sources like NH4HCO3, and even strongly basic piperidines is reported, using a Pd(OAc)2/hybrid N-heterocyclic carbene-phosphine-phosphine (CPP) catalytic system. The reactions feature no additives, wide substrate scope, high selectivity (b/l > 99 : 1) and excellent yields. Mechanistic studies have disclosed that the reaction takes place via a palladium hydride pathway. CPP adopts a hybrid bidentate ligand conformation with a carbene-phosphine coordination mode, wherein one phosphorus atom remains externally accessible, potentially serving as a stabilizing auxiliary during catalytic cycles.

Palladium-Catalyzed Inward Isomerization Hydroaminocarbonylation of Alkenes

In contrast to the kinetically favored outward isomerization-hydrocarbonylation of alkenes, the disfavored inward isomerization-hydrocarbonylation of alkenes remains an important challenge. Herein, we have developed a novel and effective palladium-catalyzed inward isomerization-hydroaminocarbonylation of unactivated alkenes and aniline hydrochlorides for the formation of synthetically valuable α-aryl carboxylic amides in high yields and high site-selectivities. The high efficiency of the reaction is attributed to a relay catalysis strategy, in which the Markovnikov-favored [PdH]-PtBu3 catalyst is responsible for inward isomerization, while the [PdH]-Ruphos catalyst is responsible for hydroaminocarbonylation of the resulting conjugated aryl alkenes. The reaction exhibits highly functional group tolerance and provides a new method for formal carbonylation of remote C(sp3)-H bond.

Synthesis of Cycloaliphatic Polyamides via Palladium-Catalyzed Hydroaminocarbonylative Polymerization

Polyamides represent one class of materials that is important in modern society. Because of the numerous potential applications of polyamides in various fields, there is a high demand for new polyamide structures, which necessitates the development of new polymerization methods. Herein, we report a novel and efficient palladium-catalyzed hydroaminocarbonylative polymerization of dienes and diamines for the synthesis of cycloaliphatic polyamides. The method employs readily available starting materials, proceeds in an atom-economic manner, and creates a series of new functional polyamides in high yields and high molecular weights. In contrast with the traditional polyamides based on adipic acid, the cycloaliphatic polyamides have superior thermal resistance, higher glass-transition temperature, and better solubility in common organic solvents, thus probably featuring the merits of high-performance and good processability.

Competing Mechanisms in Palladium-Catalyzed Alkoxycarbonylation of Styrene

Palladium-catalyzed carbonylation is a versatile method for the synthesis of various aldehydes, esters, lactones, or lactams. Alkoxycarbonylation of alkenes with carbon monoxide and alcohol produces either saturated or unsaturated esters as a result of two distinct catalytic cycles. The existing literature presents an inconsistent account of the procedures favoring oxidative carbonylation products. In this study, we have monitored the intermediates featured in both catalytic cycles of the methoxycarbonylation of styrene PhCH=CH2 as a model substrate, including all short-lived intermediates, using mass spectrometry. Comparing the reaction kinetics of the intermediates in both cycles in the same reaction mixture shows that the reaction proceeding via alkoxy intermediate [PdII]-OR, which gives rise to the unsaturated product PhCH=CHCO2Me, is faster. However, with an advancing reaction time, the gradually changing reaction conditions begin to favor the catalytic cycle dominated by palladium hydride [PdII]-H and alkyl intermediates, affording the saturated products PhCH2CH2CO2Me and PhCH(CO2Me)CH3 preferentially. The role of the oxidant proved to be crucial: using p-benzoquinone results in a gradual decrease of the pH during the reaction, swaying the system from oxidative conditions toward the palladium hydride cycle. By contrast, copper(II) acetate as an oxidant guards the pH within the 5-7 range and facilitates the formation of the alkoxy palladium complex [PdII]-OR, which favors the oxidative reaction producing PhCH=CHCO2Me with high selectivity. Hence, it is the oxidant, rather than the catalyst, that controls the reaction outcome by a mechanistic switch. Unraveling these principles broadens the scope for developing alkoxycarbonylation reactions and their application in organic synthesis.

Characterization of A π-π stacking cocrystal of 4-nitrophthalonitrile directed toward application in photocatalysis

Photoexcitation of the electron-donor-acceptor complexes have been an effective approach to achieve radicals by triggering electron transfer. However, the catalytic version of electron-donor-acceptor complex photoactivation is quite underdeveloped comparing to the well-established utilization of electronically biased partners. In this work, we utilize 4-nitrophthalonitrile as an electron acceptor to facilitate the efficient π-stacking with electron-rich aromatics to form electron-donor-acceptor complex. The characterization and energy profiles on the cocrystal of 4-nitrophthalonitrile and 1,3,5-trimethoxybenzene disclose that the electron transfer is highly favorable under the light irradiation. This electron acceptor catalyst can be efficiently applied in the benzylic C-H bond photoactivation by developing the Giese reaction of alkylanisoles and the oxidation of the benzyl alcohols. A broad scope of electron-rich aromatics can be tolerated and a mechanism is also proposed. Moreover, the corresponding π-anion interaction of 4-nitrophthalonitrile with potassium formate can further facilitate the hydrocarboxylation of alkenes efficiently.

Catalytic Regio- and Enantioselective Boracarboxylation of Arylalkenes with CO2 and Diboron

Catalytic asymmetric carboxylation of readily available alkenes with CO2, an abundant and sustainable one-carbon building block, that gives access to value-added α-stereogenic carboxylic acids in an atom- and step-economic manner is highly attractive. However, it has remained a formidable challenge for the synthetic community. Here, the first example of Cu-catalyzed highly regio- and enantioselective boracarboxylation reaction on various arylalkenes with diboron under an atmospheric pressure of CO2 is described, which afforded a variety of chiral β-boron-functionalized α-aryl carboxylic acids with up to 87% yield and 97% ee under mild conditions. Importantly, α-substituted arylalkenes could also be subject to this protocol with excellent enantiopurities, thereby rendering an efficient approach for the generation of enantioenriched carboxylic acids with an α-chiral all-carbon quaternary center. Moreover, high functional group tolerance, scalable synthesis, and facile access to bioactive compounds, like (-)-scopolamine, (-)-anisodamine, and (-)-tropicamide, further demonstrated the synthetic utility of this strategy.

Palladium-Catalyzed Difluorocarbene Transfer Enabled Divergent Synthesis of γ-Butenolides and Ynones from Iodobenzene and Terminal Alkynes

Herein, we report a ligand-controlled palladium-catalyzed method that enables the synthesis of ynones and γ-butenolides with excellent regioselectivity from the same set of readily available aryl iodides, aryl acetylenes, and BrCF2CO2K. In this reaction, the [PdII]═CF2 does demonstrate electrophilicity and can generate CO readily when reacting with H2O. It is environmentally friendly and safe compared to traditional methods, and the current protocol enables us to afford ynones and γ-butenolides in high yields with excellent functionality tolerance. Moreover, esters can also be obtained with corresponding phenols and alcohols utilizing this strategy. The success of late-stage functionalization of bioactive compounds further illustrates the synthetic utility of this protocol in material development and drug discovery.

Regiodivergent Carbonylation of Alkenes: Selective Palladium-Catalyzed Synthesis of Linear and Branched Selenoesters

An unprecedented regiodivergent palladium-catalyzed carbonylation of aromatic alkenes has been developed. Utilizing commercially available Pd(CH3 CN)2 Cl2 in the presence of 1,1'-ferrocenediyl-bis(tert-butyl(pyridin-2-yl)phosphine) ligand L8 diverse selenoesters are obtained in a straightforward manner. Key to success for the control of the regioselectivity of the carbonylation step is the concentration of the acidic co-catalyst. This general protocol features wide functional group compatibility and good regioselectivity. Mechanistic studies suggest that the presence of stoichiometric amounts of acid changes the properties and coordination mode of the ligand leading to reversed regioselectivity.

Enantioselective Palladium-Catalyzed Domino Carbonylative Heck Esterification of o-Iodoalkenylbenzenes with Arylboronic Acids

The current investigation presents an innovative palladium-catalyzed asymmetric carbonylative Heck esterification method. This approach facilitates the efficient synthesis of various chiral γ-ketoacid esters by utilizing o-alkenyliodobenzenes and arylboronic acids as primary substrates. This reaction achieves the creation of three carbon-carbon bonds, two carbon-oxygen bonds, and the establishment of a quaternary carbon center within a single step. The α-chiral γ-ketoacid esters were obtained in yields ranging from good to high yields, displaying enantiomeric excesses (ee's) levels up to 92% under mild reaction conditions.

Palladium-catalyzed regiodivergent hydrochlorocarbonylation of alkenes for formation of acid chlorides

Novel strategy for acid chlorides formation that do not use carboxylic acids is particularly attractive in chemical synthesis but remains challenging. Herein, we reported the development of a highly effective Pd-catalyzed hydrochlorocarbonylation of alkenes with CO for the formation of alkyl acid chlorides. Chlorosilane and AcOH were found as a mild HCl source for the reaction. The reaction shows broad substrate scope and produces both branched and linear alkyl acid chlorides in good to high yields upon different ligands and solvents. Cooperating with follow-up acylation reactions, the Pd-catalyzed hydrochlorocarbonylation offers a complementary platform for the synthesis of diverse carbonyl compounds from alkenes. Mechanistic investigations suggested that the reaction proceeded though a palladium hydride pathway, and CO prompted reductive elimination of the acyl-Pd-Cl intermediate.

Regioselective hydroesterification of alkenes and alkenylphenols utilizing CO2 and hydrosilane

As an important and attractive C1 building block, the diversified exploitation of CO₂ in chemical transformations possesses significant research and application value. Herein, an effective palladium-catalyzed intermolecular hydroesterification of a wide range of alkenes with CO₂ and PMHS is described, successfully generating diverse esters with up to 98% yield and up to 100% linear-selectivity. In addition, the palladium-catalyzed intramolecular hydroesterification of alkenylphenols with CO₂ and PMHS is also developed to construct a variety of 3-substituted-benzofuran-2(3H)-ones with up to 89% yield under mild conditions. In both systems, CO₂ functions as an ideal CO source with the assistance of PMHS, thus smoothly participating in a series of alkoxycarbonylation processes.

C(alkyl)-C(vinyl) bond cleavage enabled by Retro-Pallada-Diels-Alder reaction

Activation and cleavage of carbon-carbon (C-C) bonds is a fundamental transformation in organic chemistry while inert C-C bonds cleavage remains a long-standing challenge. Retro-Diels-Alder (retro-DA) reaction is a well-known and important tool for C-C bonds cleavage but less been explored in methodology by contrast to other strategies. Herein, we report a selective C(alkyl)-C(vinyl) bond cleavage strategy realized through the transient directing group mediated retro-Diels-Alder reaction of a six-membered palladacycle, which is obtained from an in situ generated hydrazone and palladium hydride species. This unprecedented strategy exhibits good tolerances and thus offers new opportunities for late-stage modifications of complex molecules. DFT calculations revealed that an intriguing retro-Pd(IV)-Diels-Alder process is possibly involved in the catalytic cycle, thus bridging both Retro-Diels-Alder reaction and C-C bond cleavage. We anticipate that this strategy should prove instrumental for potential applications to achieve the modification of functional organic skeletons in synthetic chemistry and other fields involving in molecular editing.

Pd-Catalyzed Asymmetric 5-exo-trig Cyclization/Cyclopropanation/Carbonylation of 1,6-Enynes for the Construction of Chiral 3-Azabicyclo[3.1.0]hexanes

We herein disclose a mild and efficient access to chiral 3-azabicyclo[3.1.0]hexanes via a Pd-catalyzed asymmetric 5-exo-trig cyclization/cyclopropanation/carbonylation of 1,6-enynes. Various nucleophiles, such as alcohols, phenols, amines and water, are well compatible with the reaction system. This reaction forms three C-C bonds, two rings, two adjacent quaternary carbon stereocenters as well as one C-O/C-N bond with excellent regio- and enantioselectivities. The products could be further functionalized to generate a library of 3-azabicyclo[3.1.0]hexane frameworks.

Nickel-Catalyzed Enantioconvergent Carboxylation Enabled by a Chiral 2,2'-Bipyridine Ligand

In contrast to previous approaches to chiral α-aryl carboxylic acids that based on reactions using hazardous gases, pressurized setup and mostly noble metal catalysts, in this work, a nickel-catalyzed general, efficient and highly enantioselective carboxylation reaction of racemic benzylic (pseudo)halides under mild conditions using atmospheric CO₂ has been developed. A unique chiral 2,2'-bipyridine ligand named Me-SBpy featuring compact polycyclic skeleton enabled both high reactivity and stereoselectivity. The utility of this method has been demonstrated by synthesis of various chiral α-aryl carboxylic acids (30 examples, up to 95 % yield and 99 : 1 er), including profen family anti-inflammatory drugs and transformations using the acids as key intermediates. Based on mechanistic experimental results, a plausible catalytic cycle involving Ni-complex/radical equilibrium and Lewis acid-assisted CO₂ activation has been proposed.

Catalytic direct hydrocarboxylation of styrenes with CO2 and H2

A three-component hydrocarboxylation of an olefin with CO₂ and H₂ could be regarded as a dream reaction, since it would provide a straightforward approach for the synthesis of aliphatic carboxylic acids in perfect atom economy. However, this transformation has not been realized in a direct manner under mild conditions, because boosting the carboxylation with thermodynamically stable CO₂ while suppressing the rapid hydrogenation of olefin remains a challenging task. Here, we report a rhodium-catalysed reductive hydrocarboxylation of styrene derivatives with CO₂ and H₂ under mild conditions, in which H₂ served as the terminal reductant. In this approach, the carboxylation process was largely accelerated by visible light irradiation, which was proved both experimentally and by computational studies. Hydrocarboxylation of various kinds of styrene derivatives was achieved in good yields without additional base under ambient pressure of CO₂/H₂ at room temperature. Mechanistic investigations revealed that use of a cationic rhodium complex was critical to achieve high hydrocarboxylation selectivity.

Pd-Catalyzed Enantioselective Hydroamidocarbonylation of α-Substituted Acrylamides to Chiral Succinimides

With the aid of an innate amide group, an intramolecular Pd-catalyzed enantioselective hydroamidocarbonylation reaction of α-substituted acrylamides was developed, and a series of chiral 2-substituted succinimides were obtained in moderate to high yields and enantioselectivities. The generality of this approach was demonstrated by the carbonylation of both aryl- and alkyl-substituted acrylamides containing numerous functional groups.

Progress on transition metal catalyzed asymmetric hydroesterification, hydrocarboxylation, and hydroamidation reactions of olefins

Hydrocarboxylation, hydroesterification, and hydroamidation of olefins are fundamental transformations in organic synthesis. Asymmetric processes for these transformations provide an effective and straightforward approach to optically active carboxylic acids and their derivatives, which are highly useful compounds in pharmaceuticals, materials, fine chemicals, etc. This review provides a brief summary of the development of asymmetric hydroesterification, hydrocarboxylation, and hydroamidation with CO and its surrogates.

Palladium-Catalyzed Asymmetric Dearomative Carbonylation of Indoles

Herein, we disclose a strategy for the asymmetric dearomatization of N-arylacyl indoles via a palladium-catalyzed tandem Heck/carbonylation, leading to an array of indoline-3-carboxylates bearing vicinal C2-aza-quaternary and C3 tertiary stereocenters in high yields and excellent enantio- and diastereoselectivities. This study is an important advance in the field of asymmetric carbonylation and enantioselective dearomatization reactions.

Ligand-enabled palladium-catalyzed hydroesterification of vinyl arenes with high linear selectivity to access 3-arylpropanoate esters

Palladium-catalyzed linear-selective hydroesterification of vinyl arenes with alcohols enabled by diphosphine ligands derived from bis[2-(diphenylphosphino)ethyl]amides has been developed. A variety of 3-arylpropanoate esters were obtained in high yields and regioselectivity. The robustness of this methodology was further demonstrated by the efficient gram-scale synthesis of the ethyl 3-phenylpropanoate as a precursor to hydrocinnamic acid.

Enantioselective Synthesis of Chiral Carboxylic Acids from Alkynes and Formic Acid by Nickel-Catalyzed Cascade Reactions: Facile Synthesis of Profens

We report a stereoselective conversion of terminal alkynes to α-chiral carboxylic acids using a nickel-catalyzed domino hydrocarboxylation-transfer hydrogenation reaction. A simple nickel/BenzP* catalyst displayed high activity in both steps of regioselective hydrocarboxylation of alkynes and subsequent asymmetric transfer hydrogenation. The reaction was successfully applied in enantioselective preparation of three nonsteroidal anti-inflammatory profens (>90 % ees) and the chiral fragment of AZD2716.

endo-5-Norbornene-2,3-dimethanol-promoted asymmetric Heck/Suzuki cascade reaction of N-(2-bromophenyl)acrylamides

An endo-5-norbornene-2,3-dimethanol-promoted highly enantioselective palladium-catalyzed Heck/Suzuki cascade reaction of N-(2-bromophenyl)acrylamides has been developed.

Studies on Pd-Catalyzed Asymmetric Hydroesterification of Enimides. A Possible Approach to Optically Active β-Amino Acid Derivatives

A Pd-catalyzed asymmetric hydroesterification of enimides with phenyl formate is described. A DIOP-based system has been found to be highly active catalyst, giving the corresponding β-amino esters with up to...

Palladium-Catalyzed Regio- and Chemoselective Double-Alkoxycarbonylation of 1,3-Diynes: A Computational Study

The palladium-catalyzed double-alkoxycarbonylation of 1,3-diynes provides an efficient approach for the selective synthesis of 1,2,3,4-tetrasubstituted conjugated dienes. In this report, density functional theory calculations have been performed to elucidate the...

Nickel-Catalyzed Reductive Cross-Coupling of Aryl Bromides with Vinyl Acetate in Dimethyl Isosorbide as a Sustainable Solvent

A nickel-catalyzed reductive cross-coupling has been achieved using (hetero)aryl bromides and vinyl acetate as the coupling partners. This mild, applicable method provides a reliable access to a variety of vinyl arenes, heteroarenes, and benzoheterocycles, which should expand the chemical space of precursors to fine chemicals and polymers. Importantly, a sustainable solvent, dimethyl isosorbide, is used, making this protocol more attractive from the point of view of green chemistry.

Diastereoselective Alkene Hydroesterification Enabling the Synthesis of Chiral Fused Bicyclic Lactones

Palladium-catalysed diastereoselective hydroesterification of alkenes assisted by the coordinative hydroxyl group in the substrate afforded a variety of chiral γ-butyrolactones bearing two stereocenters. Employing the carbonylation-lactonization products as the key intermediates, the route from the alkenes with single chiral center to chiral THF-fused bicyclic γ-lactones containing three stereocenters was developed.

Catalytic asymmetric synthesis of α-stereogenic carboxylic acids: recent advances

Chiral carboxylic acids bearing an α-stereogenic center constitute the backbone of many natural products and therapeutic reagents as well as privileged chiral ligands and catalysts. Hence, it is not surprising that a large number of elegant catalytic asymmetric strategies have been developed toward the efficient synthesis of α-chiral carboxylic acids, such as α-hydroxy acids and α-amino acids. In this review, the recent advances in asymmetric synthesis of α-stereogenic free carboxylic acids via organocatalysis and transition metal catalysis are summarized (mainly from 2010 to 2020). The content is organized by the reaction type of the carboxyl source involved, including asymmetric functionalization of substituted carboxylic acids, cyclic anhydrides, α-keto acids, substituted α,β-unsaturated acids and so on. We hope that this review will motivate further interest in catalytic asymmetric synthesis of chiral α-substituted carboxylic acids.

Copper-Catalyzed Ullmann-Type Coupling and Decarboxylation Cascade of Arylhalides with Malonates to Access α-Aryl Esters

We have developed a high-efficiency and practical Cu-catalyzed cross-coupling to directly construct versatile α-aryl-esters by utilizing readily available aryl bromides (or chlorides) and malonates. These gram-scale approaches occur with turnovers of up to 1560 and are smoothly conducted by the usage of a low catalyst loading, a new available ligand, and a green solvent. A variety of functional groups are tolerated, and the application occurs with α-aryl-esters to access nonsteroidal anti-inflammatory drugs (NSAIDs) on the gram scale.

Lipase Assisted (S)-Ketoprofen Resolution from Commercially Available Racemic Mixture

Ketoprofen is a commercially available drug sold as a racemic mixture that belongs to the family of non-steroidal anti-inflammatory drugs known as profens. It has been demonstrated (in vitro) that (S)-ketoprofen is around 160 times more potent than its enantiomer (R)-ketoprofen, while accumulation of (R)-ketoprofen can cause serious side effects, such as dyspepsia, gastrointestinal ulceration/bleeding, pain, salt and fluid retention, and hypertension. In this work, four commercially available lipases were systematically assessed. Parameters such as conversion, enantiomeric excess, and enantioselectivity were considered. Among them, and by evaluating lipase load, temperature, solvent, and alcohol, Candida rugosa lipase exhibited the best results in terms of enantioselectivity E = 185 ((S)-enantiopreference) with esterification conversions of c = 47% (out of 50%) and enantiomeric excess of 99%. The unreacted (R)-enantiomer was recovered by liquid-liquid extraction and racemized under basic media, which was recycled as starting material. Finally, the (S)-alkyl ketoprofen ester was successfully enzymatically hydrolyzed to the desired (S)-ketoprofen with c = 98.5% and 99% ee. This work demonstrated the benefit and efficiency of using Candida rugosa lipase to kinetically resolve racemic ketoprofen by an environmentally friendly protocol and with the recycling of the undesired (R)-ketoprofen.