Palladium(II)-catalyzed alkene functionalization via nucleopalladation: stereochemical pathways and enantioselective catalytic applications

π-Lewis Base Activation of Carbonyls and Hexafluorobenzene

We report hitherto elusive side-on η2-bonded palladium(0) carbonyl (anthraquinone, benzaldehyde) and arene (benzene, hexafluorobenzene) palladium(0) complexes and present the catalytic hydrodefluorination of hexafluorobenzene by cyclohexene. The comparison with respective cyclohexene, pyridine and tetrahydrofuran complexes reveals that the experimental ligand binding strengths follow the order THF Collapse

Key Words

• Catalysis
• Chemical Bonding
• Intermediates
• Organometallic Chemistry
• Spectroscopy

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MESH Headings Collapse

Grants

• 948185 H2020 European Research Council
• 256/506-1 Deutsche Forschungsgemeinschaft
• 256/582-1 Deutsche Forschungsgemeinschaft
• 440719683 Deutsche Forschungsgemeinschaft
• 2008-390540038 Deutsche Forschungsgemeinschaft

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Affiliation(s)

Aditesh Mondal Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany
Kevin Breitwieser Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany
Sergi Danés Departament de Química, Institut de Química Computacional I Catàlisi, Universitat de Girona, c/m. Aurelia Capmany 69, 17003, Girona, Spain
Annette Grünwald Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany Inorganic and General Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, D-91058, Erlangen, Germany
Frank W Heinemann Inorganic and General Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, D-91058, Erlangen, Germany
Bernd Morgenstern Solid State Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany
Frank Müller Experimental Physics and Center for Biophysics, Saarland University, Campus E2.9, D-66123, Saarbrücken, Germany
Michael Haumann Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany
Maximilian Schütze Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany
Dustin Kass Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany
Kallol Ray Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany
Dominik Munz Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany

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Asymmetric Amplification in Oxypalladation/Malononitrile Addition Cascade Enabled by Heterochiral-Assembly of Products

An enantioselective oxypalladation/malononitrile addition cascade reaction of alkyne-tethered malononitriles was reported to synthesize enaminones bearing an all-carbon quaternary center. Using Pd(TFA)2/Pyox as a precatalyst, an array of enaminone products were obtained in moderate overall yields, with excellent er (93.5:6.5-99.5:0.5) in solution phase and nearly racemic in solid phase. The usage of 3,5-dinitrobenzoic acid as the nucleophile was proven to be crucial to this significant chiral amplification due to a heterochiral self-assembly of the products through an intermolecular multiple π-π stacking interaction. A strong positive nonlinear effect (NLE) was observed in solution phase, which was further highlighted by the access to an enantiopure enaminone (99.5:0.5 er) even using a partially enantiopure catalyst (54:46 er).

Ni-catalyzed regioselective and site-divergent reductive arylalkylations of allylic amines

Catalytic methods by switching the least parameters for regioselective and site-divergent transformations to construct different architectures from identical and readily available starting materials are among the most ideal catalytic protocols. However, the associated challenge to precisely control both regioselectivity and site diversity renders this strategy appealing yet challenging. Herein, Ni-catalyzed cross-electrophile regioselective and site-divergent 1,2- and 1,3-arylalkylations of N-acyl allylic amines have been developed. This Ni-catalyzed reductive three-component protocol enables 1,2-arylalkylation and 1,3-arylalkylation of allylic amines with aryl halides and alkyl halides with excellent chemo-, regio- and site-selectivity, representing the first example of controlled migratory difunctionalization of alkenes under reductive conditions. A wide range of terminal and internal unactivated allylic amines, aryl halides and alkyl precursors were tolerated, providing straightforward and efficient access to diverse C(sp3)-rich branched aliphatic amines from identical starting materials.

Ruthenium-catalyzed three-component tandem remote C-H functionalization of naphthalenes: modular and concise synthesis of multifunctional naphthalenes

The prevalence of naphthalene compounds in biologically active natural products, organic ligands and approved drugs has motivated investigators to develop efficient strategies for their selective synthesis. C-H functionalization of naphthalene has been frequently deployed, but mainly involves two-component reactions, while multiple-component C-H functionalization for the synthesis of naphthalene compounds has thus far proven elusive. Herein, we disclose a versatile three-component protocol for the modular synthesis of multifunctional naphthalenes from readily available simple naphthalenes, olefins and alkyl bromides via P(iii)-assisted ruthenium-catalyzed remote C-H functionalization. This protocol not only tolerates various functional groups, but can be applied to many natural product and drug derivatives, and can involve a three-component reaction with two different bioactive molecules. Mechanism studies indicated that the utilization of tertiary phosphines as auxiliary groups is the key to achieving the three-component free-radical reaction.

Enantioselective construction of silicon-stereogenic vinylsilanes from simple alkenes

The diverse utility of acyclic vinylsilanes has driven the interest in the synthesis of enantioenriched vinylsilanes bearing a Si-stereogenic center. However, the predominant approaches for catalytic asymmetric generation of Si-stereogenic vinylsilanes have mainly relied on transition metal-catalyzed reactions of alkynes with different silicon sources. Here we successfully realize the enantioselective synthesis of linear silicon-stereogenic vinylsilanes with good yields and enantiomeric ratios from simple alkenes under rhodium catalysis. The significance of this transformation lies in its ability to achieve regioconvergent and enantioconvergent conversion, efficiently transforming petroleum-derived isomeric mixtures of olefin feedstocks into a single regio- and stereoisomer product. The practicality of this method is further exemplified by the diverse downstream transformations of these enantioenriched silicon-stereogenic vinylsilanes leveraging the olefin functionality and the leaving group nature of the aryl substituent on silicon as well as the development of chiral π-conjugated double bond systems.

Chemoselectivity in Pd-Based Dyotropic Rearrangement: Development and Application in Total Synthesis of Pheromones

In the dyotropic rearrangement of molecules with semiflexible structures, characterized by a freely rotating static C-C bond, the formation of a mixture of products is common due to the coexistence of several energetically comparable conformers. Herein, we report that it is possible to modulate the shifting groups by adjusting the metal's coordination sphere in Pd-based dyotropic rearrangement. In the presence of a catalytic amount of Pd(II) salt, the reaction of γ-hydroxyalkenes or γ,δ-dihydroxyalkenes with Selectfluor affords fluorinated tetrahydropyranols or 6,8-dioxabicyclo[3.2.1]octanes (DOBCO), respectively. In this domino process, two C(sp2) and one allylic C(sp3) are sequentially activated and functionalized through a pivotal conformation-controlled chemoselective C(sp3)-C(sp3) and C(sp3)-Pd(IV) bond metathesis reaction. Mechanistic studies suggest a reaction sequence including 5-exo-trig oxypalladation, Pd oxidation, and chemoselective ring expansion 1,2-Csp3/Pd(IV) dyotropic rearrangement, followed by hydroxypalladation of in situ generated dihydropyrans. These findings provide a unique retrosynthetic disconnection for the synthesis of 6,8-DOBCO. We showcase its potential by developing a concise synthesis of three important pheromones. Notably, (+)-frontalin is synthesized from a commercially available 1,5-diene in only two steps, utilizing Sharpless catalytic asymmetric dihydroxylation and Pd-catalyzed domino cyclization developed in this study.

Photocatalytic Alkene-Migrative Chain Elongation of 2-Phosphinostyrenes with Aldehydes

The photocatalytic alkene-migrative chain elongation reaction of 2-phosphinostyrenes with aldehydes under mild conditions in response to blue light was demonstrated. A broad range of aldehydes, both aliphatic and aromatic, participated in this reaction to afford alkene-phosphine oxides in a Z-selective manner. Mechanistic experiments suggested the formation of benzophospholene-based ylide intermediates via photocatalytic cyclization of phosphinostyrenes followed by solvent-mediated proton transfer under base-free reaction conditions.

Pd-Catalyzed Migratory 1,1-Cycloannulation Reaction of Alkenes

Here, we report a novel strategy for the preparation of diverse heterocycles via a Pd-catalyzed migratory 1,1-cycloannulation reaction (MCAR) of alkenes. Starting from readily available alkenyl amines and alkenyl alcohols, this approach allows the formation of a wide range of five- to seven-membered azaheterocycles and oxaheterocycles with high efficiency and good functional group tolerance. The key to the realization of this reaction is the use of 4-iodophenol or 2-iodophenol derivatives where the phenolic hydroxyl group plays a critical role in controlling the direction of migration and the ring-size of the heterocycles through the formation of a quinone methide intermediate.

Copper-Catalyzed Cycloaddition/Coupling Cascades of Azomethine Imines with Alkynes for Divergent Synthesis of (Z)-Alkenyl and Alkynyl N,N'-Bicyclic Pyrazolidinones

Copper-catalyzed cycloaddition/coupling cascades utilizing azomethine imines and alkynes have been developed for the divergent synthesis of (Z)-alkenyl and alkynyl N,N'-bicyclic pyrazolidinones by varying the reaction conditions. The choice of inert or oxidative atmosphere plays a crucial role in determining the transformation pathways. These reactions have broad substrate scopes and mild conditions, making them potentially useful.

Alkyl Sulfonium Salts Enabled Radical Thiocyanohydroxylation of Alkenes

Herein, we report a novel and practical strategy for alkyl sulfonium salts mediating radical thiocyanohydroxylation of alkenes. This reaction features metal-free and mild conditions, generation of noncarbon radicals from the readily available alkyl sulfonium salts, easy handling, and excellent functional group compatibility. A diverse range of activated and unactivated alkenes worked well to deliver various β-thiocyanato alcohols.

Hydroalkylation of unactivated olefins with C(sp3)─H compounds enabled by NiH-catalyzed radical relay

The hydroalkylation reaction of olefins with alkanes is a highly desirable synthetic transformation toward the construction of C(sp3)─C(sp3) bonds. However, such transformation has proven to be challenging for unactivated olefins, particularly when the substrates lack directing groups or acidic C(sp3)─H bonds. Here, we address this challenge by merging NiH-catalyzed radical relay strategy with a HAT (hydrogen atom transfer) process. In this catalytic system, a nucleophilic alkyl radical is generated from a C(sp3)─H compound in the presence of a HAT promotor, which couples with an alkyl metallic intermediate generated from the olefin substrate with a NiH catalyst to form the C(sp3)─C(sp3) bond. Starting from easily available materials, the reaction not only demonstrates wide functional group compatibility but also provides hydroalkylation products with regiodivergence and excellent enantioselectivity through effective catalyst control under mild conditions.

Paired electrocatalysis enabled oxidative coupling of styrenes with alkyl radicals

A paired electrocatalysis strategy for intermolecular oxidative cross-dehydrocoupling between styrenes and ethers or p-methylphenol derivatives using ketone as a mild oxidant is described. This approach enables the generation of Csp3 carbon-centered radicals through anodic oxidation, followed by reductive coupling of ketones at the cathode, ultimately yielding valuable oxidative alkylation products.

Photooxidative C-C double bond cleavage of β-enaminocarbonyl compounds: toward selective N-formylation of amines

A photooxidative C-C double bond cleavage of electron-deficient β-enaminocarbonyl compounds possessing a silyl group at the α-position to the nitrogen atom using methylene blue (MB) as the photosensitizer was explored. Photochemically generated 1O2 was added across the CC bond with the aid of a tethered silyl group to cleave it and form N-formylamines. This reaction protocol exhibited compatibility with numerous β-enaminocarbonyl substrates, including those with various N-alkyl, N-benzyl and N-aryl substituents.

Regioselective intermolecular carboamination of allylamines via nucleopalladation: empowering three-component synthesis of vicinal diamines

An intermolecular carboamination reaction of allyl amines under Pd(ii)-catalysis is reported, expediting the synthesis of valuable vicinal diamines embedded in a functionally enriched linear carbon framework with high yields and exclusive Markovnikov selectivity. Central to our approach is the strategic use of a removable picolinamide auxiliary, which directs the regioselectivity during aminopalladation and stabilizes the crucial 5,5-palladacycle intermediate. This stabilization facilitates oxidative addition to carbon electrophiles, enabling the simultaneous incorporation of diverse aryl/styryl groups as well as important amine motifs, such as sulfoximines and anilines, across carbon-carbon double bonds. The protocol features broad substrate compatibility, tolerance to various functional groups, and scalability. The utility of this method is further demonstrated by the site-selective diversification of pharmaceutical agents. Additionally, these products serve as versatile intermediates for synthesizing heterocycles and function as effective ligands in catalytic transfer hydrogenation reactions. Notably, this work represents a rare instance of nucleopalladation-guided intermolecular carboamination of allylamines.

Synthesis of γ-Amino Amides by Iridium-Catalyzed Enantioselective Hydroamination of Internal Alkenes Directed by an Amide

Catalytic regio- and enantioselective hydroamination of less activated internal alkenes presents a challenge to synthetic chemists due to their low reactivity and the difficulty in simultaneously controlling regio- and enantioselectivities. Here, we report an iridium-catalyzed enantioselective hydroamination of internal alkenes directed by an amide. The amide group on the alkene effectively directs the catalyst to overcome the low reactivity and control the regioselectivity and the enantiotopic face selection. Phthalimide serves as the amination agent, which could be readily removed to afford a primary amine. This coordination assistance enables hydroamination to occur selectively at the remote position with up to 97 % ee, delivering valuable enantio-enriched γ-amino acid derivatives that are otherwise challenging to access.

Cu-Catalyzed Asymmetric Three-Component Radical Acylarylation of Vinylarenes with Aldehydes and Aryl Boronic Acids

The direct use of readily available aldehydes as acyl radical precursors has facilitated diverse three-component acylative difunctionalization reactions of alkenes, offering a powerful route to synthesize β-branched ketones. However, asymmetric three-component acylative difunctionalization of alkenes with aldehydes still remains elusive. Here we report a copper-catalyzed asymmetric three-component radical acylarylation of vinylarenes with aldehydes and aryl boronic acids. This method begins with acyl radical formation from an aldehyde via hydrogen atom transfer. The acyl radical adds to the alkene, forming a new benzylic radical that then undergoes copper-catalyzed enantioselective arylation. A chiral binaphthyl-tethered bisoxazoline ligand is essential for achieving high stereocontrol. This strategy enables the direct synthesis of a range of synthetically valuable chiral β,β-diaryl ketones from aldehydes and vinylarenes.

Copper-Catalyzed 1,3-Aminocyclization of Cyclopropanes as a Rapid Entry to γ-Amino Heterocycles

We herein report a copper-catalyzed 1,3-aminocyclization of cyclopropanes as a direct and versatile entry into important heterocycles. This reaction was initiated by a copper-catalyzed, NFSI-promoted ring opening of cyclopropanes, followed by nucleophilic cyclization. A variety of nucleophiles successfully participate in this transformation, including alcohols, carboxylic acids, sulfonamides, and amides, for the construction of diverse cyclic ethers, pyrrolidines, lactones, and iminolactones.

Strategies for arene dissociation from transition metal η6-arene complexes

Transition metal η6-arene complexes have unique properties that facilitate a variety of arene substitution reactions, rendering π-activation a powerful approach for arene functionalization. For decades, these complexes have been studied in the context of coordination chemistry and synthetic methodology via stoichiometric reactivity; one central challenge in expanding the utility of arene functionalization via transition-metal-π-activation is the dissociation of the arene product that remains bound to the transition metal. In this perspective, we highlight representative strategies and methods for the removal and/or exchange of arenes from such complexes. Recent studies that implement these strategies toward catalytic processes are discussed, along with remaining challenges in this area.

KBr-Mediated Electrochemical Dihydroxylation of Alkenes Using H2O as the Hydroxyl Source

Dihydroxylation of alkenes provides direct access to vicinal diols. Herein, a new electrochemical strategy for dihydroxylation of alkenes in only the presence of KBr is disclosed. Water serves as a green and sustainable hydroxyl source. Cheap KBr acts as both an electrolyte and a catalyst. Both styrenes and unactivated alkenes proceed in the dihydroxylation reactions smoothly to furnish vicinal diols in good yields. The successful synthesis of Cyclandelate, DTD derivative precursors, and a key intermediate for the synthesis of herbicide Metamitron highlights its synthetic utility.

Visible-Light-Mediated Trifluoroalkylation of Isoquinolines via Three-Component Minisci-Type Reaction

A sustainable photocatalytic approach has been established for trifluoroalkylation of isoquinoline via a three-component Minisci-type reaction using a green solvent. The polarity reversal radical cascade strategy renders the selective addition of an electrophilic CF3 radical to an olefin to forge a nucleophilic C-centered radical. This multicomponent approach is operationally simple and environmentally benign with various functional groups, viz. aldehydes, acetals, amides, and halides. Mechanistic investigations were carried out to elaborate the reductive quenching catalytic pathway.

Photocatalytic Multisite Functionalization of Unactivated Terminal Alkenes by Merging Polar Cycloaddition and Radical Ring-Opening Process

Although highly appealing for rapid access of molecular complexity, multi-functionalization of alkenes that allows incorporation of more than two functional groups remains a prominent challenge. Herein, we report a novel strategy that merges dipolar cycloaddition with photoredox promoted radical ring-opening remote C(sp3)-H functionalization, thus enabling a smooth 1,2,5-trifunctionalization of unactivated alkenes. A highly regioselective [3+2] cycloaddition anchors a reaction trigger onto alkene substrates. The subsequent halogen atom transfer (XAT) selectively initiates ring-opening process, which is followed by a series of 1,5-hydrogen atom transfer (1,5-HAT) and intermolecular fluorine atom transfer (FAT) events. With this method, site-selective introduction of three different functional groups is accomplished and a broad spectrum of valuable β-hydroxyl-ϵ-fluoro-nitrile products are synthesized from readily available terminal alkenes.

Metal-Carbon Bond Heterolysis Energy Scale for Model Palladium Catalysts

Thermodynamic studies of transition-metal intermediates are crucial for understanding of metal-catalyzed transformations. Herein, a series of arylpalladium cyanomethanides were synthesized and characterized. Their palladium-carbon bond heterolysis energies (ΔGhet(Pd-C)) were determined in DMSO for the first time by equilibrium methods. ΔGhet(Pd-C) values of 7.9-19.1 kcal/mol, located between the ΔGhet(Pd-O) and ΔGhet(Pd-N) scales previously established, are much smaller than the corresponding ΔGhet(C-H)s of phenylacetonitrile (30.0 kcal/mol). Linear free energy relationship (LEFR) analysis reveals insights into the structure-property relationship and the factor dictating the thermodynamics of metalation. These ΔGhet(Pd-X)s in combination with ΔGhet(X-H)s are successfully used to diagnose the reaction feasibility and selectivity of X-H bond activation.

Radical-triggered translocation of C-C double bond and functional group

Multi-site functionalization of molecules provides a potent approach to accessing intricate compounds. However, simultaneous functionalization of the reactive site and the inert remote C(sp3)-H poses a formidable challenge, as chemical reactions conventionally occur at the most active site. In addition, achieving precise control over site selectivity for remote C(sp3)-H activation presents an additional hurdle. Here we report an alternative modular method for alkene difunctionalization, encompassing radical-triggered translocation of functional groups and remote C(sp3)-H desaturation via photo/cobalt dual catalysis. By systematically combining radical addition, functional group migration and cobalt-promoted hydrogen atom transfer, we successfully effectuate the translocation of the carbon-carbon double bond and another functional group with precise site selectivity and remarkable E/Z selectivity. This redox-neutral approach shows good compatibility with diverse fluoroalkyl and sulfonyl radical precursors, enabling the migration of benzoyloxy, acetoxy, formyl, cyano and heteroaryl groups. This protocol offers a resolution for the simultaneous transformation of manifold sites.

Nickel-Catalyzed Enantioselective Reductive N-Cyclization-Thiolation Reaction of Alkene-Tethered Oxime Esters and Disulfides

Asymmetric aza-Heck cyclization and coupling reactions offer efficient access to enantioenriched N-heterocycles, yet the current studies focus primarily on sequential C-N and C-C bond formation. Herein, we report an enantioselective reductive aza-Heck cyclization followed by a C-S coupling sequence, ultimately yielding sulfide-containing enantioenriched pyrrolines. The reaction is conducted under mild conditions and tolerates broad functionalities including alkynes, phenols, anilines, amides, nitriles, and bromides.

Pd/Cu-Cocatalyzed Enantio- and Diastereodivergent Wacker-Type Dicarbofunctionalization of Unactivated Alkenes

The Wacker and Wacker-type reactions are some of the most fundamental and powerful transformations in organic chemistry for their ability to efficiently produce valuable chemicals. Remarkable progress has been achieved in asymmetric oxy/aza-Wacker-type reactions; however, asymmetric Wacker-type dicarbofunctionalization remains underdeveloped, especially for the concurrent construction of two stereocenters. Herein, we report a Pd/Cu-cocatalyzed enantio- and diastereodivergent Wacker-type dicarbofunctionalization of alkene-tethered aryl triflates with imino esters. A series of 2-indanyl motifs bearing adjacent carbon stereocenters could be easily synthesized in moderate to excellent yields and with good to excellent diastereo- and enantioselectivities (up to >20:1 dr and >99% ee). Density functional theory calculations revealed that the origin of diastereoselectivity in this Pd/Cu synergistic catalytic system is jointly determined by both the intermolecular anti-carbopalladation of alkenes and the reductive elimination processes, in accordance with the Curtin-Hammett principle.

Enantioselective Aminosilylation of Alkenes by Palladium/Ming-Phos-Catalyzed Tandem Narasaka-Heck/Silylation Reaction

A Pd-catalyzed enantioselective aminosilylation of alkenes via tandem Aza-Heck/silylation reaction under Pd/Sadphos catalysis is disclosed. A wide array of oxime esters and silicon reagents are tolerated, furnishing the chiral pyrrolines bearing one quaternary or two contiguous stereocenters in good yield with high enantioselectivity. Not only terminal alkenes but also tri-substituented internal alkenes successfully participate in the reaction, delivering vicinal stereocenters in complete diastereoselectivity and high enantioselectivity. DFT study is conducted to probe the reaction pathway and the origin of the enantioselectivity, which revealed that the stereoinduction arises from the weak interaction between the aromatic ring of the substrate fragment and naphthyl group in the ligand.

Catalytic asymmetric synthesis of meta benzene isosteres

Although aromatic rings are common elements in pharmaceutically active compounds, the presence of these motifs brings several liabilities with respect to the developability of a drug1. Nonoptimal potency, metabolic stability, solubility and lipophilicity in pharmaceutical compounds can be improved by replacing aromatic rings with non-aromatic isosteric motifs2. Moreover, whereas aromatic rings are planar and lack three-dimensionality, the binding pockets of most pharmaceutical targets are chiral. Thus, the stereochemical configuration of the isosteric replacements may offer an added opportunity to improve the affinity of derived ligands for target receptors. A notable impediment to this approach is the lack of simple and scalable catalytic enantioselective syntheses of candidate isosteres from readily available precursors. Here we present a previously unknown palladium-catalysed reaction that converts hydrocarbon-derived precursors to chiral boron-containing nortricyclanes and we show that the shape of these nortricyclanes makes them plausible isosteres for meta disubstituted aromatic rings. With chiral catalysts, the Pd-catalysed reaction can be accomplished in an enantioselective fashion and subsequent transformation of the boron group provides access to a broad array of structures. We also show that the incorporation of nortricyclanes into pharmaceutical motifs can result in improved biophysical properties along with stereochemistry-dependent activity. We anticipate that these features, coupled with the simple, inexpensive synthesis of the functionalized nortricyclane scaffold, will render this platform a useful foundation for the assembly of new biologically active agents.

Pd-catalyzed Markovnikov selective oxidative amination of 4-pentenoic acid

Pd-catalyzed regioselective amination of unactivated alkene remains a challenge and is of great interest. Herein, a palladium-catalyzed and ligand-controlled strategy for the Markovnikov selective oxidative amination of 4-pentenoic acid has been described. The protocol effectively reverses the carboxylic acid-directed anti-Markovnikov selectivity in oxidative amination of 4-pentenoic acid, successfully constructing γ-ketoamide derivatives.

Palladium-catalyzed 1,1-aminoxylation of 3-butenoic acid with 2-alkynylanilines

Herein, a palladium-catalyzed 1,1-aminoxylation of 3-butenoic acid and 2-alkynylanilines has been developed, achieving the installation of two distinct heteroatom motifs across an olefin skeleton. The strategy features a high step and atom economy and good functional group tolerance, which outlines an efficient approach for simultaneously building up γ-butylactone and indole skeletons. Notably, an external ligand, 2,9-dimethyl-1,10-phenanthroline, has been used to succeed in this protocol to effectively suppress the production of indole byproducts.

Asymmetric 1,n-Remote Aminoacetoxylation of Unactivated Internal Alkenes Enabled by Palladium Catalysis

A palladium-catalyzed asymmetric 1,n-remote aminoacetoxylation of cis-alkenes has been developed using PhI(OAc)2 as an oxidant, providing the acetoxylated lactams with excellent enantioselectivities under mild reaction conditions. The sterically hindered pyridine-oxazoline (Pyox) L3 with a tert-butyl group in oxazoline ring and propyl group in C6 position of pyridinyl is vital for the reaction, where the former is good for asymmetric aminopalladation step and the latter for the chain walking process. The enantioenriched lactam products were proven to be good building blocks for the synthesis of azabicycles.

Palladium-catalyzed cascade of aza-Wacker and Povarov reactions of aryl amines and 1,6-dienes for hexahydro-cyclopenta[b]quinoline framework

Palladium catalyzed tandem reaction represents a one-pot synthetic approach to efficiently synthesize complex functionalized molecules while reducing synthetic steps, aligning with the principles of green chemistry. However, achieving a direct cascade of the aza-Wacker and Povarov reactions in one-pot synthesis presents a challenge due to substrate compatibility issues between the two reactions. In this work, we describe an aza-Wacker/Povarov reaction employing a highly electrophilic palladium catalyst, which effectively converts anilines and 1,6-dienes into hexahydro-cyclopenta[b]quinolines. The optimized conditions yield up to 79%, with a diastereoselectivity > 20:1. Substrate range testing reveals compatibility with various sensitive functional groups, and successful late-stage modifications are performed on several natural products and drug molecules, demonstrating the versatility and practicality of the method. Additionally, a preliminary investigation into the reaction mechanism suggests an aza-Wacker process followed by a Povarov process.

Recent Progress in Synthesis of Alkyl Fluorinated Compounds with Multiple Contiguous Stereogenic Centers

Organic fluorides are widely used in pharmaceuticals, agrochemicals, material sciences, and other fields due to the special physical and chemical properties of fluorine atoms. The synthesis of alkyl fluorinated compounds bearing multiple contiguous stereogenic centers is the most challenging research area in synthetic chemistry and has received extensive attention from chemists. This review summarized the important research progress in the field over the past decade, including asymmetric electrophilic fluorination and the asymmetric elaboration of fluorinated substrates (such as allylic alkylation reactions, hydrofunctionalization reactions, Mannich addition reactions, Michael addition reactions, aldol addition reactions, and miscellaneous reactions), with an emphasis on synthetic methodologies, substrate scopes, and reaction mechanisms.

Water mediated redox-neutral cleavage of arylalkenes via photoredox catalysis

Cleavage of carbon-carbon bonds remains a challenging task in organic synthesis. Traditional methods for splitting Csp2=Csp2 bonds into two halves typically involve non-redox (metathesis) or oxidative (ozonolysis) mechanisms, limiting their synthetic potential. Disproportionative deconstruction of alkenes, which yields one reduced and one oxidized fragment, remains an unexplored area. In this study, we introduce a redox-neutral approach for deleting a Csp2 carbon unit from substituted arylalkenes, resulting in the formation of an arene (reduction) and a carbonyl product (oxidation). This transformation is believed to proceed through a mechanistic sequence involving visible-light-promoted anti-Markovnikov hydration, followed by photoredox cleavage of Csp3-Csp3 bond in the alcohol intermediate. A crucial consideration in this design is addressing the compatibility between the highly reactive oxy radical species in the latter step and the required hydrogen-atom-transfer (HAT) reagent for both steps. We found that ethyl thioglycolate serves as the optimal hydrogen-atom shuttle, offering remarkable chemoselectivity among multiple potential HAT events in this transformation. By using D2O, we successfully prepared dideuteromethylated (-CD2H) arenes with good heavy atom enrichment. This work presents a redox-neutral alternative for alkene deconstruction, with considerable potential in late-stage modification of complex molecules.

Synthetic techniques for thermodynamically disfavoured substituted six-membered rings

Six-membered rings are ubiquitous structural motifs in bioactive compounds and multifunctional materials. Notably, their thermodynamically disfavoured isomers, like disubstituted cyclohexanes featuring one substituent in an equatorial position and the other in an axial position, often exhibit enhanced physical and biological activities in comparison with their opposite isomers. However, the synthesis of thermodynamically disfavoured isomers is, by its nature, challenging, with only a limited number of possible approaches. In this Review, we summarize and compare synthetic methodologies that produce substituted six-membered rings with thermodynamically disfavoured substitution patterns. We place particular emphasis on elucidating the crucial stereoinduction factors within each transformation. Our aim is to stimulate interest in the synthesis of these unique structures, while simultaneously providing synthetic chemists with a guide to approaching this synthetic challenge.

Ligand control of regioselectivity in palladium-catalyzed heteroannulation reactions of 1,3-Dienes

Olefin carbofunctionalization reactions are indispensable tools for constructing diverse, functionalized scaffolds from simple starting materials. However, achieving precise control over regioselectivity in intermolecular reactions remains a formidable challenge. Here, we demonstrate that using PAd2nBu as a ligand enables regioselective heteroannulation of o-bromoanilines with branched 1,3-dienes through ligand control. This approach provides regiodivergent access to 3-substituted indolines, showcasing excellent regioselectivity and reactivity across a range of functionalized substrates. To gain further insights into the origin of selectivity control, we employ a data-driven strategy, developing a linear regression model using calculated parameters for phosphorus ligands. This model identifies four key parameters governing regioselectivity in this transformation, paving the way for future methodology development. Additionally, density functional theory calculations elucidate key selectivity-determining transition structures along the reaction pathway, corroborating our experimental observations and establishing a solid foundation for future advancements in regioselective olefin difunctionalization reactions.

CoH-catalyzed asymmetric remote hydroalkylation of heterocyclic alkenes: a rapid approach to chiral five-membered S- and O-heterocycles

Saturated heterocycles, which incorporate S and O heteroatoms, serve as fundamental frameworks in a diverse array of natural products, bioactive compounds, and pharmaceuticals. Herein, we describe a unique cobalt-catalyzed approach integrated with a desymmetrization strategy, facilitating precise and enantioselective remote hydroalkylation of unactivated heterocyclic alkenes. This method delivers hydroalkylation products with high yields and excellent stereoselectivity, representing good efficiency in constructing alkyl chiral centers at remote C3-positions within five-membered S/O-heterocycles. Notably, the broad scope and good functional group tolerance of this asymmetric C(sp3)-C(sp3) coupling enhance its applicability.

Palladium-Catalyzed anti-Michael-Type (Hetero)arylation of Acrylamides

This paper reports a direct α-(hetero)arylation of acrylamides through an inverse electron-demand nucleophilic addition, specifically an anti-Michael-type addition. The introduction of a quinolyl directing group facilitates the nucleophilic addition of (hetero)arenes to the α-position of acrylamides. The quinolyl directing group effectively suppresses undesired β-hydrogen elimination and is removable for subsequent derivatization. The presented method provides an atom economical synthesis of α-(hetero)arylamide with a high degree of functional group tolerance.

Observation of unusual outer-sphere mechanism using simple alkenes as nucleophiles in allylation chemistry

Transition-metal catalyzed allylic substitution reactions of alkenes are among the most efficient methods for synthesizing diene compounds, driven by the inherent preference for an inner-sphere mechanism. Here, we present a demonstration of an outer-sphere mechanism in Rh-catalyzed allylic substitution reaction of simple alkenes using gem-difluorinated cyclopropanes as allyl surrogates. This unconventional mechanism offers an opportunity for the fluorine recycling of gem-difluorinated cyclopropanes via C - F bond cleavage/reformation, ultimately delivering allylic carbofluorination products. The developed method tolerates a wide range of simple alkenes, providing access to secondary, tertiary fluorides and gem-difluorides with 100% atom economy. DFT calculations reveal that the C - C bond formation goes through an unusual outer-sphere nucleophilic substitution of the alkenes to the allyl-Rh species instead of migration insertion, and the generated carbon cation then forms the C - F bond with tetrafluoroborate as a fluoride shuttle.

Advances Toward Amphidinolides C, F and U: Isolations, Synthetic Studies and Total Syntheses

Amphidinolides C, F, and U, including C2-C4 analogs, are highly cytotoxic marine macrolides, mainly isolated from dinoflagellates of the genus Amphidinium. All these polyketides share a 75 % or more similar structure, highlighted by a macrolactone ring, at least one trans-2,5-substituted-THF motif and a characteristic polyenic side chain. From their isolation and absolute configurational assignment, the total synthesis of these marine macrolides represented an intense challenge to the organic synthesis community over the last 15 years, with around 14 research groups engaged in this inspiring task. In the first part of this review, we present the different approaches to the isolation and characterization of these natural products, including the most recent analogs, which may cast doubt on the biogenetic origin of these compounds. The various synthetic approaches to the total synthesis of C, F, and U amphidinolides are presented in a second part, focusing on key reactions and/or innovative strategies. The review concludes in a third section summarizing the successful approaches leading to the total synthesis of one of the members of this amphidinolide subfamily.

Pd(II)-Catalyzed 1,2-Oxyarylation of Alkenes with O-Acylhydroxylamines as the Oxygen Source

O-Acylhydroxylamine has been widely employed as an electrophilic amination reagent in transition-metal-catalyzed C-N coupling reactions, but its use as an electrophilic oxygen source has not been disclosed. Here, we report a Pd-catalyzed 1,2-oxyarylation of alkenes with O-acylhydroxylamines as an oxidant and an oxygen source for the first time. With simple amide as the monodentate directing group, this method features a broad substrate scope, good functional group tolerance, and mild conditions.

Mechanistic Analysis Reveals Key Role of Interchalcogen Multicatalysis in Photo-Aerobic 3-Pyrroline Syntheses by Aza-Wacker Cyclizations

A light-driven dual and ternary catalytic aza-Wacker protocol for the construction of 3-pyrrolines by partially disulfide-assisted selenium-π-acid multicatalysis is reported. A structurally diverse array of sulfonamides possessing homopolar mono-, di- and trisubstituted olefinic double bonds is selectively converted to the corresponding 3-pyrrolines in up to 95 % isolated yield and with good functional group tolerance. Advanced electrochemical mechanistic investigations of the protocol suggest a dual role of the disulfide co-catalyst. On the one hand, the disulfide serves as an electron hole shuttle between the excited photoredox catalyst and the selenium co-catalyst. On the other hand, the sulfur species engages in the final, product releasing step of the catalytic cycle by accelerating the β-elimination of the selenium moiety, which was found in many cases to lead to considerably improved product yields.

A Bimolecular Homolytic Substitution-Enabled Platform for Multicomponent Cross-Coupling of Unactivated Alkenes

The construction of C(sp3)-C(sp3) bonds remains one of the most difficult challenges in cross-coupling chemistry. Here, we report a photoredox/nickel dual catalytic approach that enables the simultaneous formation of two C(sp3)-C(sp3) linkages via trimolecular cross-coupling of alkenes with alkyl halides and hypervalent iodine-based reagents. The reaction harnesses a bimolecular homolytic substitution (SH2) mechanism and chemoselective halogen-atom transfer (XAT) to orchestrate the regioselective addition of electrophilic and nucleophilic alkyl radicals across unactivated alkenes without the need for a directing auxiliary. Utility is highlighted through late-stage (fluoro)alkylation and (trideutero)methylation of C═C bonds bearing different substitution patterns, offering straightforward access to drug-like molecules comprising sp3-hybridized carbon scaffolds.

A free-radical design featuring an intramolecular migration for a synthetically versatile alkyl-(hetero)arylation of simple olefins

A free-radical approach has enabled the development of a synthetically versatile alkyl-(hetero)arylation of olefins. Alkyl and (hetero)aryl groups were added concurrently to a full suite of mono- to tetrasubstituted simple alkenes (i.e., without requiring directing or electronically activating groups) for the first time. Key advances also included the introduction of synthetically diversifiable alkyl groups featuring different degrees of substitution, good diastereocontrol in both cyclic and acyclic settings, the addition of biologically valuable heteroarenes featuring Lewis basic nitrogen atoms as well as simple benzenes, and the generation of either tertiary or quaternary benzylic centers. The synthetic potential of this transformation was demonstrated by leveraging it as the key step in a concise synthesis of oliceridine, a new painkiller that received FDA approval in 2020.

Catalytic Enantioselective Aminative Difunctionalization of Alkenes

Enantioselective difunctionalization of alkenes offers a straightforward means for the rapid construction of enantioenriched complex molecules. Despite the tremendous efforts devoted to this field, enantioselective aminative difunctionalization remains a challenge, particularly through an electrophilic addition fashion. Herein, we report an unprecedented approach for the enantioselective aminative difunctionalization of alkenes via copper-catalyzed electrophilic addition with external azo compounds as nitrogen sources. A series of valuable cyclic hydrazine derivatives via either [3 + 2] cycloaddition or intramolecular cyclization have been achieved in high chemo-, regio-, enantio-, and diastereoselectivities. In this transformation, a wide range of functional groups, such as carboxylic acid, hydroxy, amide, sulfonamide, and aryl groups, could serve as nucleophiles. Importantly, a new cyano oxazoline chiral ligand was found to play a crucial role in the control of enantioselectivity.

Hydrogen Atom Transfer (HAT)-Mediated Remote Desaturation Enabled by Fe/Cr-H Cooperative Catalysis

An iron/chromium system (Fe(OAc)2, CpCr(CO)3H) catalyzes the preparation of β,γ- or γ,δ-unsaturated amides from 1,4,2-dioxazol-5-ones. An acyl nitrenoid iron complex seems likely to be responsible for C-H activation. A cascade of three H• transfer steps appears to be involved: (i) the abstraction of H• from a remote C-H bond by the nitrenoid N, (ii) the transfer of H• from Cr to N, and (iii) the abstraction of H• from a radical substituent by the Cr•. The observed kinetic isotope effects are consistent with the proposed mechanism if nitrenoid formation is the rate-determining step. The Fe/Cr catalysts can also desaturate substituted 1,4,2-dioxazol-5-ones to 3,5-dienamides.

Cooperative Fe/Co-Catalyzed Remote Desaturation for the Synthesis of Unsaturated Amide Derivatives

Unsaturated amides represent common functional groups found in natural products and bioactive molecules and serve as versatile synthetic building blocks. Here, we report an iron(II)/cobalt(II) dual catalytic system for the syntheses of distally unsaturated amide derivatives. The transformation proceeds through an iron nitrenoid-mediated 1,5-hydrogen atom transfer (1,5-HAT) mechanism. Subsequently, the radical intermediate undergoes hydrogen atom abstraction from vicinal methylene by a cobaloxime catalyst, efficiently yielding β,γ- or γ,δ-unsaturated amide derivatives under mild conditions. The efficiency of Co-mediated HAT can be tuned by varying different auxiliaries, highlighting the generality of this protocol. Remarkably, this desaturation protocol is also amenable to practical scalability, enabling the synthesis of unsaturated carbamates and ureas, which can be readily converted into various valuable molecules.

Nickel-Catalyzed Reductive Alkene Cross-Dialkylation with Unactivated Alkyl Electrophiles

A Ni-catalyzed reductive dialkylation of 8-aminoquinoline-tethered aliphatic alkenes with two unactivated alkyl electrophiles is disclosed here. Key to the development of this transformation is the combination of primary alkyl (pseudo)halides and secondary alkyl iodides that produce products in a single regioselective manner. The reaction exhibits good functional group compatibility, and its synthetic utility was demonstrated by the concise synthesis of the precursors of biologically relevant molecules.

Biocatalytic, Stereoconvergent Alkylation of (Z/E)-Trisubstituted Silyl Enol Ethers

Alkene functionalization has garnered significant attention due to the versatile reactivity of C=C bonds. A major challenge is the selective conversion of isomeric alkenes into chiral products. Researchers have devised various biocatalytic strategies to transform isomeric alkenes into stereopure compounds; while selective, the enzymes often specifically convert one alkene isomer, thereby diminishing overall yield. To increase the overall yield, scientists have introduced additional driving forces to interconvert alkene isomers. This improves the yield of biocatalytic alkene functionalization at the cost of increased energy consumption and chemical waste. Developing a stereoconvergent enzyme for alkene functionalization offers an ideal solution, although such catalysts are rarely reported. Here we present engineered hemoproteins derived from a bacterial cytochrome P450 that efficiently catalyze the stereoconvergent α-carbonyl alkylation of isomeric silyl enol ethers, producing stereopure products. Through screening and directed evolution, we generated P450BM3 variant SCA-G2, which catalyzes stereoconvergent carbene transfer in E. coli, with high efficiency and stereoselectivity toward various Z/E mixtures of silyl enol ethers. In contrast to established stereospecific transformations that leave one isomer unreacted, SCA-G2 converts both isomers to a stereopure product. This biocatalytic approach simplifies the synthesis of chiral α-branched ketones by eliminating the need for stoichiometric chiral auxiliaries, strongly basic alkali-metal enolates, and harsh conditions, delivering products with high efficiency and excellent chemo- and stereoselectivities.

Overcoming Radical Stability Order via DABCO-Triggered Desulfurization: Visible-Light-Promoted 1,2,4-Trifunctionalization of Butenyl Benzothiazole Sulfone with Thiosulfonate

A radical 1,2,4-trifunctional reaction of thiosulfonate to unactivated olefin is achieved by a migration strategy under mild conditions. In this reaction, the more unstable primary free radicals are in situ generated after the migration of heteroaryl groups in the presence of DABCO. This trifunctionalization of unactivated olefins involves two C-S bond formations and one C-C bond formation.

Transition-Metal-Catalyzed 1,2-Diaminations of Olefins: Synthetic Methodologies and Mechanistic Studies

1,2-Diamines are synthetically important motifs in organo-catalysis, natural products, and drug research. Continuous utilization of transition-metal based catalyst in direct 1,2-diamination of olefines, in contrast to metal-free transformations, with numerous impressive advances made in recent years (2015-2023). This review summarized contemporary research on the transition-metal catalyzed/mediated [e. g., Cu(II), Pd(II), Fe(II), Rh(III), Ir(III), and Co(II)] 1,2-diamination (asymmetric and non-asymmetric) especially emphasizing the recent synthetic methodologies and mechanistic understandings. Moreover, up-to-date discussion on (i) paramount role of oxidant and catalyst (ii) key achievements (iii) generality and uniqueness, (iv) synthetic limitations or future challenges, and (v) future opportunities are summarized related to this potential area.