Palladium(II)-Catalyzed Oxidative Difunctionalization of Alkenes: Bond Forming at a High-Valent Palladium Center

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.

Copper-Catalyzed Trifunctionalization of Heteroaryl-Substituted 1-Hexenes via Remote Heteroaryl Migration

A copper-catalyzed trifunctionalization (trifluoromethylation, heteroarylation, and cyanation) of heteroaryl-substituted 1-hexenes via remote heteroaryl migration is reported. A variety of CF3 and heteroaryl-containing nitriles were readily constructed under mild conditions. The reaction features high chemo- and regioselectivities and represents a convenient method for the synthesis of multifunctionalized molecules in organic synthesis.

Dual Photoredox/Copper-Catalyzed Three-Component Alkylcyanation of Alkenes and 1,4-Alkylcyanation of 1,3-Enynes Employing Sulfoxonium Ylides as the Carbon Radical Precursors

A novel dual photoredox/copper-catalyzed three-component alkylcyanation of alkenes and 1,4-alkylcyanation of 1,3-enynes have been developed. In this radical cyanoalkylation reaction, the photoredox induced alkyl radical from sulfoxonium ylides adds to the carbon-carbon double bonds of styrenes or 1,3-enynes, and the generated benzylic or allenyl radicals couple with a Cu(II) cyanide complex to achieve selective cyanation. The reaction exhibits high chemo- and regioselectivity and a wide substrate scope, providing an efficient method for the synthesis of alkyl nitriles and allenyl nitriles in a single step.

Palladium-catalyzed remote internal C(sp3)-H bond chlorination of alkenes

C(sp3)-Cl bonds are present in numerous biologically active molecules and can also be used as a site for diversification by substitution or cross-coupling reactions. Herein, we report a remote internal site-selective C(sp3)-H bond chlorination of alkenes through sequential alkene isomerization and hydrochlorination, enabling the synthesis of both benzylic and tertiary chlorides with excellent site-selectivity. This transformation offers exciting possibilities for the late-stage chlorination of derivatives of natural products and pharmaceuticals. We also demonstrate the regioconvergent synthesis of a single alkyl chloride from unrefined mixtures of isomeric alkenes, which can be extracted directly from petrochemical sources.

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.

Direct alkene functionalization via photocatalytic hydrogen atom transfer from C(sp3)-H compounds: a route to pharmaceutically important molecules

Direct functionalization of alkenes with C(sp3)-H substrates offers unique opportunities for the rapid construction of pharmaceuticals and natural products. Although significant progress has been made over the past decades, the development of green, high step-economy methods to achieve these transformations under mild conditions without the need for pre-functionalization of C(sp3)-H bonds remains a substantial challenge. Therefore, the pursuit of such methodologies is highly desirable. Recently, the direct activation of C(sp3)-H bonds via photocatalytic hydrogen atom transfer (HAT), especially from unactivated alkanes, has shown great promise. Given the potential of this approach to generate a wide range of pharmaceutically relevant compounds, this review highlights the recent advancements in the direct functionalization of alkenes through photocatalytic HAT from C(sp3)-H compounds, as well as their applications in the synthesis and diversification of drugs, natural products, and bioactive molecules, aiming to provide medicinal chemists with a practical set of tools.

Enantioselective Intramolecular Oxidative Aminoacetoxylation from Aryl-Substituted Alkene via Chiral Triazole-oxazoline Palladium Complexes

Here, we describe an enantioselective intramolecular oxidative aminoacetoxylation reaction using a palladium catalyst and an aryl-substituted internal alkene compound as the substrate under mild conditions in several hours. The triazole-oxazoline ligand was selected for the asymmetric catalyst. A range of enantioenriched pyrrolidine-derived vicinal amino acetate compounds were synthesized, showing yields from 47% to 84%, diastereomer ratios from 57:43 to 95:5, and enantiomer excesses from 67% to 92%.

Multifunctionalization of Alkenyl Alcohols via a Sequential Relay Process

Aryl-substituted aliphatic amines are widely recognized as immensely valuable molecules. Consequently, the development of practical strategies for the construction of these molecules becomes increasingly urgent and critical. Here, we have successfully achieved multifunctionalization reactions of alkenyl alcohols in a sequential relay process, which enables transformation patterns of arylamination, deuterated arylamination, and methylenated arylamination to the easy access of multifarious arylalkylamines. Notably, a novel functionalization mode for carbonyl groups has been developed to facilitate the processes of deuterium incorporation and methylene introduction, thereby providing new means for the diverse transformations of carbonyl groups. This methodology displays a wide tolerance toward functional groups, while also exhibiting good applicability across various skeletal structures of alkenols and amines.

Photo-/Electrocatalytic Difunctionalization of Alkenes Enabled by C-H Radical Functionalization

The difunctionalization of alkenes represents a powerful tool to incorporate two functional groups into the alkene bones for increasing molecular complexity and has been widely utilizations in chemical synthesis. Upon the catalysis of the green, sustainable, mild photo-/electrochemistry technologies, much attentions have been attracted to the development of new tactics for the transformations of the important alkene and alkane feedstocks driven by C-H radical functionalization. Herein, we summarize recent advances in the photo-/electrocatalytic difunctionalization of alkenes enabled by C-H radical functionalization. We detailedly discuss the substrate scope and the mechanisms of the photo-/electrocatalytic alkene difunctionalization reactions by selecting impressive synthetic examples, which are divided into four sections based on the final terminated step, including oxidative radical-polar crossover coupling, reductive radical-polar crossover coupling, radical-radical coupling, and transition-metal-catalyzed coupling.

Chemoselective Pd-Based Dyotropic Rearrangement: Fluorocyclization and Regioselective Wacker Reaction of Homoallylic Amides

Fluorocyclization of alkenes tethered with a pronucleophile is an efficient transformation that converts easily accessible starting materials to fluorinated heterocycles in a single step. We report herein an unprecedented Pd(II)-catalyzed oxidative domino process that transforms homoallylic amides to 5,6-dihydro-4H-1,3-oxazines through a domino oxypalladation/PdII-oxidation/dyotropic rearrangement/reductive elimination sequence. Three chemical bonds are created under these operationally simple conditions. Taking advantage of the facile hydrolysis of the α-fluoro tertiary alkyl ether under acidic conditions, a one-pot conversion of homoallylic amides to homologated ketones is subsequently developed, which represents a rare example of regioselective Wacker oxidation reaction of 1,1-disubstituted alkenes.

Cu0-Promoted Truce-Smiles Rearrangement for Aryl-Difluoromethylenation of C═C Bonds via a Reductive Radical-Polar Crossover Process

An efficient Cu0-promoted Truce-Smiles rearrangement for the aryl-difluoromethylenation of C═C bonds by the reaction of N-alkyl-N-(arylsulfonyl)methacrylamide and 2-bromodifluoromethyl-1,3-benzodiazole via a reductive radical-polar crossover process under mild reaction conditions is presented. The protocol enables practical access to a variety of single regioisomer α-aryl-β-difluoromethylene amides in good to excellent yields through consecutive difluoromethylenation, radical-polar crossover, 1,4-aryl migration, SO2 extrusion, and N-H bond formation cascade reaction.

Remote Functionalization of Inert C(sp3)-H Bonds via Dual Catalysis Driven by Alkene Hydrofluoroalkylation Using Industrial Feedstocks

We have developed a dual-catalytic system capable of site-selective azidation of inert C(sp3)-H bonds with concomitant and modular anti-Markovnikov alkene fluoroalkylation. The protocol leverages the synergetic cooperation of both the photocatalyst and earth-abundant iron catalyst to deliver two radical species in succession to minimally functionalized alkenes. This powerful catalyst system exhibits broad scope, mild conditions, and excellent regioselectivity for a variety of substrates and fluoroalkyl fragments. The key to this C-centered radical relay is the matched rate of both photocatalytic and iron catalytic cycles, ensuring selective azidofluoroalkylation with a broad array of fluoroalkyl sources from trivial reagents.

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.

Palladium and copper co-catalyzed chloro-arylation of gem-difluorostyrenes - use of a nitrite additive to suppress β-F elimination

The installation of fluorine and fluorinated functional groups in organic molecules perturbs the physicochemical properties of those molecules and enables the development of new therapeutics, agrichemicals, biological probes and materials. However, current synthetic methodologies cannot access some fluorinated functional groups and fluorinated scaffolds. One such group, the gem-difluorobenzyl motif, might be convergently synthesized by reacting a nucleophilic aryl precursor and an electrophilic gem-difluoroalkene. Previous attempts have relied on forming unstable anionic or organometallic intermediates that rapidly decompose through a β-F elimination process to deliver monofluorovinyl products. In contrast, we report a fluorine-retentive palladium and copper co-catalyzed chloro-arylation of gem-difluorostyrenes that takes advantage of a nitrite (NO2 -) additive to avoid the favorable β-F elimination pathway that forms monofluorinated products, instead delivering difluorinated products.

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.

Defluorinative Haloalkylation of Unactivated Alkenes Enabled by Dual Photoredox and Copper Catalysis

A three-component defluorinative haloalkylation of alkenes with trifluoromethyl compounds and TBAX (X = Cl, Br) via dual photoredox/copper catalysis is reported. The mild conditions are compatible with a wide array of activated trifluoromethyl aromatics bearing diverse substituents, and various nonactivated terminal and internal alkenes, enabling straightforward access to synthetically valuable γ-gem-difluoroalkyl halides with high efficiency. Mechanistic studies indicate that the [Cu] complexes not only serve as XAT catalysts but also facilitate the SET reduction of trifluoromethyl groups by photocatalysts. Additionally, the resulting alkyl halide products can serve as versatile conversion intermediates for the synthesis of a diverse range of γ-gem-difluoroalkyl compounds.

Arylcyanation of Styrenes by Photoactive Electron Donor-Acceptor Complexes/Copper Catalysis

A novel electron donor-acceptor (EDA) complex/copper catalysis model has been proposed for the construction of 2,3-diarylpropionitriles under visible light conditions. The developed protocol proceeds via intermolecular charge transfer between the photoactive EDA complex of dibutamine (DBA), aryl thianthrenium salts, and trimethylsilyl cyanide (TMSCN), followed by a copper catalytic cycle. UV-vis absorption measurements confirm the participation of EDA complexes as reactive intermediates. This three-component process proceeds smoothly in the presence of pharmaceutically relevant core structures and sensitive functional groups, which offers the possibility of the precise editing of drug molecules with important scaffolds.

Visible-light-induced redox-neutral difunctionalization of alkenes and alkynes

The twelve principles of green chemistry illuminate the pathway in the direction of sustainable and eco-friendly synthesis, marking a fundamental shift in synthetic organic chemistry paradigms. In this realm, harnessing the power of visible light for the difunctionalization of various skeletons without employing any external oxidant or reductant, specifically termed as redox-neutral difunctionalization, has attracted tremendous interest from synthetic organic chemists due to its low cost, easy availability and environmentally friendly nature in contrast to traditional metal-catalyzed difunctionalizations. This review presents an overview of recent updates on visible-light-induced redox-neutral difunctionalization reactions with literature coverage up to May 2024.

Recent Advances in Direct Regioselective C-H Chlorination at Aromatic and Aliphatic

Direct installation of key functionalities in a molecule through C-H bond activation is one of the thrust areas as well as challenging task in organic synthesis. Particularly, introduction of chlorine in a molecule imparts additional benefits for further functionalizations as well as improves the electronic behaviour such as lipophilicity and polarity towards drug development process. The chlorinated molecules have also been established as efficient biologically relevant scaffolds. Current manuscript has been focused on the direct installation of the chlorine atom at various aromatic and aliphatic positions to produce functional molecules. The key highlight of the manuscript belongs to the site selectivity (regioselectivity) for the installation of chlorine functionality. Manuscript describes the advanced methods developed for the direct C-H chlorination reactions and further simplified for the chlorination reactions at various positions including aromatic (o-, m-, and p-), benzylic, heteroaromatic, and aliphatic positions. Directing groups (DGs) and the coordination with the catalyst is the key for the enhancement of regioselectivities during direct C-H chlorination reactions.

C-H functionalization reactions catalyzed by artificial metalloenzymes

CH functionalization, a promising frontier in modern organic chemistry, facilitates the direct conversion of inert CH bonds into many valuable functional groups. Despite its merits, traditional homogeneous catalysis, often faces challenges in efficiency, selectivity, and sustainability towards this transformation. In this context, artificial metalloenzymes (ArMs), resulting from the incorporation of a catalytically-competent metal cofactor within an evolvable protein scaffold, bridges the gap between the efficiency of enzymatic transformations and the versatility of transition metal catalysis. Accordingly, ArMs have emerged as attractive tools for various challenging catalytic transformations. Additionally, the coming of age of directed evolution has unlocked unprecedented avenues for optimizing enzymatic catalysis. Taking advantage of their genetically-encoded protein scaffold, ArMs have been evolved to catalyze various CH functionalization reactions. This review delves into the recent developments of ArM-catalyzed CH functionalization reactions, highlighting the benefits of engineering the second coordination sphere around a metal cofactor within a host protein.

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.

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.

Expedient, regioselective C-H chalcogenation of 3,4-dihydro-1,4-benzoxazines using a palladium-copper catalyst

The palladium-catalysed regioselective C-H chalcogenation of benzoxazines with disulfides and diselenides in air has been described. In this protocol, palladium acetate serves as the catalyst in conjunction with copper as an oxidizing agent. Through this approach, a wide array of sulfenylation and selenylation reactions of benzomorpholines have been effected, yielding results ranging from good to excellent. Thus, the established procedure demonstrates superb regioselectivity and a strong tolerance towards various functional groups and is suitable for gram-scale synthesis. Additionally, this synthetic approach offers a practical and convenient pathway for late-stage functionalization leading to the Rosenmund-von Braun reaction.

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.

Transition metal-free decarboxylative olefination of carboxylic acid salts

The cost-effective and efficient synthesis of alkenes is highly significant due to their extensive applications in both synthetic and polymer industries. A transition metal-free approach has been devised for the chemoselective olefination of carboxylic acid salts. This modular approach provides direct access to valuable electron-deficient styrenes in moderate to good yields. Detailed mechanistic studies suggest anionic decarboxylation is followed by halogen ion transfer. This halogen transfer leads to an umpolung of reactant electronics, allowing for a rate-limiting rebound elimination.

Synthesis of Sterically Hindered Dialkyl Ethers via Palladium-Catalyzed Fluoro-alkoxylation of gem-Difluoroalkenes

Organofluorine compounds are of high value in medicinal and agricultural chemistry. Herein, we report a palladium-catalyzed fluoro-alkoxylation of gem-difluoroalkenes for the synthesis of much more challenging sterically hindered ethers. This reaction represents a direct synthesis method for α-trifluoromethyl ethers with a broad functional group tolerance and excellent regioselectivity. This system employs N-fluorobenzenesulfonimide (NFSI) as an electrophilic fluorine source and alcohols as nucleophilic donors, including but not limited to sterically hindered tert-substituted alcohols.

Electrochemical Oxidative Sulfonylation-Azidation of Alkenes

A novel electrochemical oxidative sulfonylation-azidation of alkenes is accomplished by using sulfonyl hydrazide and trimethylsilyl azide (TMSN3) for the one-pot and green synthesis of β-azidoarylsulfone, which involves the direct construction of new C-S and C-N bonds. Notably, neither exogenous oxidants/additives nor metal catalysts are required for this method. In addition, this electrochemical strategy features mild conditions and wide substrate scope and has been proved to be a radical pathway by mechanistic studies.

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.

Recent Advances in Palladium-Catalyzed Asymmetric Heck/Tsuji-Trost Reactions of 1,n-Dienes

Transition-metal catalyzed tandem asymmetric reactions were powerful tools to access various chiral compounds. Many strategies have been developed for the coupling of 1,n-dienes with aryl halides via a tandem Heck/Tsuji-Trost process. However, the control of regio- and stereo-chemistry remains a challenging task. This minireview details the recent advances in the field of asymmetric Heck/Tsuji-Trost reactions catalyzed by palladium complex, which have opened new opportunities and expanded our understanding in this area of research in recent years.

Photochemical Mn-Mediated Generation of Azide Radicals for Improvement of Alkene Hydroxyazidation

State-of-the-art strategies for alkene-hydroxyazidation, which yield a mixture of β-azido alcohol and β-azido peroxide, must rely on phosphine reagents to improve the chemoselectivity. To overcome the above problems, we present a photochemical hydroxyazidation of alkenes via Mn-mediated ligand-to-metal charge transfer (LMCT) in O2, which activates N3- to •N3 and incorporates O2 to be used as an oxygen source in the hydroxyazidation products. Broad alkene range and step-economy chemistry for the hydroxyazidation transformation were also demonstrated.

Palladium-Catalyzed Carbohalogenation of Olefins with Alkynyl Oxime Ethers: Rapid Access to Chlorine-Containing Isoxazoles

A palladium-catalyzed carbohalogenation of olefins with alkynyl oxime ethers has been described, which provides efficient and practical access to various chlorine-containing isoxazoles. This method exhibits excellent regioselectivity, good functional group compatibility, and mild reaction conditions. The mechanistic studies suggest that the reaction proceeds via a stabilized π-benzyl palladium intermediate, which is essential for the formation of C(sp3)-Cl bonds.

Catalytic 1,1-diazidation of alkenes

Compared to well-developed catalytic 1,2-diazidation of alkenes to produce vicinal diazides, the corresponding catalytic 1,1-diazidation of alkenes to yield geminal diazides has not been realized. Here we report an efficient approach for catalytic 1,1-diazidation of alkenes by redox-active selenium catalysis. Under mild conditions, electron-rich aryl alkenes with Z or E or Z/E mixed configuration can undergo migratory 1,1-diazidation to give a series of functionalized monoalkyl or dialkyl geminal diazides that are difficult to access by other methods. The method is also effective for the construction of polydiazides. The formed diazides are relatively safe by TGA-DSC analysis and impact sensitivity tests, and can be easily converted into various valuable molecules. In addition, interesting reactivity that geminal diazides give valuable molecules via the geminal diazidomethyl moiety as a formal leaving group in the presence of Lewis acid is disclosed. Mechanistic studies revealed that a selenenylation-deselenenylation followed by 1,2-aryl migration process is involved in the reactions, which provides a basis for the design of new reactions.

Phenyliodine bis(trifluoroacetate) as a sustainable reagent: exploring its significance in organic synthesis

Iodine-containing molecules, especially hypervalent iodine compounds, have gained significant attention in organic synthesis. They are valuable and sustainable reagents, leading to a remarkable surge in their use for chemical transformations. One such hypervalent iodine compound, phenyliodine bis(trifluoroacetate)/bis(trifluoroacetoxy)iodobenzene, commonly referred to as PIFA, has emerged as a prominent candidate due to its attributes of facile manipulation, moderate reactivity, low toxicity, and ready availability. PIFA presents an auspicious prospect as a substitute for costly organometallic catalysts and environmentally hazardous oxidants containing heavy metals. PIFA exhibits remarkable catalytic activity, facilitating an array of consequential organic reactions, including sulfenylation, alkylarylation, oxidative coupling, cascade reactions, amination, amidation, ring-rearrangement, carboxylation, and numerous others. Over the past decade, the application of PIFA in synthetic chemistry has witnessed substantial growth, necessitating an updated exploration of this field. In this discourse, we present a concise overview of PIFA's applications as a 'green' reagent in the domain of synthetic organic chemistry. A primary objective of this article is to bring to the forefront the scientific community's awareness of the merits associated with adopting PIFA as an environmentally conscientious alternative to heavy metals.

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.

Synthesis of aminoalcohols from substituted alkenes via tungstenooxaziridine catalysis

Herein we report the WO2Dipic(H2O) promoted oxyamination of alkenes using sulfonamides as the quantitative source of N. The reaction works for activated and unactivated alkenes in high yields, diastereoselectivities, and stereospecificity. A catalytic cycle involving the formation of tungstenooxaziridine complex 1 as the active catalyst and hydrolysis of tungstenooxazolidine intermediate A as the rate-determining-step has been proposed. Initial kinetic and competition experiments provide evidence for the proposed mechanism.

Arylthianthrenium Salts as the Aryl Sources: Visible Light/Copper Catalysis-Enabled Intermolecular Azidosulfonylation of Alkenes

The difunctionalization of alkenes using aryl thianthrenium salts as the aryl sources has been reported sporadically. However, the four-component difunctionalization of alkenes on the basis of aryl thianthrenium salts has not been reported thus far and still remains a challenge. Herein, a visible light/copper catalysis-enabled four-component reaction of aryl thianthrenium salts, DABCO·(SO2)2, alkenes, and TMSN3 is presented, which affords a facile approach to β-azidosulfones in good yields with broad substrate scope and excellent functional group tolerance. This strategy indirectly realizes the method for the synthesis of β-azidosulfones through site-selective aryl C-H bond functionalization and alkene difunctionalization. This developed method is an important complement to thianthrenium salts chemistry.

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.

Electrochemical Azidocyanation of Alkenes

The difunctionalization of alkenes-a process that installs two functional groups in a single operation and transforms chemical feedstocks into value-added products-is one of the most appealing synthetic methods in contemporary chemistry. However, the introduction of two distinct functional groups via two readily accessible nucleophiles remains a formidable challenge. Existing intermolecular alkene azidocyanation methods, which primarily focus on aryl alkenes and rely on stoichiometric chemical oxidants. We report herein an unprecedented electrochemical strategy for alkene azidocyanation that is compatible with both alkyl and aryl alkenes. This is achieved by harnessing the finely-tuned anodic electron transfer and the strategic selection of copper/ligand complexes. The reactions of aryl alkenes were rendered enantioselective by employing a chiral ligand. Crucially, the mild conditions and well-regulated electrochemical process assure exceptional tolerance for various functional groups and substrate compatibility with both terminal and internal alkyl alkenes.

A four-component reaction to access 3,3-disubstituted indolines via the palladium-norbornene-catalyzed ortho amination/ipso conjunctive coupling

As an important class of multicomponent reactions, the palladium/norbornene (Pd/NBE) cooperative catalysis has been mainly restricted to the coupling of an aryl halide, an electrophile and a nucleophile. Here, we report the development of a Pd/NBE-catalyzed four-component reaction, which involves ortho C-H amination/ipso conjunctive coupling using an alkene and an external nucleophile. The use of alkene-tethered nitrogen electrophiles provides a rapid and modular synthesis of 3,3-disubstituted indolines from readily available aryl iodides. The reaction exhibits broad functional group tolerance, and its utility is exemplified in a streamlined formal synthesis of a rhodamine dye. Preliminary results of the asymmetric version of this reaction have also been obtained.

Metal-free synthesis of 1,3-dichloro-1,5-diarylpentan-5-ones via cascade oxidative radical addition of styrenes with CHCl3

A novel and efficient metal-free cascade oxidative radical addition of styrenes is developed for the construction of 1,3-dichloro-1,5-diarylpentan-5-ones. This protocol presents a practical one-pot procedure that delivers highly functionalized 1,3-dichloro-1,5-diarylpentan-5-ones in moderate-to-good yields with a broad substrate scope under mild conditions.

Iodonium based regioselective double nucleophilic alkene functionalization of a hydrofluoroolefin scaffold

Herein, we report a modular regioselective alkene difunctionalization strategy based on the use of hydrofluoroolefin (HFO) gas as fluorous feedstock material. The transformation of the HFO gas to iodonium salt creates vicinal electrophilic sites readily available for a broad range of nucleophiles.

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.

Synthesis of β-Hydroxysulfides via Multi-Component Cascade Hydroxysulfenylation of Styrenes with NH4 SCN and Water under Transition-metal-free Conditions

Transition-mental-free multi-component hydroxysulfenylation of styrenes with NH4 SCN and water to from β-hydroxysulfides is established. The reaction mechanism proceeded via a domino reaction after a radical addition to 2-phenylimidazo[1,2-a]pyridines. This approach features a wide substrate scope and functional group compatibility, providing 34 compounds in acceptable yields.

Photocatalytic, modular difunctionalization of alkenes enabled by ligand-to-metal charge transfer and radical ligand transfer

Ligand-to-metal charge transfer (LMCT) is a mechanistic strategy that provides a powerful tool to access diverse open-shell species using earth abundant elements and has seen tremendous growth in recent years. However, among many reaction manifolds driven by LMCT reactivity, a general and catalytic protocol for modular difunctionalization of alkenes remains unknown. Leveraging the synergistic cooperation of iron-catalyzed ligand-to-metal charge transfer and radical ligand transfer (RLT), here we report a photocatalytic, modular difunctionalization of alkenes using inexpensive iron salts catalytically to function as both radical initiator and terminator. Additionally, strategic use of a fluorine atom transfer reagent allows for general fluorochlorination of alkenes, providing the first example of interhalogen compound formation using earth abundant element photocatalysis. Broad scope, mild conditions and versatility in converting orthogonal nucleophiles (TMSN3 and NaCl) directly into corresponding open-shell radical species are demonstrated in this study, providing a robust means towards accessing vicinal diazides and homo-/hetero-dihalides motifs catalytically. These functionalities are important precursors/intermediates in medicinal and material chemistry. Preliminary mechanistic studies support the radical nature of these transformations, disclosing the tandem LMCT/RLT as a powerful reaction manifold in catalytic olefin difunctionalization.

Intermolecular Carbophosphination of Alkynes with Phosphole Oxides via Ni-Al Bimetal-Catalyzed C-P Bond Activation

Intermolecular carbophosphination reaction of alkynes or alkenes with unreactive C-P bonds remains an elusive challenge. Herein, we used a Ni-Al bimetallic catalyst to realize an intermolecular carbophosphination reaction of alkynes with 5-membered phosphole oxides, providing a series of 7-membered phosphepines in up to 94 % yield.

Few-Atomic Zero-Valent Palladium Ensembles for Efficient Reductive Dehydrogenation and Dehalogenation Catalysis

Single-atom catalysts (SACs) offer immense potential in heterogeneous catalysis due to their maximized atomic utilization and high selectivity but suffer the problem of low reactivity in catalytic reductive reactions due to their high-valent state. Here, we demonstrate that supported palladium (Pd) ensembles consisting of a few zero-valent Pd atoms (Pd1+c-red/CN) exhibit exceptional reactivity in formic acid (FA) dehydrogenation and 4-chlorophenol (4-CP) dechlorination. The initial FA dehydrogenation and 4-CP dechlorination rates of Pd1+c-red/CN are 42-104 and 16-210 times higher than that of supported Pd SACs (Pd1-ox/CN), respectively. Experimental results and density functional theory (DFT) calculations reveal that optimal adsorption sites of Pd1+c-red/CN stimulate the formation of H*, which is indispensable for 4-CP dechlorination. Moreover, direct electron transfer from Pd atoms to FA with a high electron density on Pd1+c-red/CN also contributes to the rapid 4-CP dechlorination. The superior dehalogenation capability of Pd1+c-red/CN for organohalides of great environmental and health concerns suggested its immense application potential in environmental remediation. This work highlights the pivotal roles of the structure and valence state of Pd ensembles in catalytic reductive reactions and provides a strategy to broaden the application of Pd-based catalysts for dehydrogenation and dehalogenation.