Allylic C-H amination cross-coupling furnishes tertiary amines by electrophilic metal catalysis

Palladium-catalyzed cross-coupling of alcohols with olefins by positional tuning of a counteranion

Transition metal-catalyzed cross-couplings have great potential to furnish complex ethers; however, challenges in the C(sp3)-O functionalization step have precluded general methods. Here, we describe computationally guided transition metal-ligand design that positions a hydrogen-bond acceptor anion at the reactive site to promote functionalization. A general cross-coupling of primary, secondary, and tertiary aliphatic alcohols with terminal olefins to furnish >130 ethers is achieved. The mild conditions tolerate functionality that is prone to substitution, elimination, and epimerization and achieve site selectivity in polyol settings. Mechanistic studies support the hypothesis that the ligand's geometry and electronics direct positioning of the phosphate anion at the π-allyl-palladium terminus, facilitating the phosphate's hydrogen-bond acceptor role toward the alcohol. Ligand-directed counteranion positioning in cationic transition metal catalysis has the potential to be a general strategy for promoting challenging bimolecular reactivity.

Stereodivergent access to non-natural α-amino acids via enantio- and Z/E-selective catalysis

The precise control of Z and E configurations of the carbon-carbon double bond in alkene synthesis has long been a fundamental challenge in synthetic chemistry, even more pronounced when simultaneously striving to achieve enantioselectivity [(Z,R), (Z,S), (E,R), (E,S)]. Moreover, enantiopure non-natural α-amino acids are highly sought after in organic and medicinal chemistry. In this study, we report a ligand-controlled stereodivergent synthesis of non-natural α-quaternary amino acids bearing trisubstituted alkene moieties in high yields with excellent enantioselectivity and Z/E selectivities. This success is achieved through a palladium/copper-cocatalyzed three-component assembly of readily available aryl iodides, allenes, and aldimine esters by simply tuning the chiral ligands of the palladium and copper catalysts.

Site-Selective Carbonylative Cyclization with Two Allylic C-H Bonds Enabled by Radical Differentiation

Controlling the site-selectivity of C-H functionalization is of significant importance and a formidable undertaking in synthetic organic chemistry, motivating the continuing development of efficient and sustainable technologies for activating C-H bonds. However, methods that control the site-selectivity for double C-H functionalization are rare. We herein report a conceptually new method to achieve highly site-selective C-H functionalization by implementing a radical single-out strategy. Leveraging the steric hindrance-sensitive CO-insertion as the radical differentiation process, a site-selective and stereoselective carbonylative formal [2 + 2] cycloaddition of imines and alkenes by sequential double allylic C-H bond activation was established without special and complicated HAT-reagents. This reaction was compatible with a wide range of alkenes and imines with diverse skeletons to deliver allylic β-lactams that are of synthetic and medicinal interest.

Electrochemical Allylic C(sp3)-H Isothiocyanation via [3,3]-Sigmatropic Rearrangement

The direct allylic C(sp3)-H functionalization provides a straightforward protocol for the synthesis of valuable molecules. We report herein the first chemo- and site-selective method for allylic C(sp3)-H isothiocyanation of various internal alkenes under mild electrochemical conditions. This method exhibits broad functional group tolerance and excellent selectivity and can be applied for late-stage isothiocyanation of bioactive molecules. Combined experimental and computational studies indicate that the reaction proceeds via an unexpected [3,3]-sigmatropic rearrangement.

Alkene Thianthrenation Unlocks Diverse Cation Synthons: Recent Progress and New Opportunities

Oxidative alkene functionalization reactions are a fundamental class of complexity-building organic transformations. However, the majority of established approaches rely on electrophilic reagents that limit the diversity of groups that can be installed. Recent advances have established a new approach that instead relies on the transformation of alkenes into thianthrene-derived cationic electrophiles. These linchpin intermediates can be generated selectively and undergo a diverse array of mechanistically distinct reactions with abundant nucleophiles. Taken together, this unlocks a suite of net oxidative alkene transformations that have been elusive using conventional strategies. This Minireview describes these advances and is organized around the three distinct synthons formally accessible from alkenes via thianthrenation: 1) alkenyl cations; 2) vicinal dications; 3) allyl cations. Throughout the Minireview, we illustrate how thianthrenium salts address key limitations endemic to classic alkene-derived electrophiles and highlight the mechanistic origins of these distinctions wherever possible.

Ruthenium-Catalyzed C-H Arylation of Aromatic Acids with ortho-Haloaniline To Access Phenanthridinones

Phenanthridinone is a significant moiety in pharmaceutical and material science; thus, it is highly desirable to develop an efficient and robust method to construct phenanthridinone from readily available starting materials. Herein, we report a Ru-catalyzed C-H arylation of aromatic carboxylic acids with ortho-haloanilines, followed by intramolecular dehydration to afford phenanthridinones in high yields.

Direct synthesis of branched amines enabled by dual-catalyzed allylic C─H amination of alkenes with amines

Direct conversion of hydrocarbons into amines represents an important and atom-economic goal in chemistry for decades. However, intermolecular cross-coupling of terminal alkenes with amines to form branched amines remains extremely challenging. Here, a visible-light and Co-dual catalyzed direct allylic C─H amination of alkenes with free amines to afford branched amines has been developed. Notably, challenging aliphatic amines with strong coordinating effect can be directly used as C─N coupling partner to couple with allylic C─H bond to form advanced amines with molecular complexity. Moreover, the reaction proceeds with exclusive regio- and chemoselectivity at more steric hinder position to deliver primary, secondary, and tertiary aliphatic amines with diverse substitution patterns that are difficult to access otherwise.

1,4-Aminoarylation of Butadienes via Photoinduced Palladium Catalysis

A visible-light-induced, three-component palladium-catalyzed 1,4-aminoarylation of butadienes with readily available aryl halides and aliphatic amines has been developed, affording allylamines with excellent E-selectivity. The reaction exhibits exceptional control over chemo-, regio-, and stereoselectivity, a broad substrate scope, and high functional group compatibility, as demonstrated by the late-stage functionalization of bioactive molecules. Mechanistic investigations are consistent with a photoinduced radical Pd(0)-Pd(I)-Pd(II)-Pd(0) Heck-Tsuji-Trost allylation cascade.

Cobalt-Catalyzed Carbon-Heteroatom Transfer Enables Regioselective Tricomponent 1,4-Carboamination

Tricomponent cobalt(salen)-catalyzed carbofunctionalization of unsaturated substrates by radical-polar crossover has the potential to streamline access to broad classes of heteroatom-functionalized synthetic targets, yet the reaction platform has remained elusive, despite the well-developed analogous hydrofunctionalizations mediated by high-valent alkylcobalt intermediates. We report herein the development of a cobalt(salen) catalytic system that enables carbofunctionalization. The reaction entails a tricomponent decarboxylative 1,4-carboamination of dienes and provides a direct route to aromatic allylic amines by obviating preformed allylation reagents and protection of oxidation-sensitive aromatic amines. The catalytic system merges acridine photocatalysis with cobalt(salen)-catalyzed regioselective 1,4-carbofunctionalization that facilitates the crossover of the radical and polar phases of the tricomponent coupling process, revealing critical roles of the reactants, as well as ligand effects and the nature of the formal high-valent alkylcobalt species on the chemo- and regioselectivity.

Recent Advances in Visible Light Induced Palladium Catalysis

Visible light-induced Pd catalysis has emerged as a promising subfield of photocatalysis. The hybrid nature of Pd radical species has enabled a wide array of radical-based transformations otherwise challenging or unknown via conventional Pd chemistry. In parallel to the ongoing pursuit of alternative, readily available radical precursors, notable discoveries have demonstrated that photoexcitation can alter not only oxidative addition but also other elementary steps. This Minireview highlights the recent progress in this area.

Cooperative Cu/azodiformate system-catalyzed allylic C-H amination of unactivated internal alkenes directed by aminoquinoline

Aliphatic allylic amines are common in natural products and pharmaceuticals. The oxidative intermolecular amination of C(sp3)-H bonds represents one of the most straightforward strategies to construct these motifs. However, the utilization of widely internal alkenes with amines in this transformation remains a synthetic challenge due to the inefficient coordination of metals to internal alkenes and excessive coordination with aliphatic and aromatic amines, resulting in decreasing the reactivity of the catalyst. Here, we present a regioselective Cu-catalyzed oxidative allylic C(sp3)-H amination of internal olefins with azodiformates to these problems. A removable bidentate directing group is used to control the regiochemistry and stabilize the π-allyl-metal intermediate. Noteworthy is the dual role of azodiformates as both a nitrogen source and an electrophilic oxidant for the allylic C-H activation. This protocol features simple conditions, remarkable scope and functional group tolerance as evidenced by >40 examples and exhibits high regioselectivity and excellent E/Z selectivity.

Photoredox-Catalyzed Generation of Tertiary Anions from Primary Amines via a Radical Polar Crossover

A method for the generation of tertiary carbanions via a deaminative radical-polar crossover is reported using redox active imines from α-tertiary primary amines. A variety of benzylic amines and amino esters can be used in this approach, with the latter engaging in a novel "aza-Reformatsky" reaction. Electronic trends correlate the stability of the resulting carbanion with reaction efficiency. The anions can be trapped with different electrophiles including aldehydes, ketones, imines, Michael acceptors, and H2 O/D2 O. Selective anion formation can be achieved in the presence of another equivalent or more acidic C-H bond in both an inter- and intramolecular fashion. Mechanistic studies suggest the intermediacy of a discrete carbanion intermediate.

Iridium-catalysed reductive allylic amination of α,β-unsaturated aldehydes

Allylic amination is a powerful tool for constructing N-allylic amines widely found in bioactive molecules. Generally, allylic alcohols and unsaturated hydrocarbons have been considered for allylic amination reactions to minimize waste production. Herein, we present an iridium-catalysed method for reductive allylic amination of α,β-unsaturated aldehydes with amines to afford N-allylic amines under air conditions. This protocol is demonstrated to provide products from many substrates (41 examples) in moderate-to-excellent yields. This synthetic methodology is also highlighted by the synthesis of drug molecules, optically pure products, as well as scale-up experiments.

Electrocatalytic Systems for NOx Valorization in Organonitrogen Synthesis

Inorganic nitrogen oxide (NOx ) species, such as NO, NO2 , NO3 - , NO2 - generated from the decomposition of organic matters, volcanic eruptions and lightning activated nitrogen, play important roles in the nitrogen cycle system and exploring the origin of life. Meanwhile, excessive emission of NOx gases and residues from industry and transportation causes troubling problems to the environment and human health. How to efficiently handle these wastes is a global problem. In response to the growing demand for sustainability, scientists are actively pursuing sustainable electrochemical technologies powered by renewable energy sources and efficient utilization of hydrogen energy to convert NOx species into high-value organonitrogen chemicals. In this minireview, recent advances of electrocatalytic systems for NOx species valorization in organonitrogen synthesis are classified and described, such as amino acids, amide, urea, oximes, nitrile etc., that have been widely applied in medicine, life science and agriculture. Additionally, the current challenges including multiple side reactions and complicated paths, viable solutions along with future directions ahead in this field are also proposed. The coupling electrocatalytic systems provide a green mode for fixing nitrogen cycle bacteria and bring enlightenment to human sustainable development.

Selective C-H Activation of Unprotected Allylamines by Control of Catalyst Speciation

An outstanding challenge in the Pd-catalyzed functionalization of allylamines is the control of stereochemistry. Terminal alkenes preferentially undergo Heck-type reactions, while internal alkenes may undergo a mixture of Heck and C-H activation reactions that give mixtures of stereochemical products. In the case of unprotected allylamines, the challenge in achieving C-H activation is that facile in situ formation of Pd nanoparticles leads to preferential formation of trans rather than cis-substituted products. In this study we have demonstrated the feasibility of using mono-protected amino acid (MPAA) ligands as metal protecting groups to prevent aggregation and reduction, allowing the selective synthesis of free cis-arylated allylamines. This method complements Heck-selective methods, allowing complete stereochemical control over the synthesis of cinnamylamines, an important class of amine that can serve as therapeutics directly or as advanced intermediates. To highlight the utility of the methodology, we have demonstrated rapid access to mu opioid receptor ligands.

Scope and Mechanistic Probe into Asymmetric Synthesis of α-Trisubstituted-α-Tertiary Amines by Rhodium Catalysis

Asymmetric reactions that convert racemic mixtures into enantioenriched amines are of significant importance due to the prevalence of amines in pharmaceuticals, with about 60% of drug candidates containing tertiary amines. Although transition-metal catalyzed allylic substitution processes have been developed to provide access to enantioenriched α-disubstituted allylic amines, enantioselective synthesis of sterically demanding α-tertiary amines with a tetrasubstituted carbon stereocenter remains a major challenge. Herein, we report a chiral diene-ligated rhodium-catalyzed asymmetric substitution of racemic tertiary allylic trichloroacetimidates with aliphatic secondary amines to afford α-trisubstituted-α-tertiary amines. Mechanistic investigation is conducted using synergistic experimental and computational studies. Density functional theory calculations show that the chiral diene-ligated rhodium promotes the ionization of tertiary allylic substrates to form both anti and syn π-allyl intermediates. The anti π-allyl pathway proceeds through a higher energy than the syn π-allyl pathway. The rate of conversion of the less reactive π-allyl intermediate to the more reactive isomer via π-σ-π interconversion was faster than the rate of nucleophilic attack onto the more reactive intermediate. These data imply that the Curtin-Hammett conditions are met in the amination reaction, leading to dynamic kinetic asymmetric transformation. Computational studies also show that hydrogen bonding interactions between β-oxygen of allylic substrate and amine-NH greatly assist the delivery of amine nucleophile onto more hindered internal carbon of the π-allyl intermediate. The synthetic utility of the current methodology is showcased by efficient preparation of α-trisubstituted-α-tertiary amines featuring pharmaceutically relevant secondary amine cores with good yields and excellent selectivities (branched-linear >99:1, up to 99% enantiomeric excess).

Merging of Light/Dark Palladium Catalytic Cycles Enables Multicomponent Tandem Alkyl Heck/Tsuji-Trost Homologative Amination Reaction toward Allylic Amines

A visible light-induced palladium-catalyzed homologative three-component synthesis of allylic amines has been developed. This protocol proceeds via a unique mechanism involving two distinct cycles enabled by the same Pd(0) catalyst: a visible light-induced hybrid radical alkyl Heck reaction between 1,1-dielectrophile and styrene, followed by the "in dark" classical Tsuji-Trost-type allylic substitution reaction. This method works well with a broad range of primary and secondary amines, aryl alkenes, dielectrophiles, and in complex settings. The regiochemistry of the obtained products is primarily governed by the structure of 1,1-dielectrophile. Involvement of π-allyl palladium intermediates allowed for the control of stereoselectivity, which has been demonstrated with up to 95:5 er.

Practical synthesis of allylic amines via nickel-catalysed multicomponent coupling of alkenes, aldehydes, and amides

Molecules with an allylic amine motif provide access to important building blocks and versatile applications of biologically relevant chemical space. The need for diverse allylic amines requires the development of increasingly general and modular multicomponent reactions for allylic amine synthesis. Herein, we report an efficient catalytic multicomponent coupling reaction of simple alkenes, aldehydes, and amides by combining nickel catalysis and Lewis acid catalysis, thus providing a practical, environmentally friendly, and modular protocol to build architecturally complex and functionally diverse allylic amines in a single step. The method is remarkably simple, shows broad functional-group tolerance, and facilitates the synthesis of drug-like allylic amines that are not readily accessible by other methods. The utilization of accessible starting materials and inexpensive Ni(ii) salt as the alternative precatalyst offers a significant practical advantage. In addition, the practicality of the process was also demonstrated in an efficient, gram-scale preparation of the prostaglandin agonist.

Allylic Amination of Highly Substituted Alkenes Enabled by Photoredox Catalysis and Cu(II)-Mediated Radical-Polar Crossover

Allylic amination reactions enable the conversion of alkene feedstocks into value-added products with significant synthetic versatility. Here we describe a method for allylic amination involving photoredox activation and Cu(II)-mediated radical-polar crossover. A range of structurally varied allylic amines can be accessed using this strategy. The regioselectivity of this process is complementary to those of conventional methods for allylic amination.

Cu-based high-entropy two-dimensional oxide as stable and active photothermal catalyst

Cu-based nanocatalysts are the cornerstone of various industrial catalytic processes. Synergistically strengthening the catalytic stability and activity of Cu-based nanocatalysts is an ongoing challenge. Herein, the high-entropy principle is applied to modify the structure of Cu-based nanocatalysts, and a PVP templated method is invented for generally synthesizing six-eleven dissimilar elements as high-entropy two-dimensional (2D) materials. Taking 2D Cu₂Zn₁Al_0.5Ce₅Zr_0.5O_x as an example, the high-entropy structure not only enhances the sintering resistance from 400 °C to 800 °C but also improves its CO₂ hydrogenation activity to a pure CO production rate of 417.2 mmol g^-1 h^-1 at 500 °C, 4 times higher than that of reported advanced catalysts. When 2D Cu₂Zn₁Al_0.5Ce₅Zr_0.5O_x are applied to the photothermal CO₂ hydrogenation, it exhibits a record photochemical energy conversion efficiency of 36.2%, with a CO generation rate of 248.5 mmol g^-1 h^-1 and 571 L of CO yield under ambient sunlight irradiation. The high-entropy 2D materials provide a new route to simultaneously achieve catalytic stability and activity, greatly expanding the application boundaries of photothermal catalysis.

Palladium-Catalyzed Oxidative Amination of Unactivated Olefins with Primary Aliphatic Amines

Direct coupling of unactivated olefins with primary alkylamines is considered to be an efficient but unknown method for the construction of complex amines. Herein we report a catalytic intermolecular oxidative amination of unactivated olefins with primary aliphatic amines based on the combination of a palladium catalyst, a bidentate phosphine ligand, and duroquinone. A range of secondary allylic amines were obtained in good yields with excellent regio- and stereoselectivity. Mechanistic control experiments revealed that the reaction proceeds by allylic C(sp³)-H activation and nucleophilic amination. The utility of the protocol is further demonstrated with the late-stage modification and streamlined synthesis of drug molecules.

A unified approach to benzo[c]phenanthridines via the cascade dual-annulation/formylation of 2-alkynyl/alkenylbenzonitriles

A base-mediated versatile cascade dual-annulation and formylation of 2-alkenyl/alkynylbenzonitriles with 2-methylbenzonitriles has been established for the construction of four different classes of amino and amido substituted benzo[c]phenanthridines and benzo[c]phenanthrolines. The synthesized molecules could be of utmost relevance in pharmaceuticals. The transformation uses the solvent DMF as the formyl source for synthesis of the amido-substituted scaffolds. This transition-metal-free unique strategy enables the formation of multiple C-C and C-N bonds in one pot at room temperature.

N-Allylation of Azoles with Hydrogen Evolution Enabled by Visible-Light Photocatalysis

Direct N-allylation of azoles with hydrogen evolution has been achieved through the synergistic combination of organic photocatalysis and cobalt catalysis. The protocol bypasses stoichiometric oxidants and prefunctionalization of alkenes and produces hydrogen (H₂) as the byproduct. This transformation highlights high step- and atom-economy, high efficiency, and broad functional group tolerance for further derivatization, which opens a door for C-N bond formation that is valuable in heterocyclic chemistry.

Palladium-Catalyzed Branch- and Z-Selective Allylic C-H Amination with Aromatic Amines

Allylamines are important building blocks in the synthesis of bioactive compounds. The direct coupling of allylic C-H bonds and commonly available amines is a major synthetic challenge. An allylic C-H amination of 1,4-dienes has been accomplished by palladium catalysis. With aromatic amines, branch-selective allylic aminations are favored to generate thermodynamically unstable Z-allylamines. In addition, more basic aliphatic cyclic amines can also engage in the reaction, but linear dienyl allylic amines are the major products.

Intertwining Olefin Thianthrenation with Kornblum/Ganem Oxidations: Ene-type Oxidation to Furnish α,β-Unsaturated Carbonyls

A widely applicable, practical, and scalable synthetic method for efficient ene-type double oxidation of alkenes is reported via a two-step alkenyl thianthrenium umpolung/Kornblum-Ganem oxidation strategy. This chemo- and stereoselective procedure allows easy access to various α,β-unsaturated carbonyls that may be otherwise difficult or cumbersome to synthesize by conventional methods. For α-olefins, this metal-free transformation can be tuned according to synthetic needs to produce either the elusive (Z)-unsaturated aldehydes or their (E) counterparts. Moreover, this strategy has enabled streamlined synthesis of distinct butadienyl pheromones and kairomones.

Pd-catalyzed access to mono- and di-fluoroallylic amines from primary anilines

The Pd-catalyzed highly selective synthesis of mono- and di-2-fluoroallylic amines from gem-difluorocyclopropanes and ubiquitous unprotected primary anilines is herein described. Initial kinetic investigations suggest a first order in the gem-difluorocyclopropane substrate, as well as a circa zeroth order in the aniline coupling partner. The newly produced fluoroallylic motifs should find important applications in synthetic as well as medicinal chemistry and stimulate the further development of coupling methods based on strained cyclic building blocks.

Ligand-assisted olefin-switched divergent oxidative Heck cascade with molecular oxygen enabled by self-assembled imines

Divergent oxidative Heck reaction has proven to be reliable for the rapid construction of molecular complexity, while olefins switched the outcome that remained underexplored.

Asymmetric intermolecular allylic C-H amination of alkenes with aliphatic amines

Aliphatic allylic amines are found in a great variety of complex and biorelevant molecules. The direct allylic C-H amination of alkenes serves as the most straightforward method toward these motifs. However, use of widely available internal alkenes with aliphatic amines in this transformation remains a synthetic challenge. In particular, palladium catalysis faces the twin challenges of inefficient coordination of Pd(II) to internal alkenes but excessively tight and therefore inhibitory coordination of Pd(II) by basic aliphatic amines. We report a general solution to these problems. The developed protocol, in contrast to a classical Pd(II/0) scenario, operates through a blue light-induced Pd(0/I/II) manifold with mild aryl bromide oxidant. This open-shell approach also enables enantio- and diastereoselective allylic C-H amination.

Palladium-catalysed selective oxidative amination of olefins with Lewis basic amines

Amines are prominent in natural products, pharmaceutical agents and agrochemicals. Moreover, they are synthetically valuable building blocks for the construction of complex organic molecules and functional materials. However, amines, especially aliphatic and aromatic amines with free N-H bonds, tend to coordinate with transition metals and deactivate the catalyst, posing a tremendous challenge to applying Lewis basic amines in the amination of olefins. Here we present an example of oxidative amination of simple olefins with various Lewis basic amines. The combination of a palladium catalyst, 2,6-dimethyl-1,4-benzoquinone and a phosphorous ligand leads to the efficient synthesis of alkyl and aryl allylamines. A series of allylamines were obtained with good yields and excellent regio- and stereoselectivities. Intramolecular amination to synthesize tetrahydropyrrole and piperidine derivatives was also realized. Mechanistic investigations reveal that the reaction undergoes allylic C(sp³)-H activation and subsequent functionalization.