Copper-Catalyzed Modular Amino Oxygenation of Alkenes: Access to Diverse 1,2-Amino Oxygen-Containing Skeletons

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.

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.

Emerging Trends in Copper-Promoted Radical-Involved C-O Bond Formations

The C-O bond is ubiquitous in biologically active molecules, pharmaceutical agents, and functional materials, thereby making it an important functional group. Consequently, the development of C-O bond-forming reactions using catalytic strategies has become an increasingly important research topic in organic synthesis because more conventional methods involving strong base and acid have many limitations. In contrast to the ionic-pathway-based methods, copper-promoted radical-mediated C-O bond formation is experiencing a surge in research interest owing to a renaissance in free-radical chemistry and photoredox catalysis. This Perspective highlights and appraises state-of-the-art techniques in this burgeoning research field. The contents are organized according to the different reaction types and working models.

Development of New Reactions Driven by N-O Bond Cleavage: from O-Acyl Hydroxylamines to Tetrodotoxin

This Account describes new reactions that have been developed in the Johnson laboratories at UNC Chapel Hill enabled by considerations of N-O bond cleavage. Three main case studies are highlighted: the metal-catalyzed electrophilic amination of O-acyl hydroxyl amines, multihetero-Cope rearrangements driven by O-N bond breakage, and merged dearomatization/N=O cycloadditions for the synthesis of complex 4-aminocyclohexanols such as those found in the natural product tetrodotoxin.

Access to Saturated Oxygen Heterocycles and Lactones via Electrochemical Sulfonylative Oxycyclization of Alkenes with Sulfonyl Hydrazides

A facile electrochemical sulfonylative cycloetherification of linear unsaturated alcohols with sulfonyl hydrazides under mild conditions has been accomplished. This catalyst- and oxidant-free protocol proceeds via electro-oxidation, followed by radical addition, as well as an intramolecular oxygen nucleophilic process. This methodology is compatible with a broad substrate scope and good functional group compatibility, which provides a valuable and convenient synthetic tool for the synthesis of saturated five-, six-, seven-, and eight-membered ring oxygen heterocycles. Furthermore, sulfonylative cycloesterification of linear unsaturated acids toward the lactone products has also been established under this electrochemical system. In addition, control experiments indicated that the N-H bonds of the sulfonyl hydrazide molecule are non-essential.

Photoexcited Palladium-Initiated Remote Desaturation of N-Alkoxypyridinium Salts

1,5-Hydrogen atom transfer (HAT) is an effective strategy to achieve remote desaturation of nonfunctionalized alkanes. Herein, we report a photoinduced remote desaturation reaction of N-alkoxypyridinium salts, which serve as alkoxyl radical precursors. Mechanistic studies show that a single electron transfer between the excited palladium complex and a N-alkoxypyridinium salt initiates a radical chain process leading to desaturation of N-alkoxypyridinium salts. This chain mechanism is supported by the measurement of the quantum yield of this reaction (Φ = 82). This reaction is applicable to a range of N-alkoxypyridinium salts, including some complex molecule-derived ones.

Copper-Catalyzed Amino Radical Tandem Cyclization toward the Synthesis of Indolo-[2,1-a]isoquinolines

We report a convenient process to the synthesis of indolo-[2,1-a]isoquinoline tetracyclic skeletons in one-pot via a low-cost copper-catalyzed tandem amino radical cyclization, in which one C-C bond and one C-N...

Recent Advances in Copper-Catalyzed C-N Bond Formation Involving N-Centered Radicals

C-N bonds are pervasive throughout organic-based materials, natural products, pharmaceutical compounds, and agricultural chemicals. Considering the widespread importance of C-N bonds, the development of greener and more convenient ways to form C-N bonds, especially in late-stage synthesis, has become one of the hottest research goals in synthetic chemistry. Copper-catalyzed radical reactions involving N-centered radicals have emerged as a sustainable and promising approach to build C-N bonds. As a chemically popular and diverse radical species, N-centered radicals have been used for all kinds of reactions for C-N bond formation by taking advantage of their inherently incredible reactive flexibility. Copper is also the most abundant and economic catalyst with the most relevant activity for facilitating the synthesis of valuable compounds. Therefore, the aim of the present Review was to illustrate recent and significant advances in C-N bond formation methods and to understand the unique advantages of copper catalysis in the generation of N-centered radicals since 2016. To provide an ease of understanding for the readers, this Review was organized based on the types of nitrogen sources (amines, amides, sulfonamides, oximes, hydrazones, azides, and tert-butyl nitrite).

1,2-Aminofunctionalization Reactions of Pyridino-Alkynes via Carbophilic Activation

Transition metal-catalyzed 1,2-difunctionalization reactions of alkynes have emerged as a powerful tool to forge carbon-carbon and carbon-heteroatom bonds for the rapid synthesis of polyfunctionalized molecular scaffolds. In this regard, our group has persistently been developing transition metal-mediated 1,2-aminofunctionalization reactions of alkynes through a rationally designed pyridino-alkyne core by utilizing the carbophilic activation strategy. In this account, we present an array of such 1,2-aminofunctionalization reactions which have been successfully executed on this core to afford important polycyclic frameworks such as functionalized quinalizinones, pyridinium oxazole dyads (PODs), N-doped polycyclic aromatic hydrocarbons (PAHs), N-doped spiro-PAHs. Additionally, the synthesis of phosphine ligated gold complexes bearing pyrido-isoquinoline scaffold from the pyridino-alkynes will be discussed briefly.

Copper-Catalyzed 3-Positional Amination of 2-Azulenols with O-Benzoylhydroxylamines

A copper-catalyzed ortho-selective amination of 2-azulenols with O-benzoylhydroxylamines (RR'N-OBz) to synthesize ortho-aminoazulenols is reported. A wide range of functional groups on amines are compatible, furnishing the corresponding amino-azulene derivatives in moderate to good yields. The further synthetic elaboration using 3-amino-2-azulenols as starting materials is demonstrated.

Pd-Catalyzed Alkene Diamination Reactions with O-Benzoylhydroxylamine Electrophiles: Evidence Supporting a Pd(II/IV) Catalytic Cycle, the Role of 2,4-Pentanedione Derivatives as Ligands, and Expanded Substrate Scope

This article describes continued studies on Pd-catalyzed alkene diamination reactions between N-allylguanidines or ureas and O-benzoylhydroxylamine derivatives, which serve as N-centered electrophiles. The transformations generate cyclic guanidines and ureas bearing dialkylaminomethyl groups in moderate to good yield. We describe new mechanistic experiments that have led to a revised mechanistic hypothesis that involves a key oxidative addition of the electrophile to a Pd^II complex, followed by reductive elimination from Pd^IV to form the alkyl carbon-nitrogen bond. In addition, we demonstrate that acac, not phosphine, serves as a key ligand for palladium. Moreover, simple acac derivatives bearing substituted aryl groups outperform acac in the catalytic reactions, and phosphines inhibit catalysis in many cases. These discoveries have led to a significant expansion in the scope of this chemistry, which now allows for the coupling of a variety of cyclic amines, acyclic secondary amines, and primary amines. In addition, we also demonstrate that these new conditions allow for the use of amide nucleophiles, in addition to guanidines and ureas.

Copper-Catalyzed Aminoheteroarylation of Unactivated Alkenes through Distal Heteroaryl Migration

We report a copper-catalyzed aminoheteroarylation of unactivated alkenes to access valuable heteroarylethylamine motif. The developed reaction features a copper-catalyzed intermolecular electrophilic amination of the alkenes followed by a migratory heteroarylation. The method applies on alcohol-, amide-, and ether-containing alkenes, overcoming the common requirement of a hydroxyl motif in previous migratory difunctionalization reactions. This reaction is effective for the introduction of diverse aliphatic amines and has good functional group tolerance, which is particularly useful for richly functionalized heteroarenes. This migration-involved reaction was found well suited as a powerful ring expansion approach for the construction of medium-sized rings that are in great demand in medicinal chemistry.

Chiral Hypervalent Iodine Catalysis Enables an Unusual Regiodivergent Intermolecular Olefin Aminooxygenation

A novel iodide-catalyzed intermolecular aminooxygenation strategy is described here. Amide is used as the O- and N- source to probe for regiocontrol strategies. Notably, simple additives can be selectively introduced to achieve regiodivergent oxyamination processes for electronically activated alkenes while being regio-complementary for unactivated alkenes. Our preliminary data demonstrates that this regiocontrol strategy based on nucleophile can also be applied in asymmetric processes using chiral hypervalent iodine catalysis.

External-oxidant-free amino-benzoyloxylation of unactivated alkenes of unsaturated ketoximes with O-benzoylhydroxylamines

A new copper-catalyzed two-component amino-benzoyloxylation of unactivated alkenes of unsaturated ketoximes with O-benzoylhydroxylamines as the benzoyloxy sources is developed. Chemoselectivity of this method toward amino-benzoyloxylation or oxy-benzoyloxylation of alkenyl ketoximes relies on the position of the tethered olefins, and provides an external-oxidant-free alkene difunctionalization route that directly utilizes O-benzoylhydroxylamines as the benzoyloxy radical precursors and internal oxidants for the divergent synthesis of cyclic nitrones and isoxazolines.

Beyond osmium: progress in 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes

Olefin 1,2-difunctionalization has emerged as a popular strategy within modern synthetic chemistry for the synthesis of vicinal amino alcohols and derivatives. The advantage of this approach is the single-step simplicity for rapid diversification, feedstock nature of the olefin starting materials, and the possible modularity of the components. Although there is a vast number of possible iterations of 1,2-olefin difunctionalization, 1,2-amino oxygenation is of particular interest due to the prevalence of both oxygen and nitrogen within pharmaceuticals, natural products, agrochemicals, and synthetic ligands. The Sharpless amino hydroxylation provided seminal results in this field and displayed the value in achieving methods of this nature. However, a vast number of new and novel methods have emerged in recent decades. This review provides a comprehensive review of modern advances in accomplishing 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes that move beyond osmium to a range of other transition metals and more modern strategies such as electrochemical, photochemical, and biochemical reactivity.

Iodoarene-Catalyzed Oxyamination of Unactivated Alkenes to Synthesize 5-Imino-2-Tetrahydrofuranyl Methanamine Derivatives

Reported here is the room-temperature metal-free iodoarene-catalyzed oxyamination of unactivated alkenes. In this process, the alkenes are difunctionalized by the oxygen atom of the amide group and the nitrogen in an exogenous HNTs₂ molecule. This mild and open-air reaction provided an efficient synthesis to N-bistosyl-substituted 5-imino-2-tetrahydrofuranyl methanamine derivatives, which are important motifs in drug development and biological studies. Mechanistic study based on experiments and density functional theory calculations showed that this transformation proceeds via activation of the substrate alkene by an in situ generated cationic iodonium(III) intermediate, which is subsequently attacked by an oxygen atom (instead of nitrogen) of amides to form a five-membered ring intermediate. Finally, this intermediate undergoes an S_N2 reaction by NTs₂ as the nucleophile to give the oxygen and nitrogen difunctionalized 5-imino-2-tetrahydrofuranyl methanamine product. An asymmetric variant of the present alkene oxyamination using chiral iodoarenes as catalysts also gave promising results for some of the substrates.

Copper-Catalyzed Decarboxylative Functionalization of Conjugated β,γ-Unsaturated Carboxylic Acids

Copper-catalyzed decarboxylative coupling reactions of conjugated β,γ-unsaturated carboxylic acids have been achieved for allylic amination, alkylation, sulfonylation, and phosphinoylation. This approach was effective for a broad scope of amino, alkyl, sulfonyl, and phosphinoyl radical precursors as well as various conjugated β,γ-unsaturated carboxylic acids. These reactions also feature high regioselectivity, good functional group tolerance, and simple operation procedure. Mechanistic studies show that the reaction proceeds via copper-catalyzed electrophilic addition onto an olefin followed by decarboxylation, with radical intermediates involved. These insights present a modular and powerful strategy to access versatilely functionalized allyl-containing skeletons from readily available and stable carboxylic acids.

Copper-Catalyzed 1,2-Aminocyanation of Unactivated Alkenes via Cyano Migration

A copper-catalyzed aminocyanation of alkenes has been achieved through distal cyano migration using O-benzoylhydroxylamines and N-fluorobenzenesulfonimides. This method offers a rapid approach to generate diverse β-amino and β-sulfonimido nitriles. These reactions feature mild conditions, tolerance of sensitive functional groups, and excellent regioselectivity. Mechanistic studies suggest that these transformations are initiated by a copper-catalyzed amination step followed by a cyano migration step.

Preparation of Tertiary Amines from Tris(2-cyanoethyl)amine Using Three Successive Cobalt-Catalyzed Electrophilic Aminations with Organozinc Halides

We report a stepwise preparation of triple alkylated or arylated tertiary amines, starting from commercially available tris(2-cyanoethyl)amine using three successive reaction sequences involving a selective oxidation (formation of an N-oxide followed by a Cope elimination) leading to an intermediate hydroxylamine, a benzoylation, and a cobalt-catalyzed electrophilic amination with organozinc halides.

Alkene Syn- and Anti-Oxyamination with Malonoyl Peroxides

Malonoyl peroxide 6 is an effective reagent for the syn- or anti-oxyamination of alkenes. Reaction of 6 and an alkene in the presence of O-tert-butyl-N-tosylcarbamate (R³ = CO₂^tBu) leads to the anti-oxyaminated product in up to 99% yield. Use of O-methyl-N-tosyl carbamate (R³ = CO₂Me) as the nitrogen nucleophile followed by treatment of the product with trifluoroacetic acid leads to the syn-oxyaminated product in up to 77% yield. Mechanisms consistent with the observed selectivities are proposed.

Oxyamination of Unactivated Alkenes with Electron-Rich Amines and Acids via a Catalytic Triiodide Intermediate

An aerobic catalytic oxidation process is described for the olefin oxyamination using acids and primary amines as the sources of O and N. Our mechanistic findings point to the formation of triiodide as a critical catalytic intermediate to account for the tolerance of electron-rich nucleophiles. This dual iodide and copper catalytic system is suitable for a formal [5+1] annulation process to access valuable lactam structures and highlighted by the synthesis of the pharmaceutical Zamifenacin.

Iron-Mediated Electrophilic Amination of Organozinc Halides using Organic Azides

A wide range of alkyl‐, aryl‐ and heteroarylzinc halides were aminated with highly functionalized alkyl, aryl, and heterocyclic azides. The reaction proceeds smoothly at 50 °C within 1 h in the presence of FeCl₃ (0.5 equiv) to furnish the corresponding secondary amines in good yields. This method was extended to peptidic azides and provided the arylated substrates with full retention of configuration. To demonstrate the utility of this reaction, we prepared two amine derivatives of pharmaceutical relevance using this iron‐mediated electrophilic amination as the key step.

Copper-catalyzed regioselective sulfonylcyanations of vinylarenes

A set of copper-catalyzed sulfonylcyanations of vinylarenes with readily accessible arylsulfonyl chlorides and trimethyl cyanide was achieved, providing a streamlined route to various decorated β-sulfonyl nitriles with good regioselectivity and functional group tolerance.

Copper-Catalyzed 1,2-Amino Oxygenation of 1,3-Dienes: A Chemo-, Regio-, and Site-Selective Three-Component Reaction with O-Acylhydroxylamines and Carboxylic Acids

A three-component reaction for 1,2-amino oxygenation of 1,3-dienes has been achieved using O-acyl hydroxylamines and carboxylic acids. The reaction occurs through copper-catalyzed amination of olefins followed by nucleophilic addition of carboxylic acids, offering high levels of chemo-, regio-, and site-selectivity. The method is effective for both terminal and internal 1,3-dienes, including those bearing multiple, unsymmetrical substituents. The amino oxygenation conditions also exhibited remarkable selectivity toward 1,3-dienes over alkenes, good tolerance of sensitive functional groups, and reliable scalability.

Copper(II)-Catalyzed Alkene Aminosulfonylation with Sodium Sulfinates For the Synthesis of Sulfonylated Pyrrolidones

A copper-catalyzed direct aminosulfonylation of unactivated alkenes with sodium sulfinates for the efficient synthesis of sulfonylated pyrrolidones is described. This reaction features good functional group tolerance and wide substrate scope, providing an efficient and straightforward protocol to access this kind of pyrrolidones. Moreover, preliminary mechanistic investigations disclosed that a free-radical pathway might be invovled in the process.