Pyrrolidine and piperidine formation via copper(II) carboxylate-promoted intramolecular carboamination of unactivated olefins: diastereoselectivity and mechanism

Cu-Catalyzed Three-Component Alkene Carboamination: Mechanistic Insights and Rational Design to Overcome Limitations

Herein, we report mechanistic investigations into the Cu-catalyzed three-component carboamination of alkenes with α-halo carbonyls and aryl amines via an oxocarbenium intermediate. Monitoring the reaction reveals the formation of transient atom transfer radical addition (ATRA) intermediates with both electron-neutral and deficient vinyl arenes as well as unactivated alkenes. Based on our experimental studies and density functional theory calculations, the oxocarbenium is generated through atom transfer and subsequent intramolecular substitution. Further, mechanistic factors that dictate the regioselectivity of the nucleophilic attack onto the oxocarbenium to afford the γ-amino ester, γ-iminolactone, or γ-lactone are discussed. A strategy to overcome scope limitation with respect to unactivated alkenes is developed using the mechanistic insights gained herein. Finally, we demonstrate that under modified conditions, our Cu catalyst enables the ATRA reaction between a variety of alkyl halides and vinyl arenes/α-olefins, and we present a one-pot, two-step carbofunctionalization with an array of nucleophiles through ATRA/SN2.

Organic Synthesis Using Nitroxides

Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.

Recent Advances in 1,2-Amino(hetero)arylation of Alkenes

Alkene amino(hetero)arylation presents a highly efficient and straightforward strategy for direct installation of amino groups and heteroaryl rings across a double bond simultaneously. An extensive array of practical transformations has been developed via alkene difunctionalization approach to access a broad range of medicinally valuable (hetero)arylethylamine motifs. This review presents recent progress in 1,2-amino(hetero)arylation of alkenes organized in three different modes. First, intramolecular transformations employing C, N-tethered alkenes will be introduced. Next, two-component reactions will be discussed with different combination of precursors, N-tethered alkenes and external aryl precursor, C-tethered alkenes and external amine precursor, or C, N-tethered reagents, and alkenes. Last, three-component intermolecular amino(hetero)arylation reactions will be covered.

Copper-Catalyzed Cyclization/Dimerization of Tryptamines with O2/Air as the Sole Oxidant: Direct Access to Complex Bispyrrolidino[2,3-b]indoline

The first transition metal catalytic one-step synthesis of the 3a, 3a'-bispyrrolidino [2,3-b] indoline scaffold via tandem cyclization/dimerization of tryptamines has been realized with the environmentally friendly O₂/air as the sole oxidant. Different from the traditional direct oxidation of indole "N-H" group by excess amount of metal salts, a copper-catalyzed oxidative cyclization reaction is developed for the formation of the radical pyrrolidinoindoline intermediate in the current strategy. The robustness and practicality of this methodology is demonstrated by the step-economic, divergent total synthesis of natural products (±)-folicanthine and meso-folicanthine.

Copper-catalyzed aerobic oxidative radical alkoxycyclization of tryptamines to access 3-alkoxypyrroloindolines

We report a copper-catalyzed alkoxycyclization of tryptamine derivatives with O₂ as the sole oxidant, leading to a variety of C3a-alkoxypyrroloindolines in good yields with high diastereoselectivities. This reaction involves an interesting double catalytic cycle in which copper-catalyzed carboamination cyclization is favored to form the C-3 radical pyrrolidinoindoline intermediate, then a copper-catalytic radical alkoxylation reaction proceeds smoothly.

Three-component photoredox 1,2-alkylamination of styrenes with alkanes and nitrogen nucleophiles via C(sp3)–H bond cleavage

A three-component photoredox 1,2-alkylamination of styrenes involving functionalization of C(sp3)–H bonds in alkyl halides instead of functionalization of C-halogen bonds is disclosed.

Recent developments in the difunctionalization of alkenes with C–N bond formation

Various alkene difunctionalization reactions involving nitridization, diamination, azidation, oxyamination, carboamination, aminohalogenation, and nitration are introduced in this review.

Copper-catalysed radical reactions of alkenes, alkynes and cyclopropanes with N-F reagents

The mild generation of nitrogen-centred radicals from N-F reagents has become a convenient synthetic tool. This methodology provides access to the aminative difunctionalisation of alkenes and alkynes and the radical ring-opening of cyclopropanes, among other similar transformations. This review article aims to provide an overview of recent developments of such processes involving radical reactions and N-F reagents using copper-based catalysts.

Crystal structure of 1-[(4-methylbenzene)sulfonyl]pyrrolidine

The mol-ecular structure of the title compound, C11H15NO2S, features a sulfonamide group with S=O bond lengths of 1.4357 (16) and 1.4349 (16) Å, an S-N bond length of 1.625 (2) Å, and an S-C bond length of 1.770 (2) Å. When viewing the mol-ecule down the S-N bond, both N-C bonds of the pyrrolidine ring are oriented gauche to the S-C bond with torsion angles of -65.6 (2)° and 76.2 (2)°. The crystal structure features both intra- and inter-molecular C-H⋯O hydrogen bonds, as well as inter-molecular C-H⋯π and π-π inter-actions, leading to the formation of sheets parallel to the ac plane.

Regioselective/electro-oxidative intermolecular [3 + 2] annulation for the preparation of indolines

Compared with the reported intramolecular electro-oxidative cyclization of alkenyl amines or vinyl anilines for the preparation of pyrrolidines or indolines, the intermolecular version is less studied. Herein, this electrochemical intermolecular oxidative annulation of anilines and alkenes for the preparation of indolines proceeded under external oxidant-free conditions. The most noteworthy achievement of our work is the facile generation of indolines with quaternary centers at the 2-position. In addition, alkenes and anilines bearing various functional groups can be well tolerated. Remarkably, electrolyte-free conditions were used in an electrochemical flow cell, which shows the application potential of this method.

Changing stereoselectivity and regioselectivity in copper(i)-catalyzed 5-exo cyclization by chelation and rigidity in aminoalkyl radicals: synthesis towards diverse bioactive N-heterocycles

Chelation, rigidity and carbon-radical positions in aminoalkyl precursors disturb the usual 2,4-trans diastereoselectivity and 5-exo mode in Cu(i)-catalyzed ATRC.

Preparation of cyclic imides from alkene-tethered amides: application of homogeneous Cu(ii) catalytic systems

A Cu-based homogeneous catalytic system was proposed for the preparation of imides from alkene-tethered amides. Here, O₂ acted as a terminal oxidant and a cheap and easily available oxygen source. The cleavage of C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds and the formation of C–N bonds were catalyzed by Cu(ii) salts with proper nitrogen-containing ligands under 100 °C. The synthesis approach has potential applications in pharmaceutical syntheses. Moreover, scaled-up experiments confirmed the practical applicability.

A catalytic system comprising Cu(ii) and a nitrogen-based ligand for the oxygenation and cyclization of alkene-tethered amides.

External Oxidant-Dependent Reactivity Switch in Copper-Mediated Intramolecular Carboamination of Alkynes: Access to a Different Class of Fluorescent Ionic Nitrogen-Doped Polycyclic Aromatic Hydrocarbons

An interesting case of external oxidant-controlled reactivity switch leading to a divergent set of ionic nitrogen-doped polycyclic aromatic hydrocarbons (N-doped PAHs), is presented here, which is quite unrecognized in copper-mediated reactions. In the current scenario, from the same pyridino-alkyne substrates, the use of the external oxidant PhI(OAc)₂, in combination with Cu(OTf)₂, gave N-doped spiro-PAHs via a dearomative 1,2-carboamination process; whereas, without the use of oxidant, an alkyne/azadiene [4 + 2]-cycloaddition cascade occurred to exclusively afford ionic N-doped PAHs. These newly synthesized N-doped PAHs further exhibit tunable emissions, as well as excellent quantum efficiencies.

Formal Aza-Wacker Cyclization by Tandem Electrochemical Oxidation and Copper Catalysis

In oxidative electrochemical organic synthesis, radical intermediates are often oxidized to cations on the way to final product formation. Herein, we describe an approach to transform electrochemically generated organic radical intermediates into neutral products by reaction with a metal catalyst. This approach combines electrochemical oxidation with Cu catalysis to effect formal aza-Wacker cyclization of internal alkenes. The Cu catalyst is essential for transforming secondary and primary alkyl radical intermediates into alkenes. A wide range of 5-membered N-heterocycles including oxazolidinone, imidazolidinone, thiazolidinone, pyrrolidinone, and isoindolinone can be prepared under mild conditions.

Synthesis of acyloxyl pyrazolines by copper-mediated aminoacyloxylation of unsaturated ketohydrazones

An efficient and step-economical copper-mediated intra-/intermolecular aminoacyloxylation of β,γ-unsaturated hydrazones has been developed. Copper carboxylates serve as both reaction promoters and carboxylate sources in these easily conducted reactions. This method provides straightforward access to diversely useful acyloxyl pyrazolines, which are hard to access traditionally, in good to excellent yields.

Intermolecular Anti-Markovnikov Hydroamination of Unactivated Alkenes with Sulfonamides Enabled by Proton-Coupled Electron Transfer

Here we report a catalytic method for the intermolecular anti-Markovnikov hydroamination of unactivated alkenes using primary and secondary sulfonamides. These reactions occur at room temperature under visible light irradiation and are jointly catalyzed by an iridium(III) photocatalyst, a dialkyl phosphate base, and a thiol hydrogen atom donor. Reaction outcomes are consistent with the intermediacy of an N-centered sulfonamidyl radical generated via proton-coupled electron transfer activation of the sulfonamide N-H bond. Studies outlining the synthetic scope (>60 examples) and mechanistic features of the reaction are presented.

A new class of N-doped ionic PAHsviaintramolecular [4+2]-cycloaddition between arylpyridines and alkynes

Reported herein, for the first time, is a copper-promoted intramolecular [4+2]-cycloaddition cascade to access ionic N-doped polycyclic aromatic hydrocarbons (PAHs) with tunable emission wavelengths.

Diastereoselective C-H Bond Amination for Disubstituted Pyrrolidines

We report herein the improved diastereoselective synthesis of 2,5-disubstituted pyrrolidines from aliphatic azides. Experimental and theoretical studies of the C-H amination reaction mediated by the iron dipyrrinato complex (Ad L)FeCl(OEt2 ) provided a model for diastereoinduction and allowed for systematic variation of the catalyst to enhance selectivity. Among the iron alkoxide and aryloxide catalysts evaluated, the iron phenoxide complex exhibited superior performance towards the generation of syn 2,5-disubstituted pyrrolidines with high diastereoselectivity.

Copper-catalyzed aminoalkynylation of alkenes with hypervalent iodine reagents

A copper-catalyzed aminoalkynylation of alkenes is achieved with ethynylbenziodoxolone (EBX) reagents under mild conditions with only 1 mol% copper catalyst. This transformation allows for rapid construction of diverse important azahetereocycles and installation of valuable alkyne groups in one step. The developed method features remarkable substrate scope for both terminal and internal alkenes as well as different alkynyl groups, presenting great potential for broad applications in synthesis, bioconjugation, and molecular imaging.

Stereoselective and Regioselective Synthesis of Heterocycles via Copper-Catalyzed Additions of Amine Derivatives and Alcohols to Alkenes

This Perspective describes the development of a family of copper(II)-catalyzed alkene difunctionalization reactions that enable stereoselective addition of amine derivatives and alcohols onto pendant unactivated alkenes to provide a range of valuable saturated nitrogen and oxygen heterocycles. 2-Vinylanilines and related substrates undergo alternative oxidative amination or allylic amination pathways, and these reactions will also be discussed. The involvement of both polar and radical steps in the reaction mechanisms have been implicated. Major product formation is a function of the lowest energy pathway, which in turn is a function of structural aspects of the various reaction components.

Copper-Catalyzed Alkene Aminoazidation as a Rapid Entry to 1,2-Diamines and Installation of an Azide Reporter onto Azahetereocycles

A copper-catalyzed aminoazidation of unactivated alkenes is achieved for the synthesis of versatile unsymmetrical 1,2-diamine derivatives. This transformation offers an effective approach to installing an amide and an azide from two diffenent amino precursors onto both terminal and internal alkenes, with remarkable regio- and stereoselectivity. Mechanistic studies show that this diamination reaction proceeds via a nucleophilic amino cyclization followed by an intermolecular C-N bond formation using electrophilic azidoiodinane. This pathway differs from previous azidoiodinane-initiated alkene functionalization, suggesting new reactivity of azidoiodinane. Furthermore, this aminoazidation reaction provides an efficient strategy to introduce azide, one of the most useful chemical reporters, onto a broad range of bioactive azaheterocycles, offering new opportunities in bioorthogonal chemistry and biological studies. Rapid syntheses of 5-HT2C agonist, (-)-enduracididine and azido-cholesterol derivatives demonstrate broad applications of this method in organic synthesis, medicinal chemistry, and chemical biology.

Iterative direct C(sp3)–H functionalization of amines: diastereoselective divergent syntheses of α,α′-disubstituted alicyclic amines

Facile access to the syn-α,α′-disubstituted N-heterocycles via iterative C–H oxygenation and C–C bond formation.

Copper-Catalyzed Intramolecular Oxidative Amination of Unactivated Internal Alkenes

A copper-catalyzed oxidative amination of unactivated internal alkenes has been developed. The Wacker-type oxidative alkene amination reaction is traditionally catalyzed by a palladium through a mechanism involving aminopalladation and β-hydride elimination. Replacing the precious and scarce palladium with a cheap and abundant copper for this transformation has been challenging because of the difficulty associated with the aminocupration of internal alkenes. The combination of a simple copper salt, without additional ligand, as the catalyst and Dess-Martin periodinane as the oxidant, promotes efficiently the oxidative amination of allylic carbamates and ureas bearing di- and trisubstituted alkenes leading to oxazolidinones and imidazolidinones. Preliminary mechanistic studies suggested a hybrid radical-organometallic mechanism involving an amidyl radical cyclization to form the key C-N bond.

Copper-catalyzed aminooxygenation of styrenes with N-fluorobenzenesulfonimide and N-hydroxyphthalimide derivatives

A copper-catalyzed aminooxygenation reaction of styrenes with N-fluorobenzenesulfonimide and N-hydroxyphthalimide derivatives has been developed. The aminooxygenation product could be converted into the corresponding alcohol or free amine through the cleavage of the N–O or C–N bond of the N-hydroxyphthalimide moiety.

CCC-NHC Pincer Zr Diamido Complexes: Synthesis, Characterisation, and Catalytic Activity in Hydroamination/Cyclisation of Unactivated Amino-Alkenes, -Alkynes, and Allenes

2-(1,3-Bis-3′-butylimidazol-1′-yl-2′-ylidene)phenylene)bis(dimethylamido) iodo zirconium(iv) (3) and 2-(1,3-bis-3′-butylimidazol-1′-yl-2′-ylidene)phenylene)bis (dimethylamido) bromo zirconium(iv) (4), have been prepared via a modification of the solvent and stoichiometry from the previously reported methodology. The reactivity of 3 and 4 in hydroamination/cyclisation is reported. Both diamido complexes have been found to improve catalytic activity as compared with the previously reported mono-amido analogues. Complexes 3 and 4 were observed to be selective for primary amines over secondary amines in hydroamination/cyclisation. The lack of reactivity with secondary amines is consistent with a mechanism involving requisite formation of a Zr-imido intermediate.

A visible-light photocatalytic N-radical cascade of hydrazones for the synthesis of dihydropyrazole-fused benzosultams

An efficient N-centred radical 5-exo cyclization/addition/aromatization cascade by cooperative visible light photoredox and cobalt catalysis is described, giving dihydropyrazole-fused benzosultams in satisfactory yields.

Intermolecular addition reactions of N-alkyl-N-chlorosulfonamides to unsaturated compounds

N-Alkyl-N-chlorosulfonamides add to alkenes under copper(I) catalysis. In reactions of styrene derivatives with terminal double bonds the addition products were obtained in excellent yield and high regioselectivity. Lower yields are obtained in addition reactions to non-aromatic alkenes. The reaction most likely proceeds via a redox catalysis and amidyl radicals, a concerted mechanism has been ruled out and a polar mechanism via chloronium ions would lead to the opposite regiochemistry.

Palladium-Catalyzed Alkene Carboamination Reactions of Electron-Poor Nitrogen Nucleophiles

Modified reaction conditions that facilitate Pd-catalyzed alkene carboamination reactions of electron-deficient nitrogen nucleophiles are reported. Pent-4-enylamine derivatives bearing N-tosyl or N-trifluoroacetyl groups are coupled with aryl triflates to afford substituted pyrrolidines in good yield. These reactions proceed via a mechanism involving anti-aminopalladation of the alkene, which differs from previously reported analogous reactions of N-aryl and N-boc pentenylamines. The application of these conditions to a formal synthesis of (±)-aphanorphine is also described.

CuX2-mediated oxybromination/aminochlorination of unsaturated amides: synthesis of iminolactones and lactams

A CuX₂-mediated halocyclization of γ,δ-unsaturated amides for the synthesis of functionalized iminolactones and lactams respectively is described.

6-Azabicyclo[3.2.1]octanes Via Copper-Catalyzed Enantioselective Alkene Carboamination

Bridged bicyclic rings containing nitrogen heterocycles are important motifs in bioactive small organic molecules. An enantioselective copper-catalyzed alkene carboamination reaction that creates bridged heterocycles is reported herein. Two new rings are formed in this alkene carboamination reaction where N-sulfonyl-2-aryl-4-pentenamines are converted to 6-azabicyclo[3.2.1]octanes using [Ph-Box-Cu](OTf)₂ or related catalysts in the presence of MnO₂ as stoichiometric oxidant in moderate to good yields and generally excellent enantioselectivities. Two new stereocenters are formed in the reaction, and the C-C bond-forming arene addition is a net C-H functionalization.

Intramolecular aminocyanation of alkenes by N-CN bond cleavage

A metal-free, Lewis acid promoted intramolecular aminocyanation of alkenes was developed. B(C6F5)3 activates N-sulfonyl cyanamides, thus leading to a formal cleavage of the N-CN bonds in conjunction with vicinal addition of sulfonamide and nitrile groups across an alkene. This method enables atom-economical access to indolines and tetrahydroquinolines in excellent yields, and provides a complementary strategy for regioselective alkene difunctionalizations with sulfonamide and nitrile groups. Labeling experiments with (13)C suggest a fully intramolecular cyclization pattern due to the lack of label scrambling in double crossover experiments. Catalysis with Lewis acid is realized and the reaction can be conducted under air.