Aerobic Oxidative Amination Research Articles

Palladium Catalyzed Aerobic Oxidative Amination of Alkenes

AbstractAmines are widely applied in the chemical and pharmaceutical industries, and the development of synthetic methods for their preparation is driven by their importance. The amination of alkenes is a direct and efficient method for the construction of amines, of which oxidative amination is more valuable because it can give the desired products with greater functionality and flexibility. In oxidative amination, using molecular oxygen (O2) as a terminal oxidant has promising industrial application prospects. In recent years, the palladium‐catalyzed aerobic oxidation of alkenes has seen significant progress, and its related research has also been extended to the aerobic oxidative amination of alkenes. The corresponding oxidation systems have been developed from early research involving the introduction of cocatalysts to the more recent systems which utilize auxiliary ligands instead of cocatalysts. In this review, the advancements in the palladium‐catalyzed aerobic oxidative amination of monoalkenes and conjugated dienes over the last two decades are discussed, with emphasis on aerobic oxidation process and their associated mechanisms.

Green, versatile, and scale-up synthesis of amides by aerobic oxidative amination over Ag2O/P-C3N4 photocatalyst

Being extensively applied in various fields of chemistry and chemical industry, the development of a green and versatile method for the synthesis of amides is in line with the demand of sustainable chemistry. Herein, a direct, highly selective, and scale-up (5–20 mmol) method for photocatalytic synthesis of amides through aerobic oxidative amination of alcohols with amines was developed under visible light, room temperature, using air as the oxidant. Benefiting from the adsorption of sodium hemiaminal on catalyst lengthens the CH bond (1.148 Å), this novel process is feasible for a broad range of functionlized amides (69 examples), especially those for drug manufacture (e.g., moclobemide and pipobroman). Imines was almost prevented with excellent amide selectivity up to 99 % could be ascribed to the low energy barrier for hemiaminal dehydrogenation while that for dehydration is high (2.13 eV). This green and efficient protocol represents an ideal alternative to the currently known methods.

A Cu(ii) metal-organic framework with significant H2 and CO2 storage capacity and heterogeneous catalysis for the aerobic oxidative amination of C(sp3)-H bonds and Biginelli reactions.

A Cu(ii) metal-organic framework, {[Cu2(L)(H2O)2]·(5DMF)(4H2O)}n (1), has been synthesized using an angular tetracarboxylic acid ligand (H4L) incorporating both trifluoromethyl (-CF3) and amine (-NH2) groups. Notably, the framework possesses high water and thermal stability. At atmospheric pressure, the activated framework 1' exhibits substantially high amounts of CO2 (35.5 and 20.8 wt% at 273 and 298 K respectively) and H2 (1.72 wt% at 77 K) adsorption. Also, 1' exhibits excellent catalytic activity for the condensation-cyclization reaction between 2-benzoyl pyridine and different benzylamines via oxidative amination of the C(sp3)-H bond to form 1,3-diarylated imidazo[1,5-a]pyridines under mild aerobic conditions. In addition to this, 1' shows excellent heterogeneous catalytic activity in Biginelli reactions. The solid catalyst could be recycled several times without significant loss in the catalytic activities.

Cu/Ag‐Cocatalyzed Aerobic Oxidative Amination and CuCl2‐Mediated Aerobic Oxidative Chloroamination of Maleimides

An efficient Cu(OAc)2/Ag2CO3‐cocatalyzed approach for the synthesis of 3‐aminomaleimides and 3‐amino‐4‐indolylmaleimides has been developed with satisfactory yields. A series of primary and secondary amines are compatible with this reaction. In addition, treatment of maleimides with primary amines using 1 equiv. of CuCl2 leads to the formation of chloroamination products such as 3‐amino‐4‐chloromaleimides by a radical‐type mechanism.

ChemInform Abstract: Copper‐Catalyzed Aerobic Oxidative Amination of sp3C—H Bonds: Efficient Synthesis of 2‐Hetarylquinazolin‐4(3H)‐ones.

An efficient synthesis of 2-hetarylquinazolin-4(3H)-ones via copper-catalyzed direct aerobic oxidative amination of sp3C–H bonds has been developed. This tandem oxidation–amination–cyclization transformation represents a straightforward protocol to prepare 2-hetaryl-substituted quinazolinones from easily available 2-aminobenzamides and (2-azaaryl)methanes.

Copper-catalyzed aerobic oxidative amination of sp3 C-H bonds: efficient synthesis of 2-hetarylquinazolin-4(3H)-ones.

An efficient synthesis of 2-hetarylquinazolin-4(3H)-ones via copper-catalyzed direct aerobic oxidative amination of sp(3)C-H bonds has been developed. This tandem oxidation-amination-cyclization transformation represents a straightforward protocol to prepare 2-hetaryl-substituted quinazolinones from easily available 2-aminobenzamides and (2-azaaryl)methanes.

Copper(II)‐Catalyzed Aerobic Oxidative Coupling between Chalcone and 2‐Aminopyridine via CH Amination: An Expedient Synthesis of 3‐Aroylimidazo[1,2‐a]pyridines

AbstractA simple and efficient protocol has been developed for the synthesis of 3‐aroylimidazopyridines via copper(II) acetate‐catalyzed aerobic oxidative amination. A library of 3‐aroylimidazopyridines was synthesized from readily accessible chalcones and 2‐aminopyridines with high yields and regioselectivity. The reaction proceeds through a tandem Michael addition followed by an intramolecular oxidative amination. The successful application of this methodology for a gram‐scale reaction indicates its potential for bulk synthesis.magnified image

Palladium Catalyzed Aryl C-H Amination with O2 via In Situ Formation of Peroxide-Based Oxidant(s) from Dioxane.

(DAF)Pd(OAc)2 (DAF = 4,5-diazafluorenone) catalyzes aerobic intramolecular aryl C-H amination with N-benzenesulfonyl-2-aminobiphenyl in dioxane to afford the corresponding carbazole product. Mechanistic studies show that the reaction involves in situ generation of peroxide species from 1,4-dioxane and O2, and the reaction further benefits from the presence of glycolic acid, an oxidative decomposition product of dioxane. An induction period observed for the formation of the carbazole product correlates with the formation of 1,4-dioxan-2-hydroperoxide via autoxidation of 1,4-dioxane, and the in situ-generated peroxide is proposed to serve as the reactive oxidant in the reaction. These findings have important implications for the palladium-catalyzed aerobic oxidation reactions conducted in ethereal solvents.

ChemInform Abstract: Copper‐Catalyzed Aerobic Oxidative Amination of Arylboronic Acid with Aminal under Base‐Free Conditions.

AbstractAmination is carried out in the presence of air with symmetrical aminals to give the products in moderate yields.

Copper-Catalyzed Aerobic Oxidative Amination of Arylboronic Acid with Aminal under Base-Free Conditions

A new process involving copper-catalyzed oxidative amination reaction of various arylboronic acids with aminals under mild conditions has been developed. The key copper-amide species involved in the C–N bond-forming process was generated via C–N bond cleavage of aminal under base-free conditions. Moderate yields of desired amination products can be obtained under mild conditions when air was served as oxidant and PhCO2H was used as an additive.

Mechanistic studies of Wacker-type intramolecular aerobic oxidative amination of alkenes catalyzed by Pd(OAc)2/pyridine.

Wacker-type oxidative cyclization reactions have been the subject of extensive research for several decades, but few systematic mechanistic studies of these reactions have been reported. The present study features experimental and DFT computational studies of Pd(OAc)(2)/pyridine-catalyzed intramolecular aerobic oxidative amination of alkenes. The data support a stepwise catalytic mechanism that consists of (1) steady-state formation of a Pd(II)-amidate-alkene chelate with release of 1 equiv of pyridine and AcOH from the catalyst center, (2) alkene insertion into a Pd-N bond, (3) reversible β-hydride elimination, (4) irreversible reductive elimination of AcOH, and (5) aerobic oxidation of palladium(0) to regenerate the active trans-Pd(OAc)(2)(py)(2) catalyst. Evidence is obtained for two energetically viable pathways for the key C-N bond-forming step, featuring a pyridine-ligated and a pyridine-dissociated Pd(II) species. Analysis of natural charges and bond lengths of the alkene-insertion transition state suggest that this reaction is best described as an intramolecular nucleophilic attack of the amidate ligand on the coordinated alkene.

Enantioselective Hydroformylation of N-Vinyl Carboxamides, Allyl Carbamates, and Allyl Ethers Using Chiral Diazaphospholane Ligands

Rhodium complexes of diazaphospholane ligands catalyze the asymmetric hydroformylation of N-vinyl carboxamides, allyl ethers, and allyl carbamates; products include 1,2- and 1,3-aminoaldehydes and 1,3-alkoxyaldehydes. Using glass pressure bottles, short reaction times (generally less than 6 h), and low catalyst loading (commonly 0.5 mol %), 20 substrates are successfully converted to chiral aldehydes with useful regioselectivity and high enantioselectivity (up to 99% ee). Chiral Roche aldehyde is obtained with 97% ee from the hydroformylation of allyl silyl ethers. Commonly difficult substrates such as 1,1- and 1,2-disubstituted alkenes undergo effective hydroformylation with 89-97% ee and complete conversion for six examples. Palladium-catalyzed aerobic oxidative amination of allyl benzyl ether followed by enantioselective hydroformylation yields the β(3)-aminoaldehyde with 74% ee.

ChemInform Abstract: Broensted Base Modulated Regioselective Pd‐Catalyzed Intramolecular Aerobic Oxidative Amination of Alkenes: Formation of Seven‐Membered Amides and Evidence for Allylic C—H Activation.

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Intermolecular Oxidative Amination of Olefins with Amines Catalyzed by the Pd(II)/NPMoV/O2 System

A novel and efficient intermolecular aerobic oxidative amination of electron-deficient olefins with secondary aromatic amines has been successfully achieved by a Pd(II)/NPMoV/HQ-catalyzed reaction under dioxygen.

Palladium‐Catalyzed Intermolecular Aerobic Oxidative Amination of Terminal Alkenes: Efficient Synthesis of Linear Allylamine Derivatives

Palladium‐Catalyzed Intermolecular Aerobic Oxidative Amination of Terminal Alkenes: Efficient Synthesis of Linear Allylamine Derivatives

Palladium-Catalyzed Oxidative Amination of Alkenes: Improved Catalyst Reoxidation Enables the Use of Alkene as the Limiting Reagent

Palladium-catalyzed methods for intermolecular aerobic oxidative amination of alkenes have been identified that are compatible with the use of alkene as the limiting reagent. These procedures, which enhance the utility of this reaction with alkenes that are not commercially available, are demonstrated with substrates bearing dialkyl ether, carboxyester, epoxide, and silyl ether groups.

Palladium-Catalyzed Aerobic Oxidative Amination of Alkenes: Development of Intra- and Intermolecular Aza-Wacker Reactions

Palladium-catalyzed methods for the aerobic oxidative coupling of alkenes and oxygen nucleophiles (e.g., water and carboxylic acids) have been known for nearly 50 years. The present account summarizes our development of analogous aerobic oxidative amination reactions, including the first intermolecular aza-Wacker reactions compatible with the use of unactivated alkenes. The reactions are initiated by intra- or intermolecular aminopalladation of the alkene. The resulting alkylpalladium(II) intermediate generally undergoes beta-hydride elimination to produce enamides or allylic amide products, but in certain cases, the Pd-C bond can be trapped to achieve 1,2-difunctionalization of the alkene, including carboamination and aminoacetoxylation. Mechanistic studies have provided a variety of fundamental insights into the reactions, including the effect of ancillary ligands on palladium catalysts, the origin of the Brønsted-base-induced switch in regioselectivity in the oxidative amination of styrene, and evidence that both cis- and trans-aminopalladations of alkenes are possible. Overall, these reactions highlight the potential utility of an "organometallic oxidase" strategy for the selective aerobic oxidation of organic molecules.

Brønsted Base-Modulated Regioselectivity in the Aerobic Oxidative Amination of Styrene Catalyzed by Palladium

Palladium(II)-catalyzed aerobic oxidative amination of styrene with oxazolidinone proceeds with catalyst-controlled regioselectivity: (CH3CN)2PdCl2 (1) and (Et3N)2PdCl2 (2) catalyze formation of the anti-Markovnikov and Markovnikov enecarbamate products, 3 and 4, respectively. Kinetic studies and deuterium kinetic isotope effects demonstrate that these two reactions possess different rate-limiting steps, and the data indicate that the product regiochemistry arises from the presence or absence of an effective Brønsted base in the reaction. In the presence of a Brønsted base such as triethylamine or acetate, the kinetically preferred Markovnikov aminopalladation adduct of styrene is trapped via rapid deprotonation of a zwitterionic intermediate and leads to formation of 4. In the absence of an effective Brønsted base, however, slow deprotonation of this adduct enables aminopalladation to be reversible, and product formation proceeds through the thermodynamically preferred anti-Markovnikov aminopalladation adduct to yield 3.

Aerobic Oxidative Amination of Unactivated Alkenes Catalyzed by Palladium.

The first examples of palladium-catalyzed oxidative amination of unactivated alkyl olefins have been identified. To be successful, these reactions must be conducted under cocatalyst-free conditions that involve direct dioxygen-coupled turnover of the palladium catalyst. The oxidative amination products of norbornene and other cyclic alkenes implicate a cis-aminopalladation mechanism.

Aerobic Oxidative Amination of Unactivated Alkenes Catalyzed by Palladium

The first examples of palladium-catalyzed oxidative amination of unactivated alkyl olefins have been identified. To be successful, these reactions must be conducted under cocatalyst-free conditions that involve direct dioxygen-coupled turnover of the palladium catalyst. The oxidative amination products of norbornene and other cyclic alkenes implicate a cis-aminopalladation mechanism.