Copper-Catalyzed Oxidative Amidation of Aldehydes with Amine Salts: Synthesis of Primary, Secondary, and Tertiary Amides

One-Pot Oxidative Amidation of Aldehydes via the Generation of Nitrile Imine Intermediates

A one-pot procedure for the oxidative amidation of aldehydes via the in situ generation of reactive nitrile imine (NI) intermediates has been developed. Distinct from our progenitor processes, mechanistic and control experiments revealed that the NI undergoes rapid oxidation to an acyl diazene species, which then facilitates N-acylation of an amine. A range of substrates have been explored, including application in the synthesis of pharmaceutically relevant compounds.

The synthesis of alk-2-ynl Weinreb amides via Pd/Cu-catalysed oxidative carbonylation of terminal alkynes

Synthesis of alk-2-ynl-Weinreb amides via Pd-catalyzed oxidative carbonylation of terminal alkynes and N,O-dimethylhydroxylamine hydrochloride at room temperature under low CO/O2 pressure is reported for the first time. This protocol offers tolerance of various functional groups under mild reaction conditions. The protocol incorporates aromatic- and aliphatic-substituted alkynes through a one-step oxidative carbonylative route toward desired alkynyl Weinreb amides, which are of considerable importance as valuable synthetic building blocks.

Microwave Assisted Fast Synthesis of a Donor-Acceptor COF Towards Photooxidative Amidation Catalysis

The synthesis of covalent organic frameworks (COFs) at bulk scale require robust, straightforward, and cost-effective techniques. However, the traditional solvothermal synthetic methods of COFs suffer low scalability as well as requirement of sensitive reaction environment and multiday reaction time (2-10 days) which greatly restricts their practical application. Here, we report microwave assisted rapid and optimized synthesis of a donor-acceptor (D-A) based highly crystalline COF, TzPm-COF in second (10 sec) to minute (10 min) time scale. With increasing the reaction time from seconds to minutes crystallinity, porosity and morphological changes are observed for TzPm-COF. Owing to visible range light absorption, suitable band alignment, and low exciton binding energy (Eb=64.6 meV), TzPm-COF can efficaciously produce superoxide radical anion (O2⋅-) after activating molecular oxygen (O2) which eventually drives aerobic photooxidative amidation reaction with high recyclability. This photocatalytic approach works well with a variety of substituted aromatic aldehydes having electron-withdrawing or donating groups and cyclic, acyclic, primary or secondary amines with moderate to high yield. Furthermore, catalytic mechanism was established by monitoring the real-time reaction progress through in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study.

Nanophotosensitizing through Space Charge Transfer Assemblies of Pentacenequinone Derivative for 'Metal-free' Photoamidation Reactions

The present study demonstrates the influence of small portion (20 %) of organic co-solvent (DMSO/THF/ACN/MeOH) in mixed aqueous media (80 % water) in controlling the size, quantum yield and life time of the through space charge transfer assemblies (TSCT) of pentacenequinone derivative (TPy-PCQ-TPy). Among various solvent systems [H2 O : DMSO (8 : 2), H2 O : THF (8 : 2), H2 O : ACN (8 : 2) and H2 O : MeOH (8 : 2)] examined, highly emissive (Φf =12 %) and nano-sized assemblies having long life time (3.11 ns) were formed in H2 O : DMSO (8 : 2) solvent system. The solvent dependent differences in the size and excited state properties of TPy-PCQ-TPy assemblies are reflected in their photosensitizing behaviour in different solvent systems. Backed by excellent photosensitizing properties, TPy-PCQ-TPy assemblies smoothly catalyse the photoamidation reactions between unactivated/activated aldehydes and secondary amine under mild reaction conditions (visible light irradiation, aerial atmosphere, room temperature) in H2 O : DMSO (8 : 2) solvent mixture. The as prepared assemblies of TPy-PCQ-TPy also exhibit high potential to catalyse the oxidation of benzyl alcohols to aromatic aldehydes, thus, generating a possibility to use aromatic alcohols as the starting material in photoamidation reactions. The real time application of TSCT assemblies has also been demonstrated in gram scale transformation of aromatic aldehydes to aromatic amides and photooxidation of benzyl alcohol to aromatic aldehyde.

In vitro and in vivo degradation correlations for polyurethane foams with tunable degradation rates

Polyurethane foams present a tunable biomaterial platform with potential for use in a range of regenerative medicine applications. Achieving a balance between scaffold degradation rates and tissue ingrowth is vital for successful wound healing, and significant in vivo testing is required to understand these processes. Vigorous in vitro testing can minimize the number of animals that are required to gather reliable data; however, it is difficult to accurately select in vitro degradation conditions that can effectively mimic in vivo results. To that end, we performed a comprehensive in vitro assessment of the degradation of porous shape memory polyurethane foams with tunable degradation rates using varying concentrations of hydrogen peroxide to identify the medium that closely mimics measured in vivo degradation rates. Material degradation was studied over 12 weeks in vitro in 1%, 2%, or 3% hydrogen peroxide and in vivo in subcutaneous pockets in Sprague Dawley rats. We found that the in vitro degradation conditions that best predicted in vivo degradation rates varied based on the number of mechanisms by which the polymer degraded and the polymer hydrophilicity. Namely, more hydrophilic materials that degrade by both hydrolysis and oxidation require lower concentrations of hydrogen peroxide (1%) to mimic in vivo rates, while more hydrophobic scaffolds that degrade by oxidation alone require higher concentrations of hydrogen peroxide (3%) to model in vivo degradation. This information can be used to rationally select in vitro degradation conditions that accurately identify in vivo degradation rates prior to characterization in an animal model.

Polymeric copper(ii) and dimeric oxovanadium(v) complexes of amide-imine conjugate: bilirubin recognition and green catalysis

An exceptionally simple amide-imine conjugate, (E)-N'-(4-(diethylamino)-2-hydroxybenzylidene)-4-methylbenzohydrazide (L), derived by the condensation of 4-methyl-benzoic acid hydrazide (PTA) with 4-(diethylamino)-2-hydroxybenzaldehyde was utilized to prepare a dimeric oxo-vanadium (V1) and a one-dimensional (1D) copper(ii) coordination polymer (C1). The structures of L, V1 and C1 were confirmed by single crystal X-ray diffraction analysis. The experimental results indicate that V1 is a promising green catalyst for the oxidation of sulfide, whereas C1 has potential for a C-S cross-coupling reaction in a greener way. Most importantly, C1 is an efficient 'turn-on' fluorescence sensor for bilirubin that functions via a ligand displacement approach. The displacement equilibrium constant is 7.78 × 105 M-1. The detection limit for bilirubin is 1.15 nM in aqueous chloroform (chloroform/water, 1/4, v/v, PBS buffer, and pH 8.0).

Cyclotrimetaphosphate-assisted ruthenium catalyst for the hydration of nitriles and oxidation of primary amines to amides under aerobic conditions in water

Amide bonds are ubiquitous and regarded as an essential constituent of many biologically active drug molecules and fine chemicals. We report a practical and operationally simple ruthenium-based catalytic system for the hydration of nitriles and aerobic oxidation of primary amines to the corresponding amides. Both reactions proceed without any external oxidant in water under aerobic conditions and exhibit a broad substrate scope. The mechanistic investigation was executed with the aid of control experiments and kinetic and spectroscopic studies of the reaction mixture.

Solvent-controlled amidation of acid chlorides at room temperature: new route to access aromatic primary amides and imides amenable for late-stage functionalization†

Herein, we report a solvent-controlled highly selective amidation and imidation of aroyl chlorides using an alkali-metal silyl-amide reagent (LiHMDS), which serves as a nitrogen source at room temperature. A unique feature of this method lies in the sequential silyl amidation of aryol chlorides and nitrogen–silicon bond cleavage of the corresponding N,N-bis(trimethylsilyl)benzamide in a one-pot method in a very short reaction time. This effective strategy was extended to late-stage functionalization.

Herein, we report a solvent-controlled highly selective amidation and imidation of aroyl chlorides using an alkali-metal silyl-amide reagent (LiHMDS), which serves as a nitrogen source at room temperature.

Transamidation of aromatic amines with formamides using cyclic dihydrogen tetrametaphosphate

Amide fragments are found to be one of the key constituents in a wide range of natural products and pharmacologically active compounds. Herein, we report a simple and efficient procedure for transamidation with a cyclic dihydrogen tetrametaphosphate. The protocol is simple, does not require any additives, and encompasses a broad substrate scope. To comprehend the mechanism of the present methodology, detailed spectroscopic and kinetic studies were undertaken.

Synthesis and characterization of rare earth/lithium complexes stabilized by ethylenediamine-bridged bis(phenolate) ligands and their activity in catalyzing amidation reactions

Rare earth/lithium complexes stabilized by ethylenediamine-bridged bis(phenolate) ligands have been synthesized and characterized. In addition to five rare earth/lithium amides isolated as major complexes, two other rare earth/lithium complexes bearing two phenolate ligands were also isolated. The activities of rare earth/lithium amides in catalyzing the amidation of aldehydes and amines were studied, which revealed that the yttrium/lithium complex was highly active for a wide range of substrates, generating 58 examples of amides in 42-99% yields under mild conditions (i.e., room temperature, 3-hour reaction time, additive-free). More importantly, this is the first example of rare earth-based catalysts capable of catalyzing the amidation of primary aliphatic amines.

Acceptorless dehydrogenative synthesis of primary amides from alcohols and ammonia

The highly desirable synthesis of the widely-used primary amides directly from alcohols and ammonia via acceptorless dehydrogenative coupling represents a clean, atom-economical, sustainable process. Nevertheless, such a reaction has not been previously reported, and the existing catalytic systems instead generate other N-containing products, e.g., amines, imines and nitriles. Herein, we demonstrate an efficient and selective ruthenium-catalyzed synthesis of primary amides from alcohols and ammonia gas, accompanied by H₂ liberation. Various aliphatic and aromatic primary amides were synthesized in high yields, with no observable N-containing byproducts. The selectivity of this system toward primary amide formation is rationalized through density functional theory (DFT) calculations, which show that dehydrogenation of the hemiaminal intermediate into primary amide is energetically favored over its dehydration into imine.

An efficient and selective synthesis of primary amides from alcohols and ammonia, with H₂ evolution, has been achieved by an unprecedented acceptorless dehydrogenative process catalyzed by a pyridine-based PNN–ruthenium pincer complex.

Diamine-functionalized porous graphene oxide sheets decorated with palladium oxide nanoparticles for the oxidative amidation of aldehydes

C–N coupling between aldehydes and amines by ultra-small PdO NPs adorned diamine functionalized porous GO sheets as retrievable nano-catalyst.

Amide Bond Formation via the Rearrangement of Nitrile Imines Derived from N-2-Nitrophenyl Hydrazonyl Bromides

We report how the rearrangement of highly reactive nitrile imines derived from N-2-nitrophenyl hydrazonyl bromides can be harnessed for the facile construction of amide bonds. This amidation reaction was found to be widely applicable to the synthesis of primary, secondary, and tertiary amides and was used as the key step in the synthesis of the lipid-lowering agent bezafibrate. The orthogonality and functional group tolerance of this approach was exemplified by the N-acylation of unprotected amino acids.

Pd-Catalyzed Oxidative Aminocarbonylation of Arylboronic Acids with Unreactive Tertiary Amines via C-N Bond Activation

An efficient synthesis of tertiary amides from aryl boronic acids and inert tertiary amines through the oxidative carbonylation via C(sp³)-N bond activation is presented. This protocol significantly restricts the homocoupling biarylketone product. It involves the use of a homogeneous PdCl₂/CuI catalyst and a heterogeneous Pd/C based catalyst, which promotes C(sp³)-N bond activation of tertiary amines with aryl boronic acids. This process represents a ligand-free, base-free, and recyclable catalyst along with an ideal oxidant like molecular oxygen.

Direct synthesis of amides and imines by dehydrogenative homo or cross-coupling of amines and alcohols catalyzed by Cu-MOF

Oxidative dehydrogenative homo-coupling of amines to imines and cross-coupling of amines with alcohols to amides was achieved with high to moderate yields at room temperature in THF using Cu-MOF as an efficient and recyclable heterogeneous catalyst under mild conditions. Different primary benzyl amines and alcohols could be utilized for the synthesis of a wide variety of amides and imines. The Cu-MOF catalyst could be recycled and reused four times without loss of catalytic activity.

Photochemical Activation of Aromatic Aldehydes: Synthesis of Amides, Hydroxamic Acids and Esters

A cheap, facile and metal-free photochemical protocol for the activation of aromatic aldehydes has been developed. Utilizing thioxanthen-9-one as the photocatalyst and cheap household lamps as the light source, a variety of aromatic aldehydes have been activated and subsequently converted in a one-pot reaction into amides, hydroxamic acids and esters in good to high yields. The applicability of this method was highlighted in the synthesis of Moclobemide, a drug against depression and social anxiety. Extended and detailed mechanistic studies have been conducted, in order to determine a plausible mechanism for the reaction.

Asymmetric copper-catalyzed propargylic amination with amine hydrochloride salts

The highly enantioselective copper-catalyzed propargylic amination of propargylic esters with amine hydrochloride salts has been realized for the first time using copper salts with chiral N,N,P-ligands. This method features a broad substrate scope and wide functional group tolerance, generating propargylic amines in good to excellent yields with high enantioselectivities (up to 99% ee). The utility of the approach was demonstrated by late-stage functionalization of marketed pharmaceuticals.

Visible-Light-Mediated Oxidative Amidation of Aldehydes by Using Magnetic CdS Quantum Dots as a Photocatalyst

A magnetic CdS quantum dot (Fe₃ O₄ /polydopamine (PDA)/CdS) was synthesized through a facile and convenient method from inexpensive starting materials. Characterization of the prepared catalyst was performed by means of FTIR spectroscopy, XRD, SEM, TEM, energy-dispersive X-ray spectroscopy, and vibrating-sample magnetometer techniques. Fe₃ O₄ /PDA/CdS was found to be a highly active photocatalyst for the amidation of aromatic aldehydes by using air as a clean oxidant under mild conditions. The photocatalyst can be recovered by magnetic separation and successfully reused for five cycles without considerable loss of its catalytic activity.

Ring Opening/Site Selective Cleavage in N-Acyl Glutarimide to Synthesize Primary Amides

A LiOH-promoted hydrolysis selective C-N cleavage of twisted N-acyl glutarimide for the synthesis of primary amides under mild conditions has been developed. The reaction is triggered by a ring opening of glutarimide followed by C-N cleavage to afford primary amides using 2 equiv of LiOH as the base at room temperature. The efficacy of the reactions was considered and administrated for various aryl and alkyl substituents in good yield with high selectivity. Moreover, gram-scale synthesis of primary amides using a continuous flow method was achieved. It is noted that our new methodology can apply under both batch and flow conditions for synthetic and industrial applications.

Selective Utilization of N-acetyl Groups in Chitin for Transamidation of Amines

The selective transformation of chitin into various renewable N-containing chemicals and medicines has attracted increasing attention. However, the N-acetyl groups in chitin construct strong hydrogen bond networks, which restricts its depolymerization and transformation. The selective conversion of robust chitin commonly requires considerable base catalysts to remove the N-acetyl group as a byproduct in advance, which is non-compliance with the principle of atomic economy. Herein, for the first time we demonstrate a novel approach to achieve the selective utilization of the N-acetyl group in chitin for transamidation of chitin with amines. A series of amine derivatives, mainly including aliphatic amine, cyclic amine and functionalized aromatic amine, could be selectively converted into the corresponding amide products frequently found in pharmaceuticals. Furthermore, the solid residue after removing the acetyl group (denoted as De-chitin) with the sufficient exposure of -NH2 groups as a solid base catalyst shows excellent performance in the aldol condensation reaction of furfural and acetone to produce fuel precursors. Our process provides a strategy that exploiting every functional group adequately in substrates to obtain value-added chemicals.

Aerobic oxidation of primary amines to amides catalyzed by an annulated mesoionic carbene (MIC) stabilized Ru complex

A Ru complex, stabilized by an annulated mesoionic carbene ligand, catalyzes the aerobic oxidation of a host of primary amines to amides in high yields and excellent selectivity. Kinetics, Hammett and DFT studies provide mechanistic insight.

Cu-catalyzed cross-coupling of methyl ketones and pyridin-2-amines for the synthesis of N-(2-pyridyl)-α-ketoamides

An efficient copper-catalyzed strategy for the synthesis of α-ketoamides via cross-coupling of methyl ketones and pyridin-2-amines is described. This transformation has provided a simple process for the formation of C−N and C=O bonds to prepare α-ketoamides, which are important substrates and intermediates for the preparation of fine chemicals. The reaction mechanism is investigated, which suggests that the reaction proceeds via a radical pathway.

Amide Synthesis through the In Situ Generation of Chloro- and Imido-Phosphonium Salts

We describe a methodology for the amidation of carboxylic acids by generating phosphonium salts in situ from N-chlorophthalimide and triphenylphosphine. Aliphatic, benzylic, and aromatic carboxylic acids can be transformed into their amide counter parts using primary and secondary amines. This functional group interconversion is achieved at room temperature in good to excellent yields. Mechanistic work shows the in situ formation of chloro- and imido-phosphonium salts that react as activating agents for carboxylic acids and generate an acyloxy-phosphonium species.

Pyridine-Enabled C-N Bond Activation for the Rapid Construction of Amides and 4-Pyridylglyoxamides by Cooperative Palladium/Copper Catalysis

A pyridine-enabled C-N bond activation of peptidomimetics employing cooperative palladium/copper catalysis in water is developed. Diverse amides and 4-pyridylglyoxamides are simultaneously synthesized through two steps from commercially available materials in a rapid, environmentally friendly, and high atom-economical manner.

Direct synthesis of amides from nonactivated carboxylic acids using urea as nitrogen source and Mg(NO3)2 or imidazole as catalysts

A new method for the direct synthesis of primary and secondary amides from carboxylic acids is described using Mg(NO3)2·6H2O or imidazole as a low-cost and readily available catalyst, and urea as a stable, and easy to manipulate nitrogen source. This methodology is particularly useful for the direct synthesis of primary and methyl amides avoiding the use of ammonia and methylamine gas which can be tedious to manipulate. Furthermore, the transformation does not require the employment of coupling or activating agents which are commonly required.

Oxidative amidation by Cu(ii)–guanidine acetic acid immobilized on magnetized sawdust with eggshell as a natural base

Copper(ii)–guanidine acetic acid complex was immobilized on the surface of magnetized raw waste sawdust (SD) as an abundant natural biopolymer and employed as an efficient and recoverable catalyst in oxidative amidation reaction, while waste eggshell (ES) powder was used as a low-cost solid base.

Graphene oxide: a convenient metal-free carbocatalyst for facilitating amidation of esters with amines

Herein, we have reported a graphene oxide (GO) catalyzed condensation of non-activated esters and amines, that can enable diverse amides to be synthesized from abundant ethyl esters forming only volatile alcohol as a by-product.

Visible-Light-Enabled Aminocarbonylation of Unactivated Alkyl Iodides with Stoichiometric Carbon Monoxide for Application on Late-Stage Carbon Isotope Labeling

A visible-light-mediated late-stage aminocarbonylation of unactivated alkyl iodides with stoichiometric amounts of carbon monoxide is presented. The method provides a mild, one-step route to [carbonyl-^13/14C] alkyl amides, thereby reducing radioactive waste, and handling of radioactive materials. Easily accessible and low-cost equipment and a palladium catalyst were successfully used for the synthesis of a wide range of alkyl amides.

(Ar-tpy)RuII(ACN)3: A Water-Soluble Catalyst for Aldehyde Amidation, Olefin Oxo-Scissoring, and Alkyne Oxygenation

The synthetic chemists always look for developing new catalysts, sustainable catalysis, and their applications in various organic transformations. Herein, we report a new class of water-soluble complexes, (Ar-tpy)Ru^II(ACN)₃, utilizing designed terpyridines possessing electron-donating and -withdrawing aromatic residues for tuning the catalytic activity of the Ru(II) complex. These complexes displayed excellent catalytic activity for several oxidative organic transformations including late-stage C-H functionalization of aldehydes with NH₂OR to valuable primary amides in nonconventional aqueous media with excellent yield. Its diverse catalytic power was established for direct oxo-scissoring of a wide range of alkenes to furnish aldehydes and/or ketones in high yield using a low catalyst loading in the water. Its smart catalytic activity under mild conditions was validated for dioxygenation of alkynes to highly demanding labile synthons, 1,2-diketones, and/or acids. This general and sustainable catalysis was successfully employed on sugar-based substrates to obtain the chiral amides, aldehydes, and labile 1,2-diketones. The catalyst is recovered and reused with a moderate turnover. The proposed mechanistic pathway is supported by isolation of the intermediates and their characterization. This multifaceted sustainable catalysis is a unique tool, especially for late-stage functionalization, to furnish the targeted compounds through frequently used amidation and oxygenation processes in the academia and industry.