One-pot synthesis of amides via the oxidative amidation of aldehydes and amines catalyzed by a copper-MOF

An efficient method for the oxidative amidation of aldehydes with primary aromatic and aliphatic amines has been developed for the synthesis of a wide variety of amides using inexpensive Cu₂(BDC)₂DABCO (Cu-metal–organic framework [MOF]) as a recyclable heterogeneous catalyst, and N-chlorosuccinimide and aqueous tert-butyl hydroperoxide as oxidants in acetonitrile. This amidation reaction is operationally straightforward and provides secondary amides in good yields in most cases, utilizing inexpensive and readily available reagents under mild conditions.

A method for oxidative amidation of aldehydes with primary amines was developed to synthesise a variety of amides using Cu₂(BDC)₂DABCO (Cu-MOF) as a recyclable heterogeneous catalyst, and N-chlorosuccinimide and aqueous tert-butyl hydroperoxide as oxidants in acetonitrile.     

Uniform Cu/chitosan beads as a green and reusable catalyst for facile synthesis of imines via oxidative coupling reaction

A nonprecious metal and biopolymer-based catalyst, Cu/chitosan beads, has been successfully prepared by using a software-controlled flow system. Uniform, spherical Cu/chitosan beads can be obtained with diameters in millimeter-scale and narrow size distribution (0.78 ± 0.04 mm). The size and morphology of the Cu/chitosan beads are reproducible due to high precision of the flow rate. In addition, the application of the Cu/chitosan beads as a green and reusable catalyst has been demonstrated using a convenient and efficient protocol for the direct synthesis of imines via the oxidative self- and cross-coupling of amines (24 examples) with moderate to excellent yields. Importantly, the beads are stable and could be reused more than ten times without loss of the catalytic performance. Furthermore, because of the bead morphology, the Cu/chitosan catalyst has greatly simplified recycling and workup procedures.

Uniform, spherical Cu/chitosan beads prepared using a software-controlled flow system as a green and conveniently recyclable catalyst for the efficient synthesis of various imines in short reaction time.     

Metal- and oxidant-free electrochemically promoted oxidative coupling of amines

The selective oxidation of amines into imines is a priority research topic in organic synthesis and has attracted much attention over the past few decades. However, the oxidation of amines generally suffers from the drawback of transition-metal, even noble-metal catalysts. Thus, the strategy of metal- and oxidant-free selective synthesis of imines is highly desirable yet largely unmet. This paper unravels a metal-free and external oxidant-free electrochemical strategy for the oxidative coupling methodology of amines. This general transformation is compatible with various functional amines and led to functionalized imines in moderate to satisfactory yields.

This paper presents a metal-free and external oxidant-free electrochemical method for the oxidative coupling methodology of amines in moderate to satisfactory yields.     

Tandem imine formation via auto-hydrogen transfer from alcohols to nitro compounds catalyzed by a nanomagnetically recyclable copper catalyst under solvent-free conditions

A direct imination reaction was developed by tandem reaction of alcohols and nitro compounds in the presence of Cu-isatin Schiff base-γ-Fe₂O₃ as a nanomagnetically recyclable catalyst under solvent-free conditions. By this method, various imines were prepared in good to high yields from one-pot reaction of various alcohols (primary aromatic and aliphatic) and nitro compounds (aromatic and aliphatic) via an auto-hydrogen transfer reaction. Use of an inexpensive and easily reusable catalyst, without requiring any additives or excess amounts of benzyl alcohol as the reaction solvent are the other advantages of this method. This catalytic system has the merits of cost effectiveness, environmental benignity, excellent recyclability and good reproducibility.

A direct imination reaction was developed by tandem reaction of alcohols and nitro compounds in the presence of Cu-isatin Schiff base-γ-Fe₂O₃ as a nanomagnetically recyclable catalyst.     

Ni/Pd-catalyzed Suzuki–Miyaura cross-coupling of alcohols and aldehydes and C–N cross-coupling of nitro and amines via domino redox reactions: base-free,hydride acceptor-free

Domino oxidation-Suzuki–Miyaura cross-coupling of benzyl alcohols with phenylboronic acid and domino reduction-C–N cross-coupling of the nitro compounds with aryl halides were carried out using a strong Ni/Pd bimetallic redox catalyst. The catalyst bearing a copolymer with two Ni/Pd coordinated metals in porphyrin (derived from demetalated chlorophyll b) and salen-type ligands, and pyridine moiety as a base functionality all immobilized on magnetite NPs was synthesised and characterized. The domino oxidation cross-coupling reaction was accomplished under molecular O₂ in the absence of any hydride acceptor or/and base. Also, the domino reduction C–N cross-coupling reaction was performed in the presence of NaBH₄ without the need for any base and co-reductant. This multifunctional catalyst gave moderate to good yields for both coupling reactions with high chemoselectivity. A wide investigation was conducted to determine its mechanism and chemoselectivity.

A new Ni/Pd bimetallic multifunctional catalytic system has been developed for the domino Suzuki–Miyaura cross-coupling of benzyl alcohols with phenyl boronic acid and domino reduction C–N cross-coupling of the nitro compounds with aryl halides.     

Innovative application of magnetically modified bovine horn as a natural keratin resource in the role of value-added organocatalyst

This study presents the conversion of bovine horn powder (BHP) as an available and low-cost waste material to a value-added highly recyclable catalyst. This green catalyst was prepared through the immobilization of BHP, as a natural keratin resource, on the magnetic Fe₃O₄ nanoparticles. The successful preparation of the catalyst was fully investigated using Fourier transform infrared, X-ray diffraction, and energy-dispersive X-ray spectroscopies as well as field emission scanning electron microscopy, vibrating sample magnetometry, and thermogravimetry. The catalytic efficiency of the prepared magnetic organocatalyst was evaluated in the synthesis of a large series of amide derivatives through the solvent-free transamidation reaction of different amides and amines with yields of 75–96%.

The conversion of bovine horn powder as an available and low-cost waste material to a value-added recyclable organocatalyst for transamidation reaction.     

Cu-catalyzed cross-coupling reactions of vinyl epoxide with organoboron compounds: access to homoallylic alcohols

Copper-catalyzed cross-coupling reactions of vinyl epoxide with arylboronates to obtain aryl-substituted homoallylic alcohols are described. The reaction selectivity was different to that of previously reported vinyl epoxide ring-opening reactions using aryl nucleophiles. The reaction proceeded under mild conditions, affording aryl-substituted homoallylic alcohols with high selectivity and in good to excellent yields. The reaction provides convenient access to aryl-substituted homoallylic alcohols from vinyl epoxide

Copper-catalyzed cross-coupling reactions of vinyl epoxide with arylboronates to obtain aryl-substituted homoallylic alcohols are described.     

Lithium bromide: an inexpensive and efficient catalyst for imine hydroboration with pinacolborane at room temperature

An efficient protocol for the hydroboration of imines is reported. Lithium halide salts are effective catalysts to convert aldimines and ketimines to their corresponding amines. Here, we report excellent isolated yield of secondary amines (>95%) using 3 mol% lithium bromide in THF at room temperature. In addition, DFT calculations for a plausible reaction pathway are reported.

An efficient protocol for the hydroboration of imines using LiBr is reported.     

Cu-metal organic frameworks (Cu-MOF) as an environment-friendly and economical catalyst for one pot synthesis of tacrine derivatives

The present work describes the catalytic activity of Cu-MOF for the one-pot synthesis of tacrine derivatives via a four-component reaction of 2-hydroxynaphthalene-1,4-dione, aldehydes, malononitrile and cycloketones in the presence of AlCl₃. The structure of the synthesized compound is confirmed by ¹H NMR, ¹³C NMR, IR, and MASS. The catalyst prepared under pressure is characterized by powder X-ray diffraction and SEM. The noteworthy advantages of this procedure include its broad substrate scope, high yields up to 93%, atom economy, using readily available starting materials and a powerful recyclable nano catalyst. Additionally, there is no need to use column chromatography for purifying products so, it has the potential for large-scale applications in pharmaceutical industries. Another advantage of this method is the ability to recycle the catalyst up to 3 times and reuse it.

The present work describes the catalytic activity of Cu-MOF for the one-pot synthesis of tacrine derivatives via a four-component reaction of 2-hydroxynaphthalene-1,4-dione, aldehydes, malononitrile and cycloketones in the presence of AlCl₃.     

Oxidative amidation of benzaldehyde using a quinone/DMSO system as the oxidizing agent

An efficient transition-metal-based heterogeneous catalyst free procedure for obtaining the oxidative amidation of benzaldehyde using quinones as oxidizing agents in low molar proportions is described here. Pyrrolylquinones (PQ) proved to be more suitable than DDQ and 2,5-dimethylbenzoquinone to conduct the oxidation process. Although the solvent itself acted as the oxidant with low to moderate yields, PQ/DMSO provided an efficient system for carrying out the reaction under operational simplicity, mild reaction conditions, short reaction times and high yields of the desired product. The scope of the method was evaluated with substituted benzaldehydes and secondary amines. Theoretical foundations are given to explain the participation of quinones as an oxidizing agent in the reaction.

An efficient transition-metal-based heterogeneous catalyst free procedure for obtaining the oxidative amidation of benzaldehyde using quinones as oxidizing agents in low molar proportions is described here.     

Visible-light enabled room-temperature dealkylative imidation of secondary and tertiary amines promoted by aerobic ruthenium catalysis

Employing sulfonyl azide as a nitrogen donor, a visible-light-enabled aerobic dealkylative imidation of tertiary and secondary amines involving C(sp³)–C(sp³) bond cleavage with moderate to excellent yields at room temperature is described. It has been demonstrated that this imidation could take place spontaneously upon visible-light irradiation, and could be facilitated considerably by a ruthenium photocatalyst and oxygen. An alternative mechanism to the previous aerobic photoredox pathway has also been proposed.

A photoredox dealkylative imidation of tertiary and secondary amines with sulfonyl azide facilitated by aerobic ruthenium-catalysis to afford sulfonyl amidine at room temperature is reported.     

TiO2 nanoparticles decorated with Co-Schiff base-g-C3N4 as an efficient photocatalyst for one-pot visible light-assisted synthesis of benzimidazoles

In this study, a novel heterogeneous visible light-driven nanocatalyst was produced via the complexation of Co(ii) with g-C₃N₄-imine-functionalized TiO₂ nanoparticles. It was characterized using different techniques such as Fourier-transform infrared (FT-IR), energy-dispersive X-ray spectrum (EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), thermogravimetric analysis (TGA), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The catalyst promoted several different transformations in a one-pot reaction sequence: aerobic photooxidation of benzylic alcohols to aldehydes and then the tandem synthesis of benzimidazoles through the dehydrogenative coupling of primary benzylic alcohols and aromatic diamines. The photocatalyst proved to be highly active, robust, selective, and recyclable under organic reaction conditions and provided affordable products with good to high yields. The results proposed that the improved photoactivity predominantly benefits from the synergistic effects of the heterojunction of Co-carbon nitride on TiO₂ nanoparticles. Moreover, this protocol provides standard conditions avoiding undesirable additives and limitations of oxidation methods, and may help to develop a new strategy for the development of photocatalysis based organic transformations.

The Co-g-C₃N₄-imine/TiO₂ nanohybrid promotes different transformations in a one-pot reaction sequence: aerobic photooxidation of benzylic alcohols to aldehydes, and then the tandem synthesis of benzimidazoles.     

Expedient approach for trans-esterification of β-keto esters under solvent free conditions using silica supported boric acid (SiO2–H3BO3) as a recyclable catalyst

A highly efficient trans-esterification of β-keto methyl/ethyl esters with primary, secondary, allylic, benzylic and chiral alcohols has been carried out in excellent yields under solvent-free conditions using silica supported boric acid as a heterogeneous catalyst. The surface morphology of the silica-boric acid catalyst (fresh and recycled) has been characterized by SEM and EDX techniques. This sustainable protocol resulted in a remarkable enhancement in the synthetic efficiency (87–95% yield) with high purity and eliminating the use of an environmentally toxic solvent. The work up procedure is very simple and the catalyst has been successfully recovered and recycled. The present methodology is also applicable for trans-esterification with chiral alcohols on a multi-gram scale without compromising the yield. Noteworthy features of this protocol are simple operational procedure, minimizing production of chemical waste, mild reaction conditions, easy preparation of the catalyst and its recyclability up to five cycles without any appreciable loss of catalytic activity.

A simple, mild, high yielding and minimizing chemical waste procedure for trans-esterification of β-keto methyl/ethyl esters with alcohol groups was developed under solvent-free condition using silica-boric acid as recyclable heterogeneous catalyst.     

An efficient and environmentally sustainable domino protocol for the synthesis of structurally diverse spiroannulated pyrimidophenazines using erbium doped TiO2 nanoparticles as a recyclable and reusable heterogeneous acid catalyst

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated pyrimidophenazines involving a four component reaction of 2-hydroxynaphthalene-1,4-dione, benzene-1,2-diamine, cyclic ketones and amino derivatives in the presence of erbium doped TiO₂ nanoparticles as a recyclable and reusable heterogeneous acid catalyst. The present synthetic protocol features mild reaction conditions with operational simplicity, excellent yield with high purity, short reaction time and high atom economy with the use of a recoverable and reusable environmentally sustainable heterogeneous catalyst.

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated pyrimidophenazines using erbium doped TiO₂ nanoparticles as a recyclable and reusable heterogeneous acid catalyst.     

Ti-superoxide catalyzed oxidative amidation of aldehydes with saccharin as nitrogen source: synthesis of primary amides

A new heterogeneous catalytic system (Ti-superoxide/saccharin/TBHP) has been developed that efficiently catalyzes oxidative amidation of aldehydes to produce various primary amides. The protocol employs saccharin as amine source and was found to tolerate a wide range of substrates with different functional groups. Moderate to excellent yields, catalyst reusability and operational simplicity are the main highlights. A possible mechanism and the role of the catalyst in oxidative amidation have also been discussed.

Heterogeneous catalytic system using Ti-superoxide and saccharin with TBHP has been developed which catalyzes oxidative amidation of aldehyde to produce primary amides. It tolerates a wide range of substrates with different functional groups.     

Copper-catalyzed intramolecular cross dehydrogenative coupling approach to coumestans from 2′-hydroxyl-3-arylcoumarins

A copper-catalyzed intramolecular cross dehydrogenative C–O coupling reaction of 2′-hydroxyl-3-arylcoumarins was developed. This protocol provided a facile and efficient strategy for the construction of natural coumestans and derivatives in moderate to high yields. This transformation exhibited good functional group compatibility and was amenable to substrates with free phenolic hydroxyl groups.

A copper-catalyzed intramolecular cross dehydrogenative C–O coupling reaction of 2′-hydroxyl-3-arylcoumarins was developed.     

Oxone promoted dehydrogenative Povarov cyclization of N-aryl glycine derivatives: an approach towards quinoline fused lactones and lactams

Oxone promoted intramolecular dehydrogenative imino Diels–Alder reaction (Povarov cyclization) of alkyne tethered N-aryl glycine esters and amides has been explored, thus affording biologically significant quinoline fused lactones and lactams. The reaction is simple, scalable, and high yielding (up to 88%). The method was further extended to prepare biologically important luotonin-A analogues and the quinoline core of uncialamycin.

Oxone promoted intramolecular dehydrogenative imino Diels–Alder reaction (Povarov cyclization) of alkyne tethered N-aryl glycine esters and amides has been explored, thus affording biologically significant quinoline fused lactones and lactams.     

Reduction of imines with a reusable bimetallic PdCo–Fe3O4 catalyst at room temperature under atmospheric pressure of H2

Bimetallic nanocatalysts have been used for the development of organic reactions, owing to the synergistic effect between the transition metals. A new procedure for synthesizing amines by the reduction of imines with H₂ at atmospheric pressure and room temperature in the presence of PdCo–Fe₃O₄ nanoparticles is reported. The straightforward procedure, mild reaction conditions, high turnover number, and recyclability extend the scope of this reaction to practical applications.

A catalytic procedure that has mild reaction conditions, high turnover number, and the recyclability of the catalyst is presented, whereby the synthesis of amines through the reduction of imines employing PdCo–Fe₃O₄ under atmospheric pressure of H₂ is achieved.     

A template free protocol for fabrication of a Ni(ii)-loaded magnetically separable nanoreactor scaffold for confined synthesis of unsymmetrical diaryl sulfides in water

In the present report, an environmentally benign magnetically recoverable nickel(ii)-based nanoreactor as a heterogeneous catalyst has been developed via a template free approach. The catalytic performance of the synthesized catalyst is assessed in the confined oxidative coupling of arenethiols with arylhydrazines to form unsymmetrical diaryl sulfides under aerobic conditions. The salient features of our protocol include oxidant- and ligand-free conditions, use of water as a green solvent, room temperature and formation of nitrogen and water as the only by-products. Moreover, a broad range of functional groups are tolerated well and provide the corresponding diaryl sulfides in moderate to good yields. Moreover, the heterogeneous nature of the catalyst permits facile magnetic recovery and reusability for up to seven runs, making the present protocol highly desirable from industrial and environmental standpoints.

An environmentally benign nickel(ii)-based magnetic nanoreactor has been developed for oxidative coupling of arenethiols with arylhydrazines to form unsymmetrical diaryl sulfides in water at room temperature.     

Practical one-pot amidation of N-Alloc-, N-Boc-, and N-Cbz protected amines under mild conditions

A facile one-pot synthesis of amides from N-Alloc-, N-Boc-, and N-Cbz-protected amines has been described. The reactions involve the use of isocyanate intermediates, which are generated in situ in the presence of 2-chloropyridine and trifluoromethanesulfonyl anhydride, to react with Grignard reagents to produce the corresponding amides. Using this reaction protocol, a variety of N-Alloc-, N-Boc-, and N-Cbz-protected aliphatic amines and aryl amines were efficiently converted to amides with high yields. This method is highly effective for the synthesis of amides and offers a promising approach for facile amidation.

One-pot efficient transformation of N-Alloc-, N-Boc-, and N-Cbz protected amines to amides was achieved by using 2-chloropyridine and trifluoromethanesulfonyl anhydride as well as Grignard reagent and MgCl₂.