Neat Conditions Research Articles

Ionic liquid catalysed aerobic oxidative amidation and thioamidation of benzylic amines under neat conditions

Tetrabutylammonium hydroxide catalysed oxidative amidation and thioamidation of benzylamines with oxygen and elemental sulfur under solvent/metal/base-free conditions have been developed.

I2-catalyzed intramolecular oxidative amination of C(sp3)-H bond: efficient access to 3-acylimidazo[1,2-a]pyridines under neat condition.

An efficient and “green” protocol for the synthesis of 3-acylimidazo[1,2-a]pyridines through intramolecular oxidative α-amination of carbonyl compounds has been developed. The reaction proceeds smoothly utilizing I2 as a catalyst and H2O2 as an oxidant under neat condition with broad substrate scope. Several complex nitrogen-containing fused rings are conveniently constructed, which are not easy to access by traditional methods.

A catalyst- and solvent-free protocol for the sustainable synthesis of fused 4H-pyran derivatives.

An efficient and cost-effective method was developed for the synthesis of two kinds of fused 4H-pyran derivatives, namely, dihydropyrano[2,3-c]pyrazole 4 and pyrano[3,2-c]chromenone 6. The reactions of 3-methyl-1-phenyl-5-pyrazolone/4-hydroxycoumarin with aromatic aldehydes and (E)-N-methyl-1-(methylthio)-2-nitroethenamine (NMSM), involving the Knoevenagel, Michael-addition, O-cyclization and elimination reactions under thermal heating, afforded the desired products. The synthesized compounds were characterized by standard spectroscopic techniques. Further, the structures of pyrazole-fused 4H-pyran 4a and coumarin-fused 4H-pyran 6b were confirmed by single-crystal XRD analysis. The short reaction time, good-to-excellent yields, elimination of the use of expensive, metallic and toxic catalysts or hazardous organic solvents and high atom-economy are some noteworthy features of this protocol.

Base mediated green synthesis of enantiopure 2-C-spiro-glycosyl-3-nitrochromenes.

A novel green synthetic methodology has been developed to obtain enantiopure (2S)-2-C-spiro-glycosyl-3-nitrochromenes following the oxa-Michael-aldol condensation reaction of sugar derived 3-C-vinyl nitro olefins with substituted salicylaldehydes using Et3N as a base under neat conditions at rt-40 °C. The stereochemistry of the product is confirmed by a single crystal X-ray study. Several advantages are associated with this protocol such as cost effectiveness, easy accessibility, short reaction time, high yields, wide substrate scope and high enantiopurity.

Fixing CO2 into β-oxopropylcarbamates in neat condition by ionic gelation/Ag(i) supported on dendritic fibrous nanosilica.

In this research, a novel approach to produce a novel nanocatalyst, AgBr supported on an ionic gelation (IG)-based nanomaterial, was developed through the aqueous coprecipitation approach for the dendritic fibrous nanosilica (DFNS) production and the wet impregnation method for IG coating, taking into account TPP as the cross-linking agent. In addition, DFNS/IG@Ag(i) had heterogeneous features that contributed to the quick improvement of the catalyst by filtration separation. The catalytic activity of DFNS/IG@Ag(i) was examined to synthesize β-oxopropylcarbamates through a multicomponent coupling of CO2, amines and propargyl alcohols in moderate conditions. The DFNS/IG@Ag(i) NPs were completely investigated by taking advantage of TG, TEM, FESEM and FT-IR spectroscopy analyses. The DFNS/IG@Ag(i) nanocatalyst indicated high stability in the reaction for five cycles without considerable loss of some properties like activity, which could be because of the high loading of IG on the catalyst surface.

Hydration of Alkynes Catalyzed by L–Au–X under Solvent- and Acid-Free Conditions: New Insights into an Efficient, General, and Green Methodology

L–Au–X [L = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene {NHCiPr}, tris(3,5-bis(trifluoromethyl)phenyl)phosphine {PArF}, bis(imino)acenaphtene-1,3-bis(2,6-di-isopropylphenyl)dihydroimidazol-2-ylidene {BIAN}, 1,3-bis(2,6-di-isopropyl-phenyl)dihydroimidazol-2-ylidene {NHCCH2}, bis(tert-butylamino)methylidene {NAC}, 2-(di-tert-butylphosphino)biphenyl {JohnPhos}, tricyclohexylphosphine {PCy3}, triphenylphosphine {PPh3}, tris(2,4-di-tert-butylphenyl)phosphite {POR3}; X– = Cl–, OTf–, OTs–] catalysts were tested in the hydration of alkynes in neat and acid-free conditions. The overall catalytic evidence confirms that not only the counterion as previously observed by us but also the ligand play a crucial role. As a matter of fact, only complexes bearing NHC ligands showed appreciable catalytic activity. A complete rationalization of the ligand and counterion effects enabled us to develop a highly efficient methodology for the hydration of inactive diphenylacetylene in solvent-, silver-, and acid-free conditions. Thus, it was possible to reduce the catalyst loading to 0.01 mol % (with respect to diphenylacetylene) leading, to the best of our knowledge, to the highest TON (3400) and TOF (435 h–1) values found at 120 °C. The favorable catalytic conditions allowed us to reach for the first time very low E-factor (0.03) and high EMY (77) values for this substrate.

Palladium acetate-catalysed one-pot green synthesis of bis α-aminophosphonates

A simple and effective green method has been developed for the synthesis of a series of novel bis α-aminophosphonate derivatives (4a–j) by the reaction of 1,4-diaminonaphthalene, various aryl/heteroaryl aldehydes and dialkyl phosphites under neat and microwave irradiation conditions using palladium acetate as catalyst. The products are characterized by elemental analysis, IR, 1H, 13C, 31P-NMR and mass spectra and their antioxidant activities are evaluated by DPPH, NO and H2O2 methods and molecular docking studies. The compounds 4d and 4h exhibited the highest radical scavenging activity in the DPPH method, while compounds 4a, 4e and 4f showed good NO scavenging activity. The compound 4g showed remarkably higher H2O2 scavenging activity than even the standard ascorbic acid, and compound 4h has stronger inhibiting activity on DNA gyrase enzyme.

Synthesis, reactions, and biological study of some new thienopyrimidine derivatives as antimicrobial and anti‐inflammatory agents

Pyrimidine and thienopyrimidine derivatives play a very important role in organic chemistry because of their wide applications as bioactive compounds with multiple biological activities. However, a literature survey revealed that the merger of different groups in the thieno[2,3‐d]pyrimidine heterocyclic ring enhances its antibacterial, antifungal and anti‐inflammatory activities. This encouraged us to prepare a new series of thieno[2,3‐d]pyrimidine heterocyclic compounds and to test them as antimicrobial and anti‐inflammatory agents. These compounds have shown remarkable activity toward fungi, bacteria, and inflammation. Thus, these compounds have been prepared by the chloroacylation of 5‐amino‐4‐phenyl‐2‐(p‐tolylamino)thieno[2,3‐d] pyrimidine‐6‐carboxamide (4) using chloroacetyl chloride under neat condition to afford the target compound (6), which was used as precursor for the synthesis of a number of bioactive compounds. Thus reaction of the chloromethylpyrimidine derivative (6) with triphenylphosphine in dry benzene gave the corresponding ((4‐oxo‐9‐phenyl‐7‐(p‐tolylamino)‐3,4‐dihydropyrimido[4′,5′:4,5]thieno[2,3‐d]pyrimidin‐2‐yl)methyl) triphenylphosphonium chloride (7). Compounds 8a–8c and 9a–9c were obtained by the reaction of 7 with some selected aromatic aldehydes and ketones in methanol and sodium methoxide under Wittig reaction condition. The structures of the all new synthesized compounds were established on the basis of their analytical and spectral data (IR, 1H NMR, 13C NMR, and MS).

Dinuclear N-heterocyclic carbene silver complexes: Synthesis, luminescence and catalytic studies

A new dibenzimidazole compound (1) and three dibenzimidazolium salts (2a-2c) were prepared. Reactions of these salts with silver(I) oxide in methanol led to dinuclear N-heterocyclic carbene silver complexes (3a-3c). All of the compounds were characterized by 1H NMR, 13C NMR and elemental analyses. Molecular weights of the silver complexes were confirmed by MALDI-TOF mass spectrometry. Preliminary catalytic studies using all the silver complexes were performed on three-component coupling reaction of p-formaldehyde, piperidine and phenylacetylene. Complexes 3a and 3c exhibited good catalytic activities under neat conditions. The silver complexes showed luminescence properties in CH3CN at room temperature.

Stabilization of SF5– with Glyme-Coordinated Alkali Metal Cations

The stabilization of complex fluoroanions derived from weakly acidic parent fluorides is a significant and ongoing challenge. The [SF5]- anion is recognized as one such case, and only a limited number of [SF5]- salts are known to be stable at room temperature. In the present study, glyme-coordinated alkali metal cations (K+, Rb+, and Cs+) are employed to stabilize [SF5]-, which provides a simple synthetic route to a [SF5]- salt. The reactivities of KF and RbF with SF4 are significantly enhanced by complexation with G4, based on Raman spectroscopic analyses. A new room-temperature stable salt, [Cs(G4)2][SF5] (G4 = tetraglyme), was synthesized by stoichiometric reaction of CsF, G4, and SF4. The vibrational frequencies of [SF5]- were assigned based on quantum chemical calculations, and the shift of the G4 breathing mode accompanying coordination to metal cations was confirmed by Raman spectroscopy. Single-crystal X-ray diffraction revealed that Cs+ is completely isolated from [SF5]- by two G4 ligands and [SF5]- is disordered along the crystallographic two-fold axis. Hirshfeld surface analysis reveals that the H···H interaction between two neighboring [Cs(G4)2]+ moieties is more dominant on the Hirshfeld surface than the interaction between the H atom in glyme molecules and the F atom in [SF5]-, providing a CsCl-type structural model where the large and spherical [Cs(G4)2]+ cations contact each other and the [SF5]- anions occupy interstitial spaces in the crystal lattice. The [SF5]- anion, combined with [Cs(G4)2]+, exhibits a very limited deoxofluorinating ability toward hydroxyl groups in both neat conditions and THF solutions.

Ball-Milled Co–N–C Nanocomposite for Benzylic C–H Bond Oxidation: a Facile, Practical, and Recyclable Catalyst under Neat Conditions and Atmospheric Pressure Oxygen

A novel Co–N–C nanocomposite catalyst was prepared using a mechanical ball-milling method from melamine and Co(NO3)2, and no high-temperature calcination procedures were required. The superior nanocomposite catalyst shows excellent catalytic activity in the selective liquid-phase oxidation of benzylic C–H bonds with atmospheric pressure oxygen as an oxidant under solvent-free conditions. With 0.5 mol % of the Co–N–C nanocomposite catalyst, up to a 95% conversion and 98% selectivity are achieved in the oxidation of ethylbenzene to acetophenone. Furthermore, the catalyst shows good recyclability and can be simply recovered by filtration and reused several times without a significant loss in catalytic activity.

A sustainable strategy for production and functionalization of nanocelluloses

Abstract A sustainable strategy for the neat production and surface functionalization of nanocellulose from wood pulp is disclosed. It is based on the combination of organocatalysis and click chemistry (“organoclick” chemistry) and starts with nanocellulose production by organic acid catalyzed hydrolysis and esterification of the pulp under neat conditions followed by homogenization. This nanocellulose fabrication route is scalable, reduces energy consumption and the organic acid can be efficiently recycled. Next, the surface is catalytically engineered by “organoclick” chemistry, which allows for selective and versatile attachment of different organic molecules (e.g. fluorescent probes, catalyst and pharmaceuticals). It also enables binding of metal ions and nanoparticles. This was exemplified by the fabrication of a heterogeneous nanocellulose-palladium nanoparticle catalyst, which is used for Suzuki cross-coupling transformations in water. The disclosed surface functionalization methodology is broad in scope and applicable to different nanocelluloses and cellulose based materials as well.

A New Lewis Acidic Zr Catalyst for the Synthesis of Furanic Diesel Precursor from Biomass Derived Furfural and 2-Methylfuran

Herein, we reported the first time to use Lewis type acidic Zr/SBA-15 catalyst for the hydroxyalkylation/alkylation (HAA) reaction of biomass derived furfural and 2-methylfuran (2-MF) to produce diesel precursors. Characterizations such as XRD, XPS, SEM and TEM, were used to provide detailed structure features of mesoporous catalysts of varied Si/Zr ratios. Among the catalysts, Zr/SBA-15(20) (Si/Zr ratio(mol:mol) = 20:1) possessed the highest catalytic activity in the HAA reaction, providing 93.9% yield of the target product at 140 °C under neat condition. Lewis acid was revealed as the dominant active sites for the HAA reaction. Reaction parameters including reaction temperature, catalyst loading and furfural/2-MF ratio were investigated and found to affect the reaction efficiency and product yields. Besides, the optimal Zr/SBA-15(20) catalyst maintained outstanding recyclability in the recycling test, offering almost comparable reaction yields as freshly prepared catalyst. This work not only opens up a new concept by using Lewis catalyst for HAA reaction to synthesize diesel precursors from biomass, but also enriches the catalyst inventory of HAA reaction by providing a pH-neutral, recyclable and stable catalyst.

MIL-101 supported highly active single-site metal catalysts for tricomponent coupling

Metal-organic frameworks with regular pore structures provide powerful platforms for the design of single-site metal catalysts for chemical transformation. In this paper, we develop a facile, stable and recyclable MOF-supported Cu(II) catalyst, MIL-101-SO3Cu. It shows extremely high activity for the A3 coupling of alkynes, aldehydes and amines. The turnover frequency can reach 6.8 × 105 h−1 under neat conditions, which is the highest so far reported for the reaction. The high activity is because the specific structure of the MIL-101-SO3 support enables a single-site dispersion and an unhindered open environment for the metal ion. MIL-101-SO3Cu also exhibits high activity for the one-pot cascade reactions combining A3 coupling and 5-endo-dig cyclization.

Copper‐Catalyzed Direct Amination of Aryl C–H Bonds with Alkylamines via Bidentate Chelation Assistance from 8‐Aminoquinoline Motif at Room Temperature

AbstractWe report a novel, versatile method for Cu(I)‐catalyzed direct amination of N‐quinolylbenzocarboxamides at the aryl group with alkylamines at ortho sp2‐C−H bond with assistance from 8‐aminoquinoline motif and for as many as 27 substrate combinations at room temperature under neat conditions in the presence of air without requiring any base or additives.

Citric acid stabilized on the surface of magnetic nanoparticles as an efficient and recyclable catalyst for transamidation of carboxamides, phthalimide, urea and thiourea with amines under neat conditions

Citric acid-coated magnetic nanoparticles (Fe3O4–CA NPs) were successfully prepared and characterized. This magnetic nanocatalyst was employed as an efficient, recyclable, and environmentally benign heterogeneous catalyst for the transamidation of carboxamides, phthalimide, urea and thiourea with amines. Several derivatives of formylated and transamidated products were synthesized in good to excellent yields in the presence of this catalytic system. And, the catalyst could be easily separated from the reaction mixture using an external magnet and can be reused six times without any significant loss in its catalytic activity.

Aerobic Oxidative Homo- and Cross-Coupling of Amines Catalyzed by Phenazine Radical Cations

Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.

Revisiting the Betti Synthesis: Using a Cheap, Readily Available, Recyclable Clay Catalyst under Solventless Conditions

One‐pot multicomponent reactions have gained significant importance in recent years because they are usually more selective, simple, efficient, atom‐economic and green than their multistep counterparts. The Betti synthesis involves the combination of aldehydes, amines and 2‐naphthol to form compounds which can serve as catalysts or as biologically active compounds. In this study, Montmorillonite K30 was used as a heterogeneous catalyst for the Betti reaction at 60 °C in relatively short reaction times. Positively, it is cheap, readily and commercially available and requires no preparation, it can be used in neat conditions whilst minimizing excess reagent amounts. Most importantly, it is fully recoverable and can be recycled up to 5 times. In reactions involving secondary aliphatic amines, very good to excellent results were obtained whilst primary ones including benzylamine gave appreciable yields. In addition, the heteroaromatic aldehyde 4‐pyridinecarboxaldehyde and the polyaromatic aldehyde 1‐naphthaldehyde also gave encouraging results.

An Efficient Synthesis of Oxazolidines by Tandem Ring‐Opening / Closing Reaction of Ts‐Aziridine Using Formic Acid

AbstractSynthesis of oxazolidines has been reported from aziridines by the reaction with formic acid and formaldehyde in neat conditions. We have also observed a regio‐selective nucleophilic ring opening of aziridines by HCOOH under same conditions in absence of formaldehyde where the HCOO− ion acts as a nucleophile. In this present method formic acid is not acting as reducing agent as classical organic reactions. The formic acid initially activates the aziridines whereas the formate group generated from formic acid acts as a nucleophile itself instead of the source of hydride ion affording the nucleophilic ring opening products. The synthesized formate ester was successfully hydrolyzed to the corresponding hydroxyl compound which is the key building block for the synthesis of heterocycles. Operational simplicity, mild and neat reaction conditions, broad substrates scope, good yields and uses of less expensive reagents are the notable advantages of the present procedures.

Acid catalyzed aldol condensations of ketones with glyoxylic acid: A simple single-step synthesis of 4-oxo-2,5-heptdienedioic acids

The acid catalyzed condensations of ketones with glyoxylic acid at 80 °C, under neat conditions gives 4-oxo-2,5-heptdienedioic acids in 56–88% yield. The solid state photochemical dimerization of 4-oxo-2,5-heptdienedioic acid under UV light gives 2,7-dioxo-tricyclo[6.2.0.03,6]decane-4,5,9,10-tetracarboxylic acid in 90% yield.