Search Results (18)

A synthesis of organophosphorus compounds containing an aziridine ring, previously described by our group, has been performed and the catalytic activity of the aforementioned chiral heterorganic compounds has been investigated in the asymmetric nitroaldol (Henry) reaction between aromatic/aliphatic aldehydes and nitromethane in the presence of catalytic amounts of copper (II) acetate. In several cases, the chiral β-nitroalcohols have been obtained with high chemical yields and exhibited very high enantiomeric excess values (over 95%). Notably, the use of two enantiomerically pure catalysts, differing in the absolute configuration of the aziridine unit, resulted in the formation of two enantiomeric products of the Henry reaction. Full article

This article is a continuation of our previous research on the catalytic capability of a chiral copper complex based on commercially available (S)-2-aminomethylpyrrolidine and 3,5-di-tert-butylsalicylaldehyde with various counter-anions in the asymmetric Henry reaction. Our findings indicate that depending on the type of base used, chiral nitroalcohols with yields up to 98% and ee values up to 77%, as well as β-nitrostyrenes with yields up to 88%, can be produced. Additionally, it has been found that the outcome of the reaction and the catalytic properties of copper (II) complexes (S)-Cu1 and (S)-Cu2 are influenced by the structure of the aldehyde used. Full article

In this article, chitosan copper oxide nanocomposite was synthesized by the solution casting method under microwave irradiation. The nanocomposite solution was microwave irradiated at 300 watt for 3 min under optimal irradiation conditions. By suppressing particle agglomeration, the chitosan matrix was successfully used as a metal oxide stabilizer. The goal of this research was to create, characterize, and test the catalytic potency of these hybrid nanocomposites in a number of well-known organic processes. The prepared CS-CuO nanocomposites were analyzed by different techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Moreover, energy-dispersive X-ray spectroscopy (EDS) was used to measure the copper content in the prepared nanocomposite film. The finger-print peaks in the FTIR spectrum at around 632–502 cm⁻¹ confirmed the existence of the CuO phase. The CS-CuO nanocomposite has been shown to be an efficient base promoter for nitroolefin synthesis via the nitroaldol reaction (Henry reaction) in high yields. The reaction variables were studied to improve the catalytic approach. Higher reaction yields, shorter reaction times, and milder reaction conditions are all advantages of the technique, as is the catalyst’s reusability for several uses. Full article

Granulicella tundricola hydroxynitrile lyase (GtHNL) catalyses the synthesis of chiral (R)-cyanohydrins and (R)-β-nitro alcohols. The triple variant GtHNL-A40H/V42T/Q110H (GtHNL-3V) was immobilised on Celite R-633 and used in monophasic MTBE saturated with 100 mM KPi buffer pH 7 for the synthesis of (R)-2-nitro-1-phenylethanol (NPE) in batch and continuous flow systems. Nitromethane was used as a nucleophile. A total of 82% of (R)-NPE and excellent enantioselectivity (>99%) were achieved in the batch system after 24 h of reaction time. GtHNL-3V on Celite R-633 was successfully recycled five times. During more recycling steps a significant decrease in yield was observed while the enantioselectivity remained excellent over eight cycles. The use of a flow system enabled the continuous synthesis of (R)-NPE. A total of 15% formation of (R)-NPE was reached using a flow rate of 0.1 mL min⁻¹; unfortunately, the enzyme was not stable, and the yield decreased to 4% after 4 h on stream. A similar yield was observed during 15 h at a rate of 0.01 mL min⁻¹. Surprisingly the use of a continuous flow system did not facilitate the process intensification. In fact, the batch system displayed a space-time-yield (STY/mg_enzyme) of 0.10 g L⁻¹ h⁻¹ mg_enzyme⁻¹ whereas the flow system displayed 0.02 and 0.003 g L⁻¹ h⁻¹ mg_enzyme⁻¹ at 0.1 and 0.01 mL min⁻¹, respectively. In general, the addition of 1 M nitromethane potentially changed the polarity of the reaction mixture affecting the stability of Celite-GtHNL-3V. The nature of the batch system maintained the reaction conditions better than the flow system. The higher yield and productivity observed for the batch system show that it is a superior system for the synthesis of (R)-NPE compared with the flow approach. Full article

Novel chiral thiophene-2,5-bis(β-amino alcohol) ligands (L1–L5) were designed and synthesized from thiophene-2,5-dicarbaldehyde (3) with chiral β-amino alcohols (4a–e) in 4 steps with overall 23% yields. An in situ generated L-Cu(OAc)₂·H₂O catalyst system was found to be highly capable catalyst for the asymmetric Henry reaction of nitromethane (7) with various substituted aromatic aldehydes (6a–m) producing chiral nitroaldols product (8a–m) with excellent enantiomeric purity (up to 94.6% ee) and up to >99% chemical yields. 20 mol% of L4-Cu(OAc)₂ catalyst complex in EtOH was effective for the asymmetric Henry transformation in 24 h, at ambient temperature. Ease of ligand synthesis, use of green solvent, base free reaction, mild reaction conditions, high yields and excellent enantioselectivity are all key factors that make this catalytic system robust and highly desirable for the access of versatile building block β-nitro alcohol in practical catalytic usage via asymmetric Henry reaction. Full article

Interesting properties of N-oxides and pyridine oxazoline compounds have become the starting point to synthesize compounds connecting both groups. A multi-step synthesis of a series of chiral oxazoline substituted pyridine N-oxides, alkyl derived of pyridine N-oxides, bipyridine N-oxides, and isoquinoline N-oxides, based on amino alcohols derived from natural amino acids or other previously prepared, is presented herein. Various synthetic pathways have been designed and tested according to the properties and limitations imposed by the target products. The encountered problems related to the stability of the products were discussed. The resulting compounds (eighteen structures) were tested as catalysts in th e allylation of benzaldehyde (obtaining up to 79% ee) as well as in nitroaldol reaction (obtaining up to 48% ee). Full article

A derivative series of 3,4-dimethoxy-β-nitrostyrene was synthesized through nitroaldol reaction, including a new compound of 3,4-ethylenedioxy-β-bromo-β-nitrostyrene. The antimicrobial activity effect of 3,4-alkyloxy modification of β-nitrostyrene was investigated. A molecular docking study was also performed to obtain information about their interactions with protein tyrosine phosphatase 1B (PTP1B). The active residues of cysteine-215 and arginine-221 of PTP1B play a key role in signaling pathways that regulate various microorganism cell functions. It also acts as a negative regulator in signaling pathways of insulin that are involved in type 2 diabetes and other metabolic diseases. These derivatives exhibited potential antifungal activity. The studied compounds were also had potential as fragments to be PTP1B inhibitors by interacting with serine-216 and arginine-221 residues, according to their molecular docking. 3,4-Ethylenedioxy-β-methyl-β-nitrostyrene was the most successful potential candidate as a PTP1B inhibitor. However, further research is needed to investigate their potential for medicinal use. Full article

The mononuclear zinc(II) complex cis-[ZnL₂(H₂O)₂] (1; L = 4-(pyridin-3-ylcarbamoyl)benzoate) was synthesized and characterized. By soaking crystals of 1 in a mixture of DMF-H₂O solution containing a slight excess of Cu(NO₃)₂ × 3H₂O a transmetalation reaction occurred affording the related copper(II) complex trans-[CuL₂(H₂O)₂] (2). The structures of the compounds were authenticated by single crystal X-ray diffraction revealing, apart from a change in the isomerism, an alteration in the relative orientation of the chelating carboxylate groups and of the pyridine moieties. H-bond interactions stabilize both geometries and expand them into two-dimensional (2D) networks. The transmetalation was confirmed by SEM–EDS analysis. Moreover, the thermodynamic feasibility of the transmetalation is demonstrated by density-functional theory (DFT) studies. The catalytic activities of 1 and 2 for the oxidation of styrene and for the nitroaldol (Henry) C-C coupling reaction were investigated. The copper(II) compound 2 acts as heterogeneous catalyst for the microwave-assisted oxidation of styrene with aqueous hydrogen peroxide, yielding selectively (>99%) benzaldehyde up to 66% of conversion and with a turnover frequency (TOF) of 132 h⁻¹. The zinc(II) complex 1 is the most active catalyst (up to 87% yield) towards the nitroaldol (Henry) coupling reaction between benzaldehyde and nitro-methane or -ethane to afford the corresponding β-nitro alcohols. The reaction of benzaldehyde with nitroethane in the presence of 1 produced 2-nitro-1-phenylpropanol in the syn and the anti diastereoisomeric forms, with a considerable higher selectivity towards the former (66:34). Full article

_∞³[Cu₂(mand)₂(hmt)]·H₂O (where mand is totally deprotonated mandelic acid (racemic mixture) and hmt is hexamethylenetetramine) proved to be a stable metal–organic framework (MOF) structure under thermal activation and catalytic conditions, as confirmed by both the in situ PXRD (Powder X-ray diffraction) and ATR–FTIR (Attenuated total reflection-Fourier-transform infrared spectroscopy) haracterization. The non-activated MOF was completely inert as catalyst for the Henry reaction, as the accessibility of the substrates to the channels was completely blocked by H-bonded water to the mand entities and CO₂ adsorbed on the Lewis basic sites of the hmt. Heating at 140 °C removed these molecules. Only an insignificant change in the relative ratios of the XRD facets due to the capillary forces associated to the removal of the guest molecules from the network has been observed. This treatment afforded the accessibility of nitromethane and various aldehydes (4-bromobenzaldehyde, 4-nitrobenzaldehyde, and p-tolualdehyde) to the active catalytic sites, leading to conversions up to 48% and selectivities up to 98% for the desired nitroaldol products. The behavior of the catalyst is solvent-sensitive. Protic solvents completely inhibited the reaction due to the above-mentioned strong H-bonds. Accordingly, very good results were obtained only with aprotic solvents such as acetonitrile and 1,4-dioxane. The synthesized MOF is completely recyclable as demonstrated for five successive cycles. Full article

An increasing interest in the synthesis and use of optically active pyridine N-oxides as chiral controllers for asymmetric reactions has been observed in the last few years. Chiral heteroaromatic N-oxides can work as powerful electron-pair donors, providing suitable electronic environments in the transition state formed within the reaction. The nucleophilicity of the oxygen atom in N-oxides, coupled with a high affinity of silicon to oxygen, represent ideal properties for the development of synthetic methodology based on nucleophilic activation of organosilicon reagents. The application of chiral N-oxides as efficient organocatalysts in allylation, propargylation, allenylation, and ring-opening of meso-epoxides, as well as chiral ligands for metal complexes catalyzing Michael addition or nitroaldol reaction, can also be found in the literature. This review deals with stereoselective applications of N-oxides, and how the differentiating properties are correlated with their structure. It contains more recent results, covering approximately the last ten years. All the reported examples have been divided into five classes, according to the chirality elements present in their basic molecular frameworks. Full article

The aroylhydrazone Schiff bases 2-hydroxy-(2-hydroxybenzylidene)benzohydrazide and (2,3-dihydroxybenzylidene)-2-hydroxybenzohydrazide have been used to synthesize the bi- and tri-nuclear Ni(II) complexes [Ni₂(L¹)₂(MeOH)₄] (1) and [Ni₃(HL²)₂(CH₃OH)₈]· (NO₃)₂ (2). Both complexes have been characterized by elemental analysis, spectroscopic techniques [IR spectroscopy and electrospray ionization-mass spectrometry (ESI-MS)], and single-crystal X-ray crystallography. The coordination behavior of the two ligands is different in the complexes: The ligand exhibits the keto form in 2, while coordination through enol form was found in 1. Herein, the catalytic activity of 1 and 2 has been compared with the nitroaldol condensation reaction under various conditions. Complex 2 exhibits the highest activity towards solvent-free conditions. Full article

In this work, we investigated two strategies for the synthesis of the challenging ketones 2-acylbenzonitriles and we report their use as electrophiles in asymmetric organocatalytic cascade reactions with nitromethane. Promising results were obtained in the presence of chiral bifunctional ammonium salts under phase transfer conditions, which led to novel 3,3-disubstituted isoindolinones in quantitative yields and moderate enantioselectivity. Full article

This present mini-review covers recently published results on Cu(I) and Cu(II) complexes immobilized on polystyrene carriers, which are used as heterogeneous, eco-friendly reusable catalysts applied for carbon–carbon and carbon–nitrogen forming reactions. Recent advances and trends in this area are demonstrated in the examples of oxidative homocoupling of terminal alkynes, the synthesis of propargylamines, nitroaldolization reactions, azide alkyne cycloaddition, N-arylation of nitrogen containing compounds, aza-Michael additions, asymmetric Friedel–Crafts reactions, asymmetric Mukaiyama aldol reactions, and asymmetric 1,3-dipolar cycloaddition of azomethine ylides. The type of polystyrene matrix used for the immobilization of complexes is discussed in this paper, and particularly, the efficiency of the catalysts from the point of view of the overall reaction yield, and possible enantioselectivity and potential reusing, is reviewed. Full article

Here we describe a preliminary investigation on the ability of natural keratin to catalyze the nitroaldol (Henry) reaction between aldehydes and nitroalkanes. Both aromatic and heteroaromatic aldehydes bearing strong or moderate electron-withdrawing groups were converted into the corresponding β-nitroalcohol products in both DMSO and in water in the presence of tetrabutylammonium bromide (TBAB) as a phase transfer catalyst. Negligible background reactions (i.e., negative control experiment in the absence of keratin protein) were observed in these solvent systems. Aromatic aldehydes bearing electron-donating groups and aliphatic aldehydes showed poor or no conversion, respectively. In general, the reactions in water/TBAB required twice the amount of time than in DMSO to achieve similar conversions. Moreover, comparison of the kinetics of the keratin-mediated nitroaldol (Henry) reaction with other biopolymers revealed slower rates for the former and the possibility of fine-tuning the kinetics by appropriate selection of the biopolymer and solvent. Full article

In this manuscript we report a critical evaluation of the ability of natural DNA to mediate the nitroaldol (Henry) reaction at physiological temperature in pure water. Under these conditions, no background reaction took place (i.e., control experiment without DNA). Both heteroaromatic aldehydes (e.g., 2-pyridinecarboxaldehyde) and aromatic aldehydes bearing strong or moderate electron-withdrawing groups reacted satisfactorily with nitromethane obeying first order kinetics and affording the corresponding β-nitroalcohols in good yields within 24 h. In contrast, aliphatic aldehydes and aromatic aldehydes having electron-donating groups either did not react or were poorly converted. Moreover, we discovered that a number of metal-free organic buffers efficiently promote the Henry reaction when they were used as reaction media without adding external catalysts. This constitutes an important observation because the influence of organic buffers in chemical processes has been traditionally underestimated. Full article