Search Results (292)

High-density aviation fuels and diesel-range cycloalkanes are in high demand for the transportation sector, but the development of sustainable and high-efficiency synthesis routes from biomass-derived platform chemicals remains a key challenge. High-density aviation fuel and diesel-grade cycloalkanes were successfully synthesized from biomass-derived isophorone and furfural through a continuous process of selective hydrogenation, aldol condensation, and hydrodeoxygenation reaction. (E) 2-(Furan-2-methylene)-3,5,5-trimethylcyclohex-1-one (1A) was obtained by selective hydrogenation of isophorone to obtain 3,3,5-trimethylcyclohexanone (TMCH), which was then subjected to aldol condensation with furfural. The system studied key reaction parameters such as solvent type, temperature, catalyst type, catalyst loading, and reaction time that affect the aldol condensation of TMCH and furfural. The yield of 1A reached 98.69%, under optimized conditions using NaOH as the catalyst at a molar ratio of 3,3,5-trimethylcyclohexanone:furfural = 1:1, NaOH 0.15 g, anhydrous ethanol as the solvent, and a reaction temperature of 313 K for 1 h. A series of nickel-based catalysts supported on porous materials, including SiO₂, CeO₂, Al₂O₃, Hβ, and HZSM-5, were prepared and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These catalysts were evaluated for the hydrodeoxygenation of 1A. Among them, the 10% Ni-SiO₂ catalyst exhibited the highest catalytic activity, affording a C₉–C₁₄ cycloalkane yield of 88.32% and a total carbon yield of 99.6%. This work demonstrates a promising and sustainable strategy for producing branched cycloalkanes in the diesel and jet fuel range from lignocellulosic biomass-derived platform chemicals. Full article

Friedelin, a pentacyclic triterpene, has been reported to inhibit potential reactive oxygen species (ROS)-scavenging activity. Accordingly, we modified the structure of this compound with the aim of obtaining derivatives. A new derivative (compound 4), with an α,β-unsaturated ketone moiety, was synthesized via an aldol condensation. Structural characterization of this compound was performed using nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry. Full article

(S)-2-methyl-5-(prop-1-en-2-yl)cyclopent-1-ene-1-carbaldehyde (2) is a component of the essential oils of several plants and has also been used in many syntheses, usually of terpenes. Although the preparation of compound 2 has been reported several times, no side products have been reported previously. In this Short Note, we present the identification of one such side product. This new compound (3) arises from a vinylogous aldol autocondensation, occurring after the formation of 2, even when the reaction runs for a short time. However, it can diminish the yield of 2 when the reaction is allowed to continue for a longer time. Full article

This study evaluates the feasibility of achieving chemoselective aldol reactions over competing Henry reactions and employs competition experiments to establish proof of concept. A typical reaction involved using in-water reaction conditions where a concentrated organic layer containing an aldol nucleophile (1.5 equiv), a Henry nucleophile (1.5 equiv), an aldehyde electrophile (1.0 equiv), and a proline-based amino acid catalyst (2.5 mol%) constituted one phase, while the second phase was water (15 equiv). Highly enantioenriched aldol products were formed in practical yields, and a variety of Henry nucleophiles (nitroalkanes, allylic nitro compounds, and ethyl nitroacetate) were tolerated. This systematic examination of nitro compounds (pK_a 5.5–10.0) established a pK_a of ≈7.0 as the critical threshold at which nitronate formation results in Henry product formation under catalysis with 1. Reactions alternatively performed in MeOH/H₂O (3:2 equiv) solvent combinations, at times, provided improved chemoselectivity or product dr over the use of water (15 equiv) alone but required longer reaction times to produce similar yields. Reactions constrained by solubility were investigated using mechanochemical methods, but these conditions failed to deliver practical yields of either competition product. In summary, defining this category of aldol chemoselectivity may provide new tactical opportunities for the synthesis of complex molecular targets. Full article

There is an urgent need to evaluate the toxicity of xenobiotics and environmental mixtures for preventing loss in water quality for the sustainability of aquatic ecosystems. A simple prebiotic chemical pathway based on malate formation from pyruvate (pyr) and glyoxalate (glyox) is proposed as a quick and cheap screening tool for toxicity assessment. The assay is based on the pyr and glyox (aldol) condensation reactions, leading to biologically relevant precursors such as oxaloacetate and malate. Incubation of pyr and glyox at 40–70 °C in the presence of reduced iron Fe(II) led to malate formation following the first 3 h of incubation. The addition of various xenobiotics/contaminants (silver, copper, zinc, cerium IV, samarium III, dibutylphthalate, 1,3-diphenylguanidine, carbon-walled nanotube, nanoFe₂O₃ and polystyrene nanoparticles) led to inhibitions in malate synthesis at various degrees. Based on the concentration inhibiting malate concentrations by 20% (IC20), the following potencies were observed: silver < copper ~ 1.3-diphenylguanidine ~ carbon-walled nanotube < zinc ~ samarium < dibutylphthalate ~ samarium < Ce(IV) < nFeO₃ < polystyrene nanoplastics. The IC20 values were also significantly correlated with the reported trout acute lethality data, suggesting its potential as an alternative toxicity test. The pyr-glyox pathway was also tested on surface water extracts (C18), identifying the most contaminated sites from large cities and municipal wastewater effluents dispersion plume. The inhibition potencies of the selected test compounds revealed that not only pro-oxidants but also chemicals hindering enolate formation, nucleophilic attack of carbonyls and dehydration involved in aldol-condensation reactions were associated with toxicity. The pyr-glyox pathway is based on prebiotic chemical reactions during the emergence of life and represents a unique tool for identifying toxic compounds individually and in complex mixtures. Full article

Herein, we prepared nanoparticles of chitosan–manganese(II) complexes in different molar ratios (1:2, 1:1, and 2:1) and fully characterized them using dynamic and electrophoretic light scattering, X-ray diffraction, SEM, FTIR, and thermal analysis. Nanoparticles Chitosan + Mn²⁺ (1:1) have a high catalytic activity in the oxidative coupling of benzylamine, resulting in the imine formation and also in selective aldol reaction. Chitosan + Mn²⁺ (1:1) catalyze the reactions in the greenest solvents: water and water/ethanol mixture. Moreover, Chitosan + Mn²⁺ (1:1) is very easy to prepare and convenient to use. The catalyst is separated from the reaction mixture by a simple nanoporous filter or centrifugation and does not lose catalytic activity after at least ten uses. The chitosan–manganese(II) complexes reduce the milk fermentation time, demonstrating the effectiveness in accelerating the fermentation process by Streptococcus thermophilus. They also contribute to increasing the shelf life of fermented milk products by inhibiting the undesirable post-acidification process. We found that the optimal ratio of chitosan and Mn²⁺ to manifest the apogee of the desired effects (acceleration of milk fermentation and increase in the shelf life of the fermented product) is 1:2. Full article

In the present study, (E)-1-(2-(pyridin-2-yl)benzo[d]thiazol-6-yl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (4) was designed and synthesized via a three-step reaction sequence. Initially, 6-acetylbenzo[d]thiazol-2(3H)-one (1) was hydrolyzed to the corresponding 5-acetyl-2-aminothiophenol 2 and then cyclized with pyridine-2-carbaldehyde. The final product was synthesized by a base-catalyzed aldol condensation of 1-(2-(pyridin-2-yl)benzo[d]thiazol-6-yl)ethan-1-one (3) and 3,4,5-trimethoxybenzaldehyde and was comprehensively characterized. Full article

The mixture of enantiomers in pharmaceuticals can lead to adverse effects, as demonstrated by thalidomide, where one enantiomer exhibited therapeutic properties while the other was teratogenic. Currently, efforts are focused on developing efficient catalysts capable of selectively producing a single stereoisomer, particularly in the synthesis of neuropharmaceuticals and NSAIDs. In this context, a new chiral catalyst was synthesized, featuring a palladium core and the dipeptide L-lysine-glycine as a ligand. The catalyst was characterized using various spectroscopic techniques and exhibited enantiomeric excesses of up to 40% in aldol reactions. Additionally, it efficiently promoted Heck cross-coupling reactions, indicating its potential catalytic versatility. Full article

2-Benzylidene-1-indanones constitute a family of heterocyclic compounds with a wide range of pharmacological and material applications. Here we present preliminary results of new chemistry in this field. An acid-mediated aldolic condensation of 1-indanone with o-nitrobenzaldehyde provided (E)-2-(2-nitrobenzylidene)-2,3-dihydro-1H-inden-1-one, which, when subjected to catalytic hydrogenation, led directly to 4b,10,10a,11-tetrahydro-5H-indeno[1,2-b]quinoline, as a result of several successive spontaneous reactions. On the other hand, a base-mediated aldolic condensation of 1-indanone with o-methoxycarbonylbenzaldehyde yielded methyl (E)-2-((1-oxo-1,3-dihydro-2H-inden-2-ylidene)methyl)benzoate which, when treated with LDA, led to the formation of 1′-(diisopropylamino)-2,2′-spirobi[indene]-1,3′(1′H,3H)-dione. Full article

Curcumin (CUR) is the primary metabolite isolated from the Curcuma longa L. rhizome. Most synthetic and biological studies have focused mainly on the curcumin molecule due to its essential biological activity as an antioxidant, anti-cancer, and anti-Alzheimer’s disease agent. However, the natural extract of turmeric also contains two essential curcuminoids (demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC)), which altogether comprise the so-called C-3 complex. They are present in commercial compositions for treating biliary or digestive ailments. The vegetal rhizome’s extraction typically leads to a mixture of the three main curcuminoids, CUR, DMC, and BDMC, in variable proportions, and each of these metabolites has reported specific synthetic routes. Herein, we have performed the synthesis and isolation of the three major curcuminoids using the method called scrambling of aldehydes followed by aldol di-condensation reactions. A density functional theory (DFT) approach supported the experimental results by inspecting the predicted energies for the aldol condensation. Thus, the di-condensation reaction is substantially favoured (ΔG° = −2685.9 kJ/mol) over the mono-condensation reaction (ΔG° = −1393.753 kJ/mol). Our approach allows us to mimic closely the proportions of these curcuminoids found in extracts from natural sources that follow the order CUR > DMC > BDMC, respectively. The proportion of aldehydes can be modified in the scrambling reaction with an adequate mixture of aldehydes to render the order DMC > CUR > BDMC. This is an advantageous way to increase the amount of the unsymmetric DMC metabolite. Full article

The degree of bovine serum albumin (BSA) released from particles based on chitosan and hydroxyapatite prepared by encapsulation and chemisorption methods, crosslinked by aldol condensation, was studied. The obtained materials’ composition was qualitatively determined by IR spectroscopy; phase identification and surface morphology were analyzed by X-ray diffraction and scanning electron microscopy, respectively. A spectrophotometric method was used to quantitatively assess the loading and release degree of encapsulated/chemisorbed BSA from polymer microspheres. To determine the release mechanism, the data on the amount of BSA released were analyzed according to the zero- and first-order, Higuchi, and Korsmayer–Peppas models. Full article

A tandem synthetic sequence involving photo-induced intramolecular [2+2] cycloaddition followed by acid-promoted ring expansion was developed to access the novel bicyclic triketone framework. The process begins with the UV (254 nm) irradiation of cyclic vinylogous ester, affording a highly strained cyclobutane-fused diketone in an 86% yield. This unique intermediate feature is of a fused four- and six-membered ring system with spatially compressed carbonyl groups. Upon acidic hydrolysis in aqueous MeCN, the strained system undergoes retro-aldol ring expansion, delivering [5.3.0] bicyclic triketones bearing a seven- and five-membered fused ring with three strategically oriented carbonyl units in a 75% yield. Structural elucidation was performed using NMR spectroscopy, UV-Vis, HRMS, and single-crystal X-ray crystallography. The method highlights a concise route for constructing a fused bicyclic triketone of relevance to synthetic and medicinal chemistry. Full article

Solketal is an important chemical product with widespread applications, and the raw materials glycerol and acetone are inexpensive, making it highly economically viable. The glycerol-acetone condensation reaction is a typical acid-catalyzed reaction. Traditional homogeneous acidic catalysts cause significant environmental pollution and are difficult to recover. Herein, PEG-800 was used as an additive, and a one-pot process was employed to prepare a series of aluminum phosphate catalysts (xP-Al-O) with different P/Al molar ratios. The physical and chemical properties of the prepared xP-Al-O catalysts were thoroughly investigated using XRD, FTIR, SEM, Py-FTIR, BET, and NH₃ (CO₂)-TPD methods. The results indicated that different P/Al molar ratios indeed affect the catalyst structure, and all prepared xP-Al-O samples exist in the form of amorphous aluminum phosphate, with weak acidic sites dominating the surface. The prepared catalysts were investigated for their catalytic behavior in the acetalization reaction of glycerol and acetone. The 1.1P-Al-O catalyst exhibited the highest acetone glycerol acetal yield and demonstrated good catalytic stability. Full article

Lyngbyabellins O and P are complex natural products derived from non-ribosomal peptide synthetase/polyketide synthase (NRPS/PKS) biosynthetic pathways and have been isolated from marine cyanobacterial sources. Both metabolites are characterized by the presence of two thiazole rings and a distinctive dichlorinated β-hydroxy acid side chain. Notably, lyngbyabellin P is further distinguished by the incorporation of a (3R,4S)-statine moiety. Herein, we report the first total syntheses of lyngbyabellins O and P, which are achieved through the convergent coupling of three key synthetic fragments, namely, two enantiomerically enriched thiazole subunits and a hydroxycarboxylic acid derivative, the latter constructed via a stereoselective aldol reaction. The total syntheses were completed in 12 and 13 longest linear steps (LLSs) for lyngbyabellins O and P, respectively, furnishing the natural products in overall yields of 5.6% and 2.5%. Full article