10.1002/ejic.201000802
The study focuses on the synthesis and investigation of ruthenium complexes bearing N-H acidic pyrazole ligands and their application in catalytic hydrogenation reactions. The researchers treated chelate ligands containing pyrazole groups with various ruthenium precursors to form complexes with protic N-H groups near the catalytically active ruthenium center. These complexes were characterized by spectroscopic methods and DFT calculations, and their structure and reactivity were analyzed. The study aimed to understand the role of the acidic N-H groups in metal-ligand-bifunctional hydrogenation, where a hydrido ligand and a proton from a protic group are transferred simultaneously. The catalytic performance of these complexes was evaluated through the hydrogenation and transfer hydrogenation of acetophenone, and the results were connected to the ligand's electronic and structural properties. The research provides insights into the design of efficient catalysts for hydrogenation reactions by leveraging the acidic N-H groups in pyrazole ligands.
10.1016/j.tet.2016.07.018
The study presents a novel and efficient copper-catalyzed vinylic Finkelstein reaction for the synthesis of various halogenated alkenes, which are important structural elements in pharmaceuticals, agrochemicals, and natural products. The researchers developed a method to convert alkenyl iodides and bromides into their chlorinated and brominated counterparts with high yields and full retention of double bond geometry. This method's broad applicability and mild reaction conditions make it suitable for a range of functionalized substrates. The study demonstrates the potential of this reaction in total synthesis and medicinal chemistry by using it to synthesize the C1–C9 fragment of laingolide B and for the late-stage modification of drug-like molecules. The researchers also explored the extension of this halogen exchange to acetylenic and allenic Finkelstein reactions.
10.1016/j.tetlet.2004.09.136
The study focuses on the reactivity of substituted pyridinium N-(20-azinyl)aminides in the Suzuki–Miyaura cross-coupling reaction, a widely used method for forming sp2–sp2 carbon–carbon bonds. The researchers investigated the coupling of these compounds with various boronic acids, using Cs2CO3 as a base, which resulted in good yields and substitution on the negatively charged moiety. They optimized the reaction conditions and found that the process was efficient for a range of substrates, including those with electron-deficient diazine rings, albeit requiring longer reaction times. The study also explored a double Suzuki process with a dibromoaminide to yield diarylated ylides. The results provide a valuable strategy for the synthesis of functionalized 2-aminoazines, which are important in medicinal and heterocyclic chemistry, and the researchers are continuing their efforts to expand the application of this process to other N-aminides.
10.1080/10587250307066
The research presents the synthesis and characterization of a new mesogenic homologous series of Schiff base cinnamates that incorporate a naphthalene moiety. The study aimed to understand the impact of the ethylene linking group (cinnamoyl linkage) and the naphthalene moiety on the mesomorphic properties of these molecules. The reactants used in the synthesis included 4-(40-n-alkoxy cinnamoyloxy) benzaldehydes, 2-amino naphthalene, malonic acid, n-alkyl halide, K2CO3, p-hydroxy benzaldehyde, and solvents like ethanol, which were dried prior to use. The synthesized compounds were characterized using elemental analysis and various spectroscopic techniques, including infrared (IR), ultraviolet (UV), and proton nuclear magnetic resonance (1H NMR) spectroscopy. The study found that all synthesized compounds exhibited mesomorphism, and the mesophase properties were compared with other structurally related series. The results indicated that the presence of the naphthalene moiety and the cinnamoyl linkage influenced the mesophase transition temperatures and the overall thermal stability of the mesophases.
10.1021/jp907080r
The research focuses on the photoactivation of azido push-pull fluorogens, which are non-fluorescent chromophores that can be converted into bright fluorescent labels suitable for single-molecule imaging. The experiments involve illuminating these aryl azide-containing fluorogens, triggering a photochemical conversion to aryl amines, which restores charge-transfer absorption and fluorescence. The study characterizes photophysical parameters such as photoconversion quantum yield, photostability, and turn-on ratio for a variety of push-pull chromophores. The research also includes the synthesis of different azido push-pull fluorogens and their photoactivation in different environments, including living cells, to demonstrate their potential for super-resolution microscopy and fluorogenic photoaffinity labeling. The analyses used include UV-vis and fluorescence spectroscopy, NMR, HPLC-MS, and microscopy techniques to confirm the conversion of non-fluorescent azido fluorogens to fluorescent amino fluorophores and to measure their photophysical properties.
10.1021/ja01439a015
The study investigates methods for separating lead salts of saturated fatty acids from those of unsaturated fatty acids. The study employs various solvents, including alcohol, chloroform, and ether, to dissolve the lead salts. Chloroform and ether, being more volatile and having greater solvent action, are used to gradually precipitate the more insoluble salts of saturated fatty acids through a fractionation process. The study explores different oils and fats, such as linseed oil, cottonseed oil, olive oil, and mutton tallow, to determine the effectiveness of the separation methods. The results indicate that the fractionation method allows for sharper and more controlled separations, enabling the removal of saturated fatty acid salts with a high degree of purity, especially when the more unsaturated acids like linolenic acid are absent from the oils or fats. The study concludes that the fractionation procedure is a reliable and effective method for separating lead salts of saturated fatty acids from those of unsaturated fatty acids.
10.1016/S0040-4020(00)00626-8
The study presents an eco-friendly and cost-effective method for the tosylation of alcohols and selective monotosylation of diols using p-toluenesulfonic acid with metal-exchanged montmorillonite clay as a catalyst. The Fe3+-montmorillonite clay demonstrated the highest effectiveness among the tested catalysts, outperforming Zn2+, Cu2+, Al3+-exchanged montmorillonites and K10 montmorillonite. This method allows for the regioselective tosylation of diols to monotosylated derivatives with high purity, favoring the primary hydroxy group in the presence of secondary hydroxy groups. The catalyst's reusability over several cycles was consistent, as shown in the tosylation of cyclohexanol. This approach minimizes by-product formation, typically just water, and offers advantages such as ease of catalyst recovery, recyclability, and enhanced stability compared to traditional methods using sulfonyl chloride or anhydride with organic bases.
10.1039/d1gc02002a
The research focuses on developing hypercrosslinked polymers (HCPs) containing dimethylformamide (DMF) moieties as alternatives to DMF solvent for azide-based synthesis. The study synthesized HCP-DMF and HCP-DMF-SO3H, which have flexible DMF-like moieties that provide a polar microenvironment for catalysis. The research aimed to replace hazardous DMF solvent with ethanol (EtOH) in the synthesis of benzylic azides and 1,2,3-triazoles, common structures in bioactive molecules. The experiments involved the conversion of NaN3 to benzylic azides and the synthesis of 1,2,3-triazoles using these HCP catalysts in EtOH, avoiding the use of DMF. Analyses included Fourier-transform infrared spectroscopy (FT-IR), fluorescence spectroscopy using Nile red as a probe, thermogravimetric analysis (TGA), solid-state 13C NMR, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) to characterize the HCP materials. The catalytic performance of the materials was evaluated by monitoring the reaction yields and recyclability of the catalysts.
10.1016/j.tet.2009.01.066
The research focuses on the thermodynamic aspects of host-guest chemistry involving pyrogallol[4]arenes and peralkylated ammonium cations. The study employs isothermal titration calorimetry to determine the stability constants, standard free energy, enthalpy, and entropy changes for the complexation of pyrogallol[4]arenes with ammonium cations of varying sizes and shapes in ethanol at 298 K. The experiments involve the titration of quaternary ammonium salts dissolved in ethanol with solutions of pyrogallol[4]arene in the same solvent, with the analysis of the resulting thermodynamic parameters providing insights into the complexation behavior and the influence of guest size on complex stability. The reactants include resorcin[4]arenes 1 and 2, pyrogallol[4]arene 3, and a series of tetraalkylammonium cations 4–12. The analyses used encompass both experimental calorimetry and computational chemistry, with the latter utilizing the Kohn–Sham DFT model to optimize structures and calculate formation energies for selected host-guest complexes.
10.1021/ja0528331
The research explores a novel method for forming sp3-sp3 C-C bonds through the activation of C-H bonds in alcohols, a significant challenge in organic chemistry. The study aims to develop an efficient intermolecular reaction between primary aliphatic alcohols and olefins, facilitated by a combination of a Lewis acid (BF3?OEt2) and the Wilkinson catalyst (RhCl(PPh3)3). The researchers discovered that this combination effectively promotes a cross-coupling reaction, yielding secondary alcohols. Key findings include the necessity of the Lewis acid for the reaction to proceed and the influence of electronic effects on the reaction rates of different olefins. The study concludes that the reaction mechanism likely involves a radical pathway, supported by experiments using deuterated alcohols and radical scavengers. This work presents a new approach to C-C bond formation without sacrificing additional functional groups, offering a promising avenue for further exploration in organic synthesis.
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