Search

The application of poly(4-vinylpyridine) supported trifluoromethanesulfonic acid (PVP-TfOH, 1:10) as a convenient solid superacid catalyst system in Friedel–Crafts reactions is described. In the presence of PVP-TfOH, one pot solvent-free synthesis of a wide variety of diarylacetic acid derivatives was achieved by Friedel–Crafts hydroxyalkylation reaction of glyoxylic acid with arenes under mild conditions. Acylation of both activated and deactivated aromatic compounds with acetyl chloride was also achieved using PVP-TfOH complex under solvent-free conditions at room temperature. As the polymer supported triflic acid was found to be a very efficient and an easy-to-handle solid acid, it can be a useful addition to environmentally more adaptable strong acid catalyst systems.

A novel, simple, convenient, and efficient synthesis of the title compounds (IV) and (VII) via a metal-free, one-pot three component reaction procedure.

A mild and efficient method for the synthesis of polysubstituted tetrahydropyridines has been developed which involves a three-component reaction of an arylamine (2 equiv.), an araldehyde (2 equiv.) and ethyl (or methyl) acetoacetate (1 equiv.) in MeCN under ambient conditions, in the presence of yttrium nitrate, Y(NO3)3·4H2O. This appears to be the first time yttrium nitrate has been used as a catalyst for this type of synthesis of tetrahydropyridines.

Researchers around the world are studying on different carbon capture and storage (CCS) options to reduce global warming by reducing CO 2 emission from various sources. Among all these options carbonation technology has some promising benefits over other technologies such as exothermic heat, availability of feed stocks, safe carbonated product and value added product and by-product, etc. In carbonation technology CO 2 chemically reacts with Ca/Mg bearing oxides or hydroxides and transformed into an environmentally safe solid carbonate materials. This technology has attracted attention of several researchers around the world and scientists of Albany Research Centre, USA have been working on it for few years. Recently a project has been established in Newcastle, Australia to set up a carbonation plant. Considering the potential benefits mentioned above, the prospects of carbonation technology to reduce global warming by reducing CO 2 emission have been reviewed, discussed and evaluated in this study.

Saccharose is found to be an efficient and homogenous catalyst for the one-pot, three-component Mannich reaction of aromatic aldehydes (II), anilines (III), and acetophenone (I) at room temperature.

New triterpernoid 3α-hydroxy-urs-12,15-diene (I) is isolated together with three known compounds.

A novel and efficient direct synthetic route to trifluoromethylated dihydrochalcones (III), aryl vinyl ketones (V), and indanones like (VIII) is based on Friedel—Crafts reactions under superacidic conditions.

A method for the introduction of a pyrazine ring into ring A of pentacyclic triterpenes is presented (yields not given).

A mixture of chloro/bromotrimethylsilane and nitrate salt is found to be an effective reagent system for the α-chlorination/bromination of carbonyl compounds. The reaction occurs under mild conditions yielding the products in moderate to good yields.

Indanones and coumarins are important intermediates for the convenient synthesis of many pharmaceutical and biologically active compounds. Fluoroorganics play a vital role in the design of very effective therapeutics due to significant enhancenment in their lipophilicity, bioavailability, and fast uptake by the presence of fluorine in these molecules. Herein, we report an efficient one-pot synthesis of trifluoromethylated arylpropanoic acids, indanones, and dihydrocoumarins using Friedel−Crafts alkylation or tandem Friedel−Crafts alkylation−cycloacylation of arenes/phenols with 2-(trifluoromethyl)acrylic acid under superacidic conditions using trifluoromethanesulfonic acid. The results have been rationalized by the structure energy calculations of the involved reaction intermediates using ab initio theoretical methods.

Solid hydrogen peroxide complexes based on poly(N-vinylpyrrolidone) and poly(4-vinylpyridine) were prepared and used as solid hydroxylating reagents. These solid hydrogen peroxide equivalents are found to be much safer, convenient and efficient reagent systems for the ipso-hydroxylation of arylboronic acids to the corresponding phenols in high yields at a faster rate. The versatility of the reagents has been further expanded for the one-pot synthesis of halophenols. Density functional theory calculations were carried out on hydrogen peroxide complexes of N-ethylpyrrolidone and 4-ethylpyridine as models to get a better understanding of structure and behavior of hydrogen peroxide complexes of the polymers poly(N-vinylpyrrolidone) and poly(4-vinylpyridine) compared to aqueous hydrogen peroxide.

Structures as well as 15N and 19F NMR chemical shifts of a series of fluoroammonium ions were studied by ab initio/GIAO-SCF, GIAO-MP2 and GIAO-CCSD(T) methods. Calculated 15N and 19F NMR chemical shifts correlate well with the experimental data. The relative stabilities as well as the charge of the central nitrogen atom of fluoro-substituted tetrahedral ammonium ions were found to increase linearly with the increasing number of fluorine substituents due to their strong electron-withdrawing inductive effect. Similarly the magnitude of 15N NMR chemical shifts also increase linearly with the increasing number of fluorine substituents in accord with the strong deshielding effect of fluorine. Structures as well as 15N and 19F NMR chemical shifts of yet experimentally unknown fluoroammonium dications were also computed.

a,a-Dicyclopropylcyclobutylmethyl cation is a unique cyclobutylmethyl cation, which is stabilized by neighboring cyclopropyl groups. It is persistent up to -40 °C in super-acidic medium. The primary and secondary cyclobutylmethyl cations, however, are still elusive species. a,a-Dicyclo-propylcyclobutylmethyl cation adopts a bisected conformation as shown by the variable temperature dynamic 13 C NMR spectroscopy, in conjunction with density functional theoretical (DFT) calculations. DFT calculations for a,a-dimethylcyclobutylmethyl cation, and endo- and exo- α-methylcyclobutylmethyl cations show that these carbocations also exist as bisected conformers. Primary cyclobutylmethyl cation, on the other hand, spontaneously collapses to cyclopentyl cation at B3LYP/6-311+G* level.

BF3.2CF3CH2OH complex was found to be a very effective superacidic catalyst comparable in acid strength to at least that of 100% anhydrous sulfuric acid for various acid-catalyzed organic transformations such as isomerizations, rearrangements, ionic hydrogenation of various ketones, and aromatics with triethylsilane and nitration of aromatics with metal nitrate. Studies of the pivalaldehyde-methyl isopropyl ketone rearrangement and the benzopinacol to phenanthrene transformation suggest that the complex has an acidity comparable to that of 100% anhydrous sulfuric acid. The structure and properties of the 1:2 boron trifluoride-trifluoroethanol complex have been further studied using NMR (1H, 13C, 19F, 11B) and DFT calculations at the B3LYP/6-311++G//B3LYP/6-31G level.

N-Halosuccinimides (NXS, 1) are efficiently activated in trifluoromethanesulfonic acid and BF(3)-H(2)O, allowing the halogenations of deactivated aromatics. Because BF(3)-H(2)O is more economic, easy to prepare, nonoxidizing, and offers sufficiently high acidity (-H(0) approximately 12, only slightly lower than that of trifluoromethanesulfonic acid), an efficient new electrophilic reagent combination of NXS/BF(3)-H(2)O has been developed. DFT calculations at the B3LYP/6-311++G//B3LYP/6-31G level suggest that protonated N-halosuccinimides undergo further protosolvation at higher acidities to reactive superelectrophilic species capable either in the transfer of X(+) from the protonated forms of NXS to the aromatic substrate or in forming a highly reactive and solvated X(+) which would readily react with the aromatic substrates. Structural aspects of the BF(3)-H(2)O complex have also been investigated.

Good linear correlations between GIAO-MP2 calculated 11B NMR chemical shifts of boronium−onium cations 1a−h and 13C NMR chemical shift of the corresponding isoelectronic carbonium−onium dications 2a−h as well as between 27Al NMR chemical shifts of the alonium−onium cations 3a−h and the 29Si NMR chemical shifts of the corresponding isoelectronic siliconium−onium dications 4a−h were found. The close relationship demonstrates that the same factors that determine the chemical shifts of the boron and aluminum nuclei also govern the chemical shifts of the carbon and silicon nuclei, respectively, within the hypercoordinate onium compounds. On the other hand, no correlation exists between 13C NMR chemical shifts of carbonium−onium dications 2a−h and the 29Si NMR chemical shifts of the corresponding siliconium−onium dications 4a−h. Furthermore, no correlation was found between 11B NMR chemical shifts of boronium−onium cations 1a−h and 27Al NMR chemical shifts of the corresponding alonium−onium cations 3a−h.

Structures of B2H2n2+ dications (n = 1−4) were investigated at the QCISD(T)/6-311G** level of theory. Thermodynamic and kinetic stabilities of the dications were also estimated. Although deprotonations of the dications are exothermic (except the dication B2H22+), they show considerable kinetic barriers. The charge distributions and Wiberg bond indices were calculated by the NBO method. 11B NMR chemical shifts were also calculated by GIAO-MP2 and GIAO-DFT methods.