Superacid-catalyzed reactions of cinnamic acids and the role of superelectrophiles

The chemistry of cinnamic acids and related compounds has been studied. In superacid-catalyzed reactions with arenes, two competing reaction mechanisms are proposed. Both mechanisms involve the formation of dicationic intermediates (superelectrophiles), and the reactions can lead to either chalcone-type products or indanone products. The direct observation of a dicationic species (by low-temperature (13)C NMR) is reported. We provide clear evidence that protonated carboxylic acid groups (or the corresponding acyl cation) can enhance the reactivity of an adjacent electrophilic center. Triflic acid is also found to be an effective acid catalyst for the direct synthesis of some electron-deficient chalcones and heterocyclic chalcones from cinnnamic acids.     

Superacid-catalyzed reactions of olefinic pyrazines: an example of anti-Markovnikov addition involving superelectrophiles

[reaction: see text] Olefinic pyrazines are found to react with benzene in CF3SO3H and give anti-Markovnikov-type addition products. We propose that this is caused by two effects: destabilization of the carbocationic intermediates that would lead to Markovnikov-type products and the generation of a considerable amount of positive charge at the terminal carbon of the olefinic groups. This suggests that acid-catalyzed addition reactions can give anti-Markovnikov-type products when a multiply charged (i.e., superelectrophilic) group is adjacent to the olefinic site.     

Superacid-catalyzed Friedel-Crafts cyclization of unactivated alkenes

Trifluoromethanesulfonimide is an effective catalyst for Friedel-Crafts cyclizations of simple, nonpolarized alkenes with a variety of pendant arenes. A catalyst loading of 0.5 - 1.0 mol % effects clean cyclization to form 5- to 7-membered carbocycles with generally short reaction times and good to excellent yields under reflux or microwave heating.     

Reactivity of isomeric pyridinecarboxaldehydes in catalyic hydrogenation

It has been established by a quantum-chemical method (CNDO/2) that there are two possible mechanisms occurring in the vapor phase hydrogenation of 2-, 3-, and 4-pyridinecarboxaldehydes in the presence of a copper-chromium catalyst at 180-300°C. One of these involves a donor-acceptor interaction of aldehyde with catalyst and the addition of hydrogen to the carbon atom of the carbonyl group at the first stage. The second possible mechanism is the synchronous addition of hydrogen to the carbon and oxygen of the carbonyl group of a weakly bound a aldehyde molecule with an unchanged electronic structure.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1082–1086, August, 1994.     

Condensation products of Betti base and pyridinecarboxaldehydes

Russian Chemical Bulletin - Previously unknown condensation products were obtained by the reaction of the racemic Betti base with 2-, 3- and 4-pyridinecarboxaldehydes. It was established that they...     

Superacid-catalyzed intramolecular cyclization reaction of arylcyanopropionate: geminal substitution effect on superelectrophilicity

We present superacid-catalyzed intramolecular cyclization reactions of arylcyanopropionates to give cyclized five- and six-membered beta-enamino esters in moderate to high yields. Known intramolecular ring-closing reactions of protonated nitrile to aromatic carbon atom are limited to the 6-membered case. Interestingly, a significant synergistic increase of reactivity of the cyano functionality was observed, and the cyano nitrogen atom was converted into an amino group, when an ester group was present in a geminal arrangement. Deuterium exchange experiments excluded the involvement of deprotonation of the alpha-proton in the cyclization process. The acidity dependence of the cyclization reactions and (13)C NMR studies of a model compound, methyl cyanoacetate, in various acidic media were consistent with the involvement of the O, N-diprotonated dication of methyl cyanoacetate, a distonic dication, in strong acid, and this is considered to be the de facto electrophile in the present cyclization reaction of arylcyanopropionates.     

Conjugates of several lupane,oleanane, and ursane triterpenoids with the antituberculosis drug isoniazid and pyridinecarboxaldehydes

Conjugates of betulinic, oleanolic, ursolic, and glycyrrhetic acids and several of their derivatives with the antituberculosis drug isoniazid and 3- and 4-pyridinecarboxaldehydes were synthesized.     

A Superacid-catalyzed Synthesis of Fluorescent Covalent Triazine Based Framework Containing Perylene Tetraanhydride Bisimide for Sensing to O-nitrophenol with Ultrahigh Sensitivity

Abstract

A mesoporous covalent triazine framework, PCPDI, was synthesized via an aromatic nitrile trimerization reaction of N,N′-di(4-cyanphenyl)- 3,4,9,10-tetracarboxydiimide (CPDI) by CF₃SO₃H catalyzed at 40?°C and this method avoids the use of noble metal catalyzers or high temperature reaction. PCPDI exhibits high thermal stability and strong fluorescence. The PCPDI shows ultrahigh sensitivity to tracing o-nitrophenol in chloroform with K_SV constant of 1.74?×?10⁵ L mol^?1 and detection limit (LOD) of 1.72?×?10^?11?mol L^?1.     

Electrocatalytic reactions: anion radical cyclobutanation reactions and electrogenerated base reactions

Intermolecular anion radical [2+2] cyclobutanation reactions have been observed between vinyl sulfones and vinyl/propenyl ketones. The products are novel and formed electrocatalytically, although yields are at best modest (11-45%). Competing mechanisms are discussed. Additionally, the electrochemical reduction of vinyl alkyl sulfones in acetonitrile leads to near quantitative formation of cyanomethylation product cyano-sulfones. The single step approach has electrocatalytic factors in excess of thirty.     

Hamiltonian dynamics of chemical reactions. Consecutive first-order reactions and reactions possessing one autocatalytic intermediate

A recently proposed Hamiltonian approach to phenomenological chemical kinetics [T. Georgian and G.L. Findley, Int. J. Quantum Chem., Quantum Biol. Symp. 10 , 331 (1983); T. Georgian, J.M. Halpin, and G.L. Findley, Int. J. Quantum Chem., Quantum Biol. Symp. 11 , 347 (1984)] is applied to all consecutive first-order, single-step reactions, and to all reactions possessing one autocatalytic intermediate. The reaction Hamiltonians presented are shown to be consistent with the phenomenological rate equations and the relationship between reaction form and the form of the reaction potential is discussed. In particular, we show: (1) that the interaction between consecutive reactions manifests itself as a coupling term in the reaction potential, a term which may be eliminated via transition to “normal reaction coordinates” for the chemical system; and (2) that coupled sets of autocatalytic reactions give rise to coupling terms in the reaction Hamiltonian which are characteristic of the reaction mechanism.     

Electroprotic reactions

Reactions involving the coupled transfer of electrons and protons are called electroprotic reactions. In this article we briefly describe some of our experiences with electroprotic reaction as a tool for executing interesting chemical transformations.     

Pseudo-zero-order reactions

Reactions at the very first instant of their life, i.e., short after their start, follow a pseudo-zero-order kinetics. The initial rate method studying the very first instants of a reaction, which, i.e., can last hours, if k is in days, when it is applied to the integrated rate laws, allows to approximate any kinetics with a pseudo-zero-order. This kind of kinetics allows, nevertheless to derive valuable information about the characteristics of a reaction, which can be obtained by running the reaction at different initial concentrations. This could spare a lot of time required normally for collecting kinetic data over three or more half-lives.