Andrzej Barański

Experimental and theoretical studies of Diels–Alder reaction between methyl (Z)-2-nitro-3-(4-nitrophenyl)-2-propenoate and cyclopentadiene

The Diels–Alder reaction between methyl (Z)-2-nitro-3-(4-nitrophenyl)-2-propenoate and cyclopentadiene yields a mixture of carbodiene Diels–Alder adducts. B3LYP/6–31G(d) simulations indicate that the conversion of addends into methyl (1R*,2S*,3S*,4R*)-2-nitro-3-(4-nitrophenyl)-bicyclo[2.2.1]hept-5-ene-2-carboxylate occurs via two-stage heterodiene Diels–Alder reaction and (in a second step) skeleton rearrangement of the primary cycloadduct, whereas the reaction leading to methyl (1R*,2R*,3R*,4R*)-2-nitro-3-(4-nitrophenyl)-bicyclo[2.2.1]hept-5-ene-2-carboxylate is a single-step process.Graphical abstract

Kinetics of the [4+2] cycloaddition of cyclopentadiene with (E)-2-aryl-1-cyano-1-nitroethenes

The electrophilicity of (E)-2-aryl-1-cyano-1-nitroethenes is not sufficient to induce a zwitterionic course of their [4+2] cycloaddition to cyclopentadiene. The one-step mechanism of these reactions is indicated by the activation parameters, and the substituent and solvent effects on the reaction.Graphical Abstract

A B3LYP/6-31G(d) study of Diels-Alder reactions between cyclopentadiene and (E)-2-arylnitroethenes

AbstractThe B3LYP/6-31G(d) simulations of competing CDA and HDA reactions between cyclopentadiene and (E)-2-arylnitroethenes prove that regardless of the medium polarity, the processes leading to respective 5-nitro-6-aryl-bicyclo-[2,2,0]-hept-2-enes 3,4 (paths A and B) should be most favoured, and the more electrophilic (E)-2-(p-nitrophenyl)-nitroethene should be more reactive than the less electrophilic (E)-2-(p-methoxyphenyl)-nitroethene. Asymmetry of the transition complexes on the favoured pathways increases with increase of medium polarity, but not sufficiently to enforce the zwitterionic mechanism. Analysis of competing pathways leading to HDA adducts proves that not all these compounds can be formed directly from the adducts. In particular, on the path C, the initially formed 5-nitro-6-aryl-bicyclo-[2,2,0]-hept-2-enes 3 is converted to 2-phenyl-4-aza-5-oxy-bicyclo-[3,4,0]-nona-3,7-diene N-oxides 5 as a result of a [3.3]-sigmatropic shift. On the paths D–F leading to 2-phenyl-4-aza-5-oxy-bicyclo-[3,4,0]-nonadienes N-oxides 6–8, the reaction proceeds according to a one-step mechanism.

Regio- and stereoselectivity of [2 + 3] cycloaddition of (E)-β-nitrostyrenes to (Z)-C,N-diphenylnitrone in the light of AM1 and AM1/COSMO calculations†

Four isomeric pathways for the [2 + 3] cycloaddition of (E)-β-nitrostyrenes (1a–c) with (Z)-C,N-diphenylnitrone (2) in gas phase and in a dielectric medium corresponding to the relative permittivity of toluene was evaluated in terms of AM1 and AM1/COSMO calculations in order to predict the reaction regio- and stereoselectivity. It was found that in the gas phase reaction takes place in a concerted manner independent of the nitrostyrene used as a dipolarophile and the [2 + 3] cycloadduct formed. The activation barriers obtained indicate that paths B and D (Scheme 1) are favored. The highest activation barrier occurs on the path C. In toluene solution this trend changes and the reaction paths can be ordered in the sequence B > A > D > C. An increase in the polarity of the reaction medium elevates the activation barriers and in some cases changes the reaction mechanism. An increase in the electron-withdrawing character of the substituent in the benzene ring of (E)-β-nitrostyrene speeds up the reaction both in the gas phase and in toluene solution but does not affect the reaction regio- and stereoselectivity. Copyright

Conjugated nitroalkenes in cycloaddition reactions 18*. Regio- and stereoselectivity of (2+3) cycloaddition reactions between gem-chloronitroethene and (Z)-C,N-diarylnitrones

(2+3) Сycloadditions of gem-chloronitroethene to diarylnitrones proceed regiospecifically and lead to stereoisomeric mixtures of 3,4-cis- and 3,4-trans-2,3-diaryl-4-chloro-4-nitroisoxazolidines. The interpretation of the regiospecificity of the reaction based on the theory of reactivity indices shows that its course is determined by an attack of the nucleophilic center at the nitrone oxygen atom to the electrophilic center at the gem-chloronitroethene.

The reaction mechanism of the [2+3] cycloaddition between α-phenylnitroethene and (Z)-C,N-diphenylnitrone in the light of a B3LYP/6-31G(d) computational study

The analysis of reactivity indices suggests the polar nature of the [2+3] cycloaddition of a-phenylnitroethene to (Z)-C,N-diphenylnitrone. Similar conclusions can be drawn from the investigation of the reaction pathways using the B3LYP/6-31g(d) algorithm. This shows that the cycloaddition mechanism depends on the polarity of the reaction medium. A one-step mechanism is followed in the gas phase and toluene in all the theoretically possible pathways. In more polar media (nitromethane, water), a zwitterionic, two-step rather than a one-step mechanism occurs in the pathway leading to 3,4-trans-2,3,5-triphenyl-4-nitroisoxazolidine.Graphical abstract

An experimental and theoretical study of the polar [2+3] cycloaddition reactions between 1-chloro-1-nitroethene and (Z)-C-aryl-N-phenylnitrones

Kinetic studies and B3LYP/6-31g(d) calculations indicate the polar nature of [2+3] cycloadditions between 1-chloro-1-nitroethene to (Z)-C-aryl-N-phenylnitrones. This is clearly confirmed by the activation parameters and the substituent and solvent effects.Graphical abstract

CONJUGATED NITROALKENES IN CYCLOADDITION REACTIONS. 16*. ATYPICAL COURSE OF THE REACTION OF α-NITROSTYRENE WITH (Z)-C,N-DIARYLNITRONES

In order to confirm the results of the quantum-chemical calculations, we studied this reaction at 80°C using a fourfold molar excess of the nitroalkene with toluene as solvent. Under these reaction conditions, the conversion of nitrone 2a reached 100% after 48 h. An HPLC analysis of the resulting mixture indicated the presence of trace amounts of the unreacted nitrostyrene 1 (retention time RT 5.5 min) and significant amounts of -trans-nitrostyrene (7) (RT 6.0 min) as well as two other products with RT 19.4 and 30.1 min, respectively. The latter could be isolated using semipreparative HPLC for the purpose of characterization by IR and H NMR spectroscopy.

Conjugated nitroalkenes in cycloaddition reactions. 17*. Mechanism of (2+3) cycloaddition between (E)-3,3,3-trifluoro-1-nitroprop-1-ene and (Z)-N-methyl-C-phenylnitrone in the light of reactivity indices theory and B3LYP/6-31G* calculations

Analysis of the reactivity indices shows the polar character of the (2+3) cycloaddition between (E)-3,3,3-tri-fluoro-1-nitroprop-1-ene and (Z)-N-methyl-C-phenylnitrone. This is confirmed by exploration of reaction paths by B3LYP/6-31G(d) algorithm. Although the transition complexes involved in the reaction mechanism are considerably asymmetric and polar, the reactions proceed via a one-step mechanism.

Synthesis and Properties of Azoles and Their Derivatives. 52. Periselectivity of [2+3] Cycloaddition of Nitrones to trans-β-Cyanonitroethylene in the Light of FMO Theory

Abstract[2+3] Cycloaddition reaction of nitrones with trans-β-cyanonitroethylene may theoretically lead to regioisomeric nitroisoxazolidines and isomeric oxadiazoles. However, 4- and 5-nitroisoxazolidines were really obtained as only reaction products. Periselectivity of this reaction is rationalized in terms of the FMO theory.