Maria Mikulska

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.

Synthesis of nitrones

nitrones, synthesis, hydroxylamines, carbonyl compounds, imines, amines, oximes, nitroso compounds