A new mechanistic insight on the molecular mechanisms of the addition reactions of 2-aryl-3-nitro-2H-chromenes to the pyrazole and cyclopentadiene

Abstract

The molecular mechanism of the addition reactions of 2-aryl-3-nitro-2H-chromenes to the pyrazole was evaluated in the framework of the Molecular Electron Density Theory (MEDT) based on the results of the wb97xd/6-311+G(d,p) (PCM) quantumchemical calculations. It was found, that the title reaction is realized under the control of the local interaction between activated electrophilically -carbon atom of the nitrovinyl moiety and the nucleophilically activated nitrogen sp2-atom of the pyrazole. The first reaction stage is the formation of the zwitterionic intermediate, which convert further to final product via [1,4]-proton sigmatropic shift. The reorganization of the electron density was evaluated using the BET technique. The additional calculations in a solvent other than THF and other nitrochromene systems shows, that the proposed mechanism can be treatment as a general for wide range of similar transformations. Obtained results were compared with the analogous study performed for the addition of 2-aryl-3-nitro-2H-chromenes to the pyrazole according to the Diels-Alder scheme, as well as with the reaction between the same nitrochromene and cyclopentadiene.