Molecular mechanism of Hetero Diels-Alder reactions between (E)-1,1,1-trifluoro-3-nitrobut-2-enes and enamine systems in the light of Molecular Electron Density Theory

Abstract

The molecular mechanism of the reaction of (E)-1,1,1-trifluoro-3-nitrobut-2-ene 1 with 3,3-dimethyl-2-morpholinobutene 2 has been studied within the Molecular Electron Density Theory (MEDT). This theoretical study confirm the possibility of the formation of zwitterionic structures in the first reaction stage. Interestingly, that localized zwitterions are however not common intermediates for identified in the postreaction mixture products. The further Bonding Evolution Theory (BET) study show, that the key, HDA reaction takes place in one-step but in a non-concerted manner since three stages are clearly identified. First the C5-C6 double bond breaks, then the C1-C2 bond breaks, and in the last phase we observed the formation of the C1-C6 single bond and V(C2) and V' (C2) pseudoradical centers in Z1 molecule. In turn, the molecular mechanism of the conversion of zwitterion Z1 to product 3 can be divided also in three groups in which we observed the disappearance of the two pseudoradical centers and formation O4-C5 single and C3-N3 double bonds, respectively.

Keywords: Bonding evolution theory; Hetero diels-alder reaction; Molecular electron density theory; Molecular mechanism; Nitroalkenes.