Searching for zwitterionic intermediates in Hetero Diels–Alder reactions between methyl α,p-dinitrocinnamate and vinyl-alkyl ethers

DFT calculations indicate that reactions of methyl α,p-dinitrocinnamate with vinyl-alkyl ethers are of a polar nature, and zwitterionic structures may arise during their course. However, these zwitterions are beyond of cycloadditions paths. On the other hand, HDA reactions of addents carried out according to “two-stage one-step” cycloaddition mechanism. It should be also remarked, that the M062x functional overestimates activation energies.