Hyperconjugation effect on diene reactivity in 1-methyltetrazolo[5,1-a]isoindole-derived amides and thioamides

Optimized synthesis of 1-methyltetrazolo5,1-a]isoindole-derived amides and thioamides was elaborated. Based on ¹³C NMR spectroscopy and X-Ray diffraction studies data, it was proposed that zwitterionic resonance structures contributed significantly to the structure of these compounds. Geometry optimization was performed in vacuo using m06-2x/cc-pvtz method taking into account polarizing effect of environment (PCM model) and specific intermolecular interactions. Electronic density distribution in these molecules was analyzed using NBO method. Using Δ(HOMO_diene–LUMO_dienophile) for amides and thioamides in vacuo and in a protic solvent, possibility of Diels–Alder reaction was evaluated. Energies of π-π conjugation and n→σ* hyperconjugation for the amide derivative were estimated in vacuo, aprotic and protic solvents.