Azido-tetrazole isomerism in 2,2-dimethyl-1-(1-methyl-1H-tetrazolo [5,1-a]isoindol-5-yl)propan-1-one

For the first time, the tetrazole ring-opening has been observed for tetrazoloisoindoles as an example of azido-tetrazole isomerism. This process was studied in details by HPLC; conditions were found which are optimal for the azido-tetrazole equilibrium. It is shown that the tetrazole ring-opening proceeded with formation of unstable azide intermediate and subsequent extrusion of N-2 molecule. Molecular geometry of the tetrazole form and possible unstable azide forms were calculated using M06-2X/cc-pVTZ method in vacuo and taking into account the effect of polarizing environment, and for azide forms - also taking into account specific intermolecular interactions with solvent. Electron density distribution within the tetrazole form was analyzed using Bader's AIM theory. Resonance structures for azide forms were studied using NBO method. Calculated UV spectra were obtained using CAM-B3LYP/cc-pVTZ methods for all studied molecules. (C) 2019 Elsevier B.V. All rights reserved.