Synthesis, spectroscopic, electrochemistry and antioxidant properties of benzofuroxan and 2H-benzimidazole 1,3-dioxide derivatives: Effects of conjugation with electron-acceptor 1,2,3-triazolyl-1,2,4-oxadiazole

• Published in: Journal of molecular structure 2024-09, Vol.1311, p.138420, Article 138420
• Main Authors: Mayer, João C.P., Pereira, Paola C., Sagrilo, Pauline L., Iglesias, Bernardo A., Back, Davi F., da Rocha, Vinícius N., Köhler, Mateus H., Rodrigues, Oscar E.D., Dornelles, Luciano
• Format: Article
• Language: English
• Subjects: 1,2,3-triazoles; 1,2,4-oxadiazoles; Electrochemistry; N-Oxides; Photophysical properties
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2024.138420

•Efficient synthetic combination for the one-pot synthesis of novel benzofuroxan and of 2,2-dimethyl-2H-benzimidazole 1,3-dioxid derivatives: TBTU coupling followed by DBU-promoted cyclization.•UV–vis spectroscopy and electrochemical characterization of the obtained compounds.•In silico prediction of benzofuroxan tautomer stability in NMR: DFT calculation. A series of novel benzofuroxan and of 2,2-dimethyl-2H-benzimidazole 1,3-dioxide derivatives conjugated to the strong electron-withdrawing 1,2,4-oxadiazole ring and to the amide isostere 1,2,3-triazole were synthesized. NHeterocycle-N-oxide-bearing carboxylic acids and 1,2,3-triazole-4-carbamidoximes served as convenient reactants for the obtention of the 1,2,4-oxadiazoles. By employing O-(benzotriazol-1-yl)-N,N,N’,N’-tetramethyluronium tetrafluoroborate (TBTU) as coupling reagent and 1,8-diazabicyclo[5.4.0]undec‑7-ene (DBU) as base in acetonitrile, in a one-pot sequence, at room temperature, products were obtained in generally high yields (64 – 93 %) after two 30 min steps and a simple purification process. NMR spectroscopy, X-Ray diffraction and DFT calculations helped to access the preferential tautomeric structures of selected compounds. UV–Vis spectroscopy revealed characteristic absorption peaks for 1,2,3-triazolyl-1,2,4-oxadiazoles 11aa-be, noteworthy an intramolecular charge transfer (ICT) band around 500–650 nm for benzimidazole-1,3-dioxide derivatives 11ba-be, while low fluorescence quantum yields and Stokes shifts were observed for all compounds. Both oxidation and reduction peaks were observed in Cyclic Voltammetry experiments, including irreversible reduction peaks for all 11aa-be compounds. TD-DFT calculations enabled comprehension of the molecular orbitals participation in the UV–Vis transitions, which depend on the N-oxide, the heterocycles and the substituted phenyl ring. Also, some compounds with electron withdrawing groups (Cl and CF3) also displayed good antioxidant activity in DPPH assays. [Display omitted]