Experimental and theoretical investigation of new furan and thiophene derivatives containing oxazole, isoxazole, or isothiazole subunits

Herein, we present joint experimental and theoretical studies on newly designed thiophene- or furan-based oxazole, isoxazole, and isothiazole derivatives. Our synthetic approach towards the preparation of target compounds is based on Van Leusen reaction. By following this reaction, oxazoles (1 and 2) containing the pertinent heterocyclic systems were obtained from the reaction of suitable furan or thiophene derivatives with tosylmethyl isocyanide (TOSMIC). Hereby, three ring systems of furan or thiophene, linked to the oxazole rings at their 2- and 5-positions (3 and 4), were also successfully synthesized for the first time. Reaction of the starting materials containing acetyl groups in their 2-position with dimethyl acetal and following the treatment by hydroxylamine hydrochloride, desired isoxazole derivatives (5 and 6), were obtained. Additionally, isothiazole derivatives (7 and 8) were prepared by following the similar approach to the isoxazole synthesis. Whole of these cyclization reactions occurred with good to excellent yields. Structural analyses of the synthesized compounds were performed by appropriate spectroscopic methods (UV-vis, FT-IR, LC-MS, 1H-NMR, 13C-NMR, and elemental analysis). We also carried out theoretical studies for identifying the structure-activity relationship and determining chemical properties of the studied molecules. For this purpose, we obtained information about structural properties (bond lengths, bond angles, dihedral angles, and dipole moments), band gap energies, and spectroscopic characteristics (UV-vis, FT-IR, 1H-NMR, and 13C-NMR) of the target compounds.