1,3-dipolar cycloadditions of electron-rich nitrile oxides with some vinylic dipolarophiles

3,4-dihydroisoxazoles are one of the important class of five-membered heterocyclic cores since they are mostly found in the structures of many drug molecules and natural products. Furthermore, most of the five-membered hetecyclic molecules are frequently prepared over 1,3-dipolar cycloaddition reactions which give expected heterocycles rapidly and regioselectively. For these reasons, in the current thesis study, new 3,5-disubstituted isoxazolines have been planned to synthesize via cycloaddition reactions of electron-rich nitrile oxides formed in situ with some electron-deficient vinylic dipolaphiles and to investigate their potential antibacterial properties. In this way, firstly, some p-substituted benzaldoximes bearing EDGs 87 were prepared in excellent yields as one of the precursor compounds. In the meantime, as the second precursor, some vinylic oxadiazole dipolarophiles containing EWGs 90 were prepared in moderate to good yields starting from electron-deficient arylnitriles over three successive steps. The structures of both precursors were characterized by spectroscopic (IR, NMR) and physical data (m.p). Secondly, in situ generated electron-rich nitrile oxides from benzaldoximes 87 were reacted with vinylic dipolarophiles 90 by the aid of NaOCl and Et3N to furnish new 3,5-diaryl substituted isoxazolines 91 in moderate to good yields. The structures of all the target compounds (91a-x) were fully characterized by means of IR, 1H NMR, 13C NMR data Lastly, target compounds (91) has been tested in an antibacterial screening study against ten gram (+) or (-) bacterial strains. As the result of this bioassay, two of the derivatives (91a, 91g) were found to show weak to moderate inhibitory activities against S.aureus and S.epidermidis bacterial strains.