One-pot synthesis of 1,3,4-oxadiazole derivatives was achieved by treatment of 2-((4-(phenoxathiin-2-yl)
phthalazin-1-yl)oxy)acetohydrazide with aromatic aldehydes in the presence of cerium(IV) ammonium
nitrate in dichloromethane. This facile method was confirmed by the cyclization–oxidation reaction of
the corresponding hydrazone by cerium(IV) ammonium nitrate to afford the same 1,3,4-oxadiazoles. Also,
the reaction of 2-((4-(phenoxathiin-2-yl)phthalazin-1-yl)oxy)acetohydrazide with aromatic carboxylic
acids in the presence of cerium(IV) ammonium nitrate in polyethylene glycol afforded 1,3,4-oxadiazole
derivatives. The structural formulae of all products were confirmed and characterized by elemental
analyses and spectral data. Most of the synthesized products were evaluated for their antibacterial and
antifungal activities and showed potent to weak activity.