Wittig Olefination with Novel 1,2,4-Oxadiazole-Substituted Triphenylphosphonium Ylides

This work explores, for the first time, the Wittig reaction of a novel class of stabilized ylides, 5-[(triphenylphosphoranylidene)methyl]-1,2,4-oxadiazole hydrochlorides. The reaction of 3-aryl-5-[(triphenylphosphoranylidene)methyl]-1,2,4-oxadiazolium salts with a range of aromatic and heterocyclic aldehydes proceeds regioselectively, affording (E)-5-styryl- and (E)-5-heteroarylvinyl-1,2,4-oxadiazoles in yields of up to 84%. Fourteen olefination products were fully characterized by 1H and 13C NMR spectroscopy and mass spectrometry. The compounds were screened for antibacterial and antioxidant activity, though none was detected. The developed method provides a versatile and promising route for the synthesis of linear π-conjugated systems based on the 1,2,4-oxadiazole scaffold, which are of interest for the development of fluorescent materials, ligands in coordination chemistry, and biologically active compounds.