Expeditious synthesis of 1,3,4-oxadiazole derivatives via sydnones

Abstract

The clean cyclization of chalcones (1a-c/2a-c) with hydrazine hydrate under microwave irradiation afforded pyrazolines derivatised with sydnone (3d-i/4d-i), which underwent 1,3-dipolar cyclo-addition with acetic an-hydride to form pyrazolines appended with 1,3,4-oxadiazoles (5g-l/6g-l). The newly synthesized compounds were confirmed by spectral and elemental analyses. In comparison to classical heating, the results indicate that microwave irradiation affords higher yields, shorter reaction times (4-12 min) and cleaner reactions.