Synthesis of new coumarin based acetohydrazones and their correspounding oxadiazoles and oxadiazolines and the investigation of their keto-enol and/or amide–iminol tautomerization

Abstract

Abstract Here we report the synthesis, structural identification and tautomeric behavior of new series of coumarin based hydrazide-hydrazones and their 1,3,4-oxadiazole and oxadiazoline derivatives. In fact The synthesis of 1,3,4-oxadiazoles and oxadiazoline bearing coumarin ring was intended for deducing the isomerization-tautomerization of their hydrazone precursors. Convectional synthesis of several coumarin-oxadiazole derivatives from starting compound, 4-Methylcoumarinyl-7-yl-oxymethyl acetic acid hydrazide has been accomplished. Both types of hydrogens: the hydrazone N-H and methylene protons can take part to tautomeric isomerization equilibria. According to the nmr investigation we found that the keto-enol tautomerization is more favored than amide-iminol. This concept was further established by converting the hydrazones to the corresponding 1,3,4-oxadiazoles and oxadiazolines according to the modified procedures.