Mild and convenient one-pot synthesis of 1,3,4-oxadiazoles

Condensation of carboxylic acids with benzohydrazide in the presence of TBTU afforded diacylhydrazine intermediates that underwent a smooth TsCl-mediated cyclodehydration reaction to afford 2-phenyl-5-substituted-1,3,4-oxadiazoles in good to very good yields.