Application of N-Acylbenzotriazoles in the Synthesis of 5-Substituted 2-Ethoxy-1,3,4-oxadiazoles as Building Blocks toward 3,5-Disubstituted 1,3,4-Oxadiazol-2(3H)-ones

5-Substituted-2-ethox-y-1,3,4-oxadiazoks were conveniently prepared through a one-pot sequential N-acylation/dehydrative cyclization between ethyl carbazate and N-acylbenzotriazoles in the presence of Ph3P-I-2 as a dehydrating agent. Subsequent treatment with a stoichiometric amount of alkyl halides (X = Cl, Br, I) enables a rapid access to a variety of 3,5-disubstituted 1,3,4-oxadiazol-2(3H)-ones in good to excellent yields.