Reactions of N-isocyaniminotriphenylphosphorane with 2-oxopropyl benzoate (or 2-oxopropyl 4-bromobenzoate) in the presence of 3-phenyl-2-propynoic acid and primary amines proceeded smoothly at room temperature and in neutral conditions to afford sterically congested 1,3,4-oxadiazole derivatives in high yields. The reaction proceeded smoothly and cleanly under mild conditions and no side reactions were observed.