Reaction of diketene with 5-phenyltetrazole (I) gave rise to 2-acetonyl-5-phenyl-1, 3, 4-oxadiazole (VII), and 3-(5-phenyl-1, 3, 4-oxadiazol-2-yl)-2, 6-dimethyl-4-pyrone (VIII). On the other hand, when this reaction was carried out in acetic acid with reflux, 2-methyl-5-phenyl-1, 3, 4-oxadiazole (IX) and 1, 1-diacetyl-2-benzoylhydrazine (X) were obtained. Reaction of diketene with 5-aminotetrazole (III) resulted in the formation of 7-methyltetrazolo [1, 5-a] pyrimidin-5 (8H)-one (XI).