Attempted synthesis of spiro [3H-Indole-3,5'-4'H] [1,3,4] oxadiazole

Reaction of [1,2-dihydro-2-oxo-3H-indol-3-ylidene] carboxylic acid hydrazides 10-27 with acetic anhydride did not afford the expected spiro [3H-indole-3,5'-4'H][1,3,4]oxadizole]-2[1H]-ones, but instead, transacylation was observed. An explanation for this experimental finding was disclosed. IR, 1H-NMR and MS spectral data of the prepared compounds were given and their electron impact fragmentation were interpreted