Treatment of isatoic anhydrides with hydrazine hydrate gave 1, 2-bis-(o-aminobenzoyl)-hydrazines (IIa-c). The reaction of IIa, b with ethoxymethylenemalononitrile, ethyl ethoxymethylenecyanoacetate or triethyl orthoformate afforded new 3, 3'-bisquinazoline-4, 4'-diones (IIIa, b and IVa-d) in good yields. On the other hand, the reaction of IIa-c with polyphosphoric acid furnished 2, 5-diaryl-1, 3, 4-oxadiazole derivatives in high yields.
