Phthalhydrazide is a reagent used in the synthesis of various pyrazolophthalazine derivatives is and used in medicine double hydrazine phthalocyanine work intermediates.
Ramin Ghahremanzadeh; Somayyeh Ahadi; Maryam Sayyafi; Ayoob Bazgir. Reaction of phthalhydrazide and acetylenedicarboxylates in the presence of N-heterocycles: an efficient synthesis of phthalazine derivatives. Tetrahedron Letters. 2008, 49 (29-30), 4479-4482.
Ludwig Bauer; Aboo Shoeb; Vincent C. Agwada. The Reaction of 2- and 4- Vinylpyridine with Hydroxylamine, Benzyloxyamine, and Phthalhydrazide. J. Org. Chem. 1962, 27 (9), 3153-3155.
Precursor, by oxidation, e.g. with lead(IV) acetate or t-butyl hypochlorite, of the reactive azadienophile, phthalazine-1,4-dione: J. Am. Chem. Soc., 84, 966 (1962); J. Org. Chem., 25, 1724 (1960); 27, 1115 (1962); 31, 3862 (1966), which also undergoes (last ref.) a (2 + 2)-cycloaddition reaction with indene.