Abstract A modified procedure was developed for the synthesis of 5, 6, 7, 8, 13, 13a- hexahydrophthalazino [1, 2-b] quinazoline-5, 8-dione and 6-amino-5, 6, 6a, 11- tetrahydroisoindolo [2, 1-a] quinazoline-5, 11-dione from o-formylbenzoic acid and anthranilic acid hydrazide. The mechanism of the transformation is suggested, some reactions were studied, and new derivatives of these compounds were synthesized. ...