Abstract. The title compounds pyridazino [6,1-b]quinazolinones were prepared in five steps from succinic anhydride in good yield without the need for chromatography. The barrier to rotation around the N-N bond and concurrent ring-inversion in 7 and 15, was so low at room temperature by comparison with 3-diacylaminoquinazolinone. The preferred geometries have been determined by a Hartree-Fock and Density Function Theory calculation [RHF/6-31G**(d), B3LYP/6-311G**(d)].