Synthesis Characterization and Stereostructures of the Pyridazino[6,1-b]Quinazolinones

The title compounds pyridazino[6,1-b]quinazolinones wereprepared in five steps from succinic anhydride in good yield withoutthe need for chromatography. The barrier to rotation around the N-Nbond and concurrent ring-inversion in 7 and 15, was so low at roomtemperature by comparison with 3-diacylaminoquinazolinone. Thepreferred geometries have been determined by a Hartree-Fock andDensity Function Theory calculation [RHF/6-31G**(d), B3LYP/6-311G**(d)].