Treatment of properly 6-(substituted aryl)-5-acetyl-4-chloro- and 4-methylthio-3(2H)-pyridazinones with SnCl2/HCl afforded pyridazino[4,3-c] quinolinones 9 and 10, whereas the pyridazino[4,5-b] quinolinone derivative 6 was prepared by reduction of the 5-acetyl-4-anilino-6-phenyl-3(2H)-pyridazinone with sodium borohydride, followed by dehydration with polyphosphoric acid (PPA).