Attempted monoalkylation of 4-amino-phthalimide using triethylorthoformate [77] gave a mixture of mono- and dialkylated products 13 that were difficult to separate. Gould-Jacobs quinolone synthesis with thermal cyclization of 1 exclusively gave the linear product 2. Careful work-up of the mother-liquors gave no indication of any angular cyclization product. 2 was dialkylated using trialkyl phosphates to 3 and hydrolized either to the acids 4 or 5b. 5b could not be converted to the cyclic anhydride by treatment with acetic anhydride but the imid 6 was obtained from 5b by heating with urea in nitrobenzene [74]. Hofmann-degradation of the imid 6 gave a 1:3 mixture of the isomers 8 and 9 and the structures were assigned using the increment-based program for the assignment of aromatic protons and carbons. This DOS-program is included in this electronic publication. The ¹³C-assignment was in agreement with the published spectra of pyridone-derivatives [78,79]. Changing the temperature for the Hofman-degradation between 0° and 50° did not change the ratio of 8 : 9. Cyclization of 9 using formamidine acetate and urea gave 11 and 12 respectively. Furthermore, cyclization of 4a using hydrizine hydrate gave 7, a derivative of the novel 1H-pyrido[2,3-f]phthalazine ring system.

 The annelated quinolones were tested for their antibacterial activity. In knowledge of known structure activity relationships of quinolones it was no surprise, that the antibacterial activity was much lower that those of the standards like norfloxacin or ciprofloxacin.