A novel preparative method for 1‐alkyl‐1,4‐dihydro‐4‐oxo‐3‐quinolinecarboxylic acids was developed. The key process is the cyclization of N‐alkylanilinomethylenemalonales, which was effected successfully in the presence of polyphosphoric acid, polyphosphate ester, boron tri‐fluoride or a mixture of acetic anhydride and sulfuric acid. With phosphorus oxychloride, N‐alkylanilinomethylenemalonates yielded 1‐alkyl‐4‐chloro‐3‐carbethoxyquinolinium salts which were hydrolyzed readily to ethyl 1‐alkyl‐1,4‐dihydro‐4‐oxo‐3‐quinolineearboxylates or their acids. By means of this novel method several new 1‐alkyl‐1,4‐dihydro‐4‐oxo‐3‐quinolineearboxylic acids were prepared.

Die substituierten Aniline (I) werden bei längerem Erhitzen in Alkohol in Gegenwart von Raney‐Nickel ausschließlich zu sekundären Anilinen (II) alkyliert.