Heterocycles [h]Fused on 4-Oxoquinoline-3-carboxylic Acid, II. A Facile Synthesis of Some 2,7-Dioxo[1,4]thiazin[2,3-h]quinoline-8-carboxylic Acids

Model tetrahydro [1,4]thiazino [2,3-h]quinoline-8-carboxylic acids (7ac) are synthesized via reductive lactamisation, using sodium dithionite, of the respective 7-[(carboxyalkyl)thio]-8-nitro-1,4-dihydroquinolines (5a-c).The latter compounds are made accessible via the reaction of 7-chloro-1-cyclopropyl-6flouro-8-nitro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (4) with each of αmercaptoacetic, α-mercaptopropionic and α-mercaptosuccinic acids in aqueous ethanol and triethylamine.The suggested structures of 5a-c and 7a-c are supported by microanalytical and spectral (IR, MS, NMR) data.