Tetracyclic Heteroaromatic Systems-Synthesis of Ethoxycarbonylphenylpyrido[3',2':5,6] Thiopyranoquinolines

7-benzylideneamino-5H-thiochromeno[2,3-b]pyridin-5-ones and 9-benzylideneamino-5H-thio- chromeno[2,3-b]pyridin-5-ones, on reaction with ethyl pyruvate to afford 1-ethoxycarbonyl-3-phenyl-12H- pyrido[3',2':5,6]thiopyrano[3,2-f]quinoline-12-ones and 4-ethoxycarbonyl-2-phenyl-7H- pyrido[3',2':5,6]thiopyrano[3,2-h]quinoline-7-ones respectively by the two different methods. These products were precipitated by addition of ethanol, water (1:1), were purified by recrystalizing from appropriate solvents and were characterized from their IR, 1H-NMR, mass spectra and elemental analysis data.