Chemistry of substituted quinolines:: Thieno[2,3-b] and thiopyrano[2,3-b]quinolines

The reaction of 3-formyl-2-chloroquinolines with thioglycolic acid afforded a mixture of uncyclized [(3-formylquinolin-2-yl)thio]acetic acid in a 60-70% yield and cyclized thieno[2,3-b]quinoline-2-carboxylic acids in a 30-40% yield, respectively. The uncyclized compounds on refluxing with POCl3 in various alcoholic media gave [(3-formylquinolin-2-yl)thio]acetates. Further cyclization was achieved by refluxing them with dimethylformamide (DMF) to produce thieno[2,3-b]quinoline derivatives. On the other hand, the reaction of 3-formyl-2-mercaptoquinolines with chloroacetyl chloride in DMF gave 3-chloro-2H-thiopyrano[2,3-b]quinolin-2-ones. The structures of all the newly synthesized compounds were characterized on the basis of elemental analysis, IR, H-1 NMR, and mass spectral data.