Chemistry of Substituted Quinolines: Thieno[2,3-b] and Thiopyrano[2,3-b]quinolines

Abstract

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 POCl ₃ 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, ¹ H NMR, and mass spectral data.

Keywords:

• 3-formyl-2-chloroquinolines
• 3-formyl-2-mercaptoquinolines
• 3-formyl-(quinolin-2-yl)thio acetic acids
• methyl thieno[2,3-b]quinoline-2-carboxylates
• thieno[2,3-b]quinolines
• thiopyrano[2,3-b]quinolines

Acknowledgments

The authors are thankful to the Chairman, Department of PG Studies and Research in Chemistry, School of Chemical Sciences, Kuvempu University, for providing laboratory facilities. The authors are also thankful to the Convenor, NMR Research Center, Indian Institute of Science, Bangalore, for spectral data.