Synthesis of Pyridothienopyridines and Arylazothienopyridines

Abstract

Treatment of aminothienopyridine 3 with arylidenemalononitrile affords pyridothienopyridine 4. Condensation of 3 with ethyl ethoxymethylene-cyanoacetate affords compound 5, which may be cyclised in diphenyl ether into pyridothienopyridine 6. Thiourea derivative 7 is cyclised using Br₂/ AcOH, and ethyl chloroacetate to afford thiazolothienopyridine 8 and thiazolidinylthienopyridine 9 respectively. Compound 15 is condensed with aromatic aldehydes to give the corresponding arylidenethienopyridines 16a–d. The latter compounds undergo Michael addition with malononitrile to produce pyranothienopyridines 17a–d, Compound 15 was coupled with aromatic diazonium chloride to give the corresponding 2-arylazothienopyridine derivatives 20, but when treated with nitrous acids it dimerised to compound 19.