Synthesis of 4-aminothieno[2,3-b] pyridine-5-carboxylie acids

2-Amino-3-cyanothiophenes were reacted with ethyl aminocrotonate in the presence of catalytic amounts of p-toluensulfonic acid. The intermediates 2-N-(3′-ethoxycarbonyl-2′-propenylamino]-3-cyanothiophenes obtained were cyclized with sodium ethoxide to give the desired ethyl 4-aminothieno2,3-b] pyridine-5-carboxylate. Hydrolysis of the latter aminoesters afforded 4-aminothieno2,3-b]pyridine-5-carboxylic acid. The overall yields were about 80%.