Synthesis of thieno[2,3-b][1,6]naphthyridines and pyrimido[4′,5′:4,5] thieno[2,3-b][1,6]naphthyridines

Abstract

3-Cyano-6-methyl-5,6,7,8-tetrahydro[1,6]naphthyridine-2(1H)-thione (3a) and 3-cyano-6-methyl-4-(2′-thienyl)-5,6,7,8-tetrahydro[1,6]naphthyridine-2(1H)-thione (3b) were reacted with α-halo compounds to give the intermediates 4a–j which upon refluxing in ethanolic sodium ethoxide afforded the thieno[2,3-b][1,6]naphthyridine derivatives 5a–l. Further annellation of pyridine and pyrimidine rings to the remaining free bond of the fused thiophene ring was achieved, providing tetrahydro-pyrido[2′,3′:4,5]- and -pyrimido[4′,5′:4,5]-thieno[2,3-b][1,6]naphthyridines. Some of the synthesised compounds were screened against different strains of bacteria.