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3- 6,7,6]naphthyridine-2(1H)-thione (3a) and 3-cyano-6-methyl-4-(2'-thienyl)-5,6,7,8tetrahydro[1,6]naphthyridine-2(1H)-thione (3b) were reacted with a-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.

2-Bromo-4-fluoroaniline (1) was condensed with ethyl 2-cyano-3-ethoxyacrylate (2) in ethanol to afford 3, which upon refluxing in paraffin oil at 250°C gave 8-bromo-3-cyano-6-fluoroquinoline-4(1H)-one (4). Then, compound 4 was taken as a versatile building block that allows the synthesis of thieno[3,2-c]quinoline, pyrrolo[3,2-c]quinoline, and N-methylpyrrolo[3,2-c]quinoline systems. The newly synthesized compounds and their derivatives were characterized by elemental analysis and spectroscopy (IR, (1)H NMR, (13)C NMR, and mass). Furthermore, some of these synthesized compounds were screened for their biological activities against various pathogenic bacterial and fungal strains. Our results demonstrate that most of the synthesized compounds possess a significant broad antibacterial activity against all strains of both gram-positive and gram-negative bacteria. In addition, compound 5 showed remarkable antifungal activity.

A one-step synthesis of [1,6]naphthyridine-2(1H)-thione (3a), pyrano[3,4-b]pyridine-2(1H)- thione (3b), thiopyrano[3,4-b]pyridine-2(1H)-thione (3c) and 6-oxoquinoline-2(1H)-thione (3d) through the reaction of benzylidene-cyanothioacetamide (1) with cyclic ketones 2a−d is described. The reaction of 3a−d with organyl chlorides yielded the 2-alkylthio-3-cyanopyridines 4a−p which upon refluxing in ethanolic sodium ethoxide afforded the thieno[2,3-b]pyridine derivatives 5a−n. Some of the synthesized compounds were screened for the activity against bacteria and fungi.

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