Synthesis and Characterization of New Heterocyclic Compounds Containing Thienylbenzo[h]Quinoline Moiety

In this paper the reaction of 2-(2′-thienylmethylene)-3,4-dihydronaphthalen-2(1H)-one (1) with cyanothioacetamide gave a mixture of 3-cyano-5,6-dihydro-4-(2′-thienyl)-benzo[h]quinolin-2(1H)-thione (2) and the related disulfide 3. Compound 2 was reacted with some halo compounds namely; ethyl chloroacetate, chloroacetamide, chloro(N-(p-chlorophenyl))acetamide, N¹-chloroacetylsulfanilamide, and 2-chloromethyl-1H-benzimidazole to produce a series of 2-(substituted)methylthio-3-cyano-5,6-dihydro-4-(2′-thienyl)benzo[h]quinolines 4a, 4b, 4c, 4d, 4e and 11. Upon heating the latter compounds with sodium ethoxide, they underwent intramolecular Thorpe–Zeigler cyclization to furnish the corresponding 2-(substituted)-3-amino-5,6-dihydro-4-(2′-thienyl)-benzo[h]thieno[2,3-b]quinolines 5a, 5b, 5c, 5d, 5e and 12. (3-Cyano-5,6-dihydro-4-(2′-thienyl)-benzo[h]quinolin-2-ylthio)acethydrazide (8) and the related isomer, 3-amino-5,6-dihydro-4-(2′-thienyl)thieno[2,3-b]benzo[h]quinoline-2-carbohydrazide (9), were also synthesized. Most of the aforementioned compounds were used as key intermediates for synthesizing other benzo[h]quinolines, benzo[h]thieno[2,3-b]quinolines as well as benzo[h]pyrimido[4′,5′:4,5] thieno[2,3-b]quinolines. The structure of all synthesized compounds was confirmed by spectroscopic measurements and analytical analyses.