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.