Synthesis of novel benzo[6,7]cyclohepta[1,2-b]thieno[3,2-e]pyridines and their bis-analogues linked to different spacers: Approach to a new ring system

The synthesis of benzosuberone-fused heterocyclic derivatives is an increasingly intriguing subject. The current study reports the synthesis of the new ring system benzo[6,7]cyclohepta[1,2-b]thieno[3,2-e]pyridine. At first, new 2-thioxo-2,5,6,7-tetrahydro-1H-benzo[6,7]cyclohepta[1,2-b]pyridine-3-carbonitriles were prepared and taken as versatile precursors for the present study. Afterward, a succession of α-bromoketones were combined with the newly generated synthons in ethanol that also included two equivalents of sodium ethoxide. After 2–3 h of heating at reflux, a novel series of benzo[6,7]cyclohepta[1,2-b]thieno[3,2-e]pyridines was obtained in 86–93% yields. Using a similar protocol, a novel series of benzosuberone-fused bis(thieno[3,2-e]pyridines) linked to different spacers was obtained. Therefore, two pyridine-2(1H)-thiones equivalents were reacted with one equivalent of the respective bis(α-bromoketones) in ethanol containing four equivalents of sodium ethoxide. The reaction mixture was refluxed for 4–6 h to produce the corresponding bis(benzo[6,7]cyclohepta[1,2-b]thieno[3,2-e]pyridines) in 67–76% yields. Both spectral data and elemental analyses were used to elucidate the structure of new products.