Pyridine Derivatives as Insecticides. Part 7. Synthesis, Characterization and Insecticidal Activity of Some New 1-Amino-N-substituted-6,7,8,9-tetrahydro-thieno[2,3-c]isoquinoline-2-carboxamides and Their 1-(1-Pyrrolyl) Analogues

One of the main causes propelling the development of new insecticidal active agents is the exponential rise in resistance to traditional chemical pesticides. One approach to solving this issue is to investigate novel types of insecticidal substances with unique ones. In this paper, various series of 6,7,8,9-tetrahydrothieno[2,3-c]isoquinolines were synthesized starting from 7-acetyl-4-cyano-1,6-dimethyl-6-hydroxy-8-aryl-5,6,7,8-tetrahydroisoquinoline-3(2H)-thiones 2a–c. Thus, compounds 2a–c were reacted with some halogeno reagents, namely: N-aryl-2-chloroacetamides 3a–f, N-(naphthalen-2-yl)-2-chloroacetamide (3g), N-(4-phenylthiazol-2-yl)-2-chloroacetamide (3h), and N-(benzthiazol-2-yl)-2-chloroacetamide (3i), in the presence of anhydrous sodium carbonate, to give the target compounds, 1-amino-N-substituted-6,7,8,9-tetrahydrothieno[2,3-c]isoquinoline-2-carboxamides 4a–i, 5a–c, 6, and 7, respectively. Compounds 4f,g,i, 6, and 7 underwent a Paal–Knorr reaction upon treatment with 2,5-dimethoxytetrahydrofuran in boiling glacial acetic acid, to give the corresponding 1-(1-pyrrolyl)-6,7,8,9-tetrahydrothieno[2,3-c]isoquinoline-2-carboxamide derivatives 8f,g,i, 9, and 10. Using elemental and spectral investigations, the structures of every chemical were described. The insecticidal activity of a majority of recently synthesized compounds against the nymphs and adults of A. craccivora was assessed, and encouraging findings were found.