Pyridine Derivatives as Insecticides. Part 3. Synthesis, Crystal Structure, and Toxicological Evaluation of Some New Partially Hydrogenated Isoquinolines against <i>Aphis gossypii</i> (<i>Glover</i>, 1887)

Abstract

Three new series of isoquinolines, that is, 7-acetyl-3-acetonylsulfanyl-8-aryl-1,6-dimethyl-6-hydroxy-5,6,7,8-tetrahydroisoquinoline-4-carbonitriles (3a–c); 3-acetonylsulfanyl-8-aryl-1,6-dimethyl-7,8-dihydroisoquinoline-4-carbonitriles (4a–c); and 7-acetyl-8-aryl-1,6-dimethyl-3-ethylsulfanyl-7,8-dihydroisoquinoline-4-carbo-nitriles (6a,b) were carefully synthesized. Also, pyrazoloisoquinoline 7 was used as a precursor for synthesis of 7-ethylsulfanyl-4-phenyl-1-thiocarbamoyl-3,5,9a-trimethyl-3a,4,9,9a-tetrahydro-1H-pyrazolo[3,4-g]isoquinoline-8-carbonitrile (8); 7-benzyl-sulfanyl-4-phenyl-1-thiocarbamoyl-3,5,9a-trimethyl-3a,4,9,9a-tetrahydro-1H-pyrazolo[3,4-g]isoquinoline-8-carbonitrile (9); and 7-ethylsulfanyl-1-(4-oxo-4,5-dihydrothiazol-2-yl)-4-phenyl-3,5,9a-trimethyl-3a,4,9,9a-tetrahydro-1H-pyrazolo[3,4-g]isoquinoline-8-carbonitrile (10). Moreover, the crystal structures of two representative compounds were determined. Eleven new compounds 3a, 4a, 3b, 4b, 3c, 4c, 6a, 6b, 8, 9, and 10 were screneed for their toxicological activity against nymphs and adults of Aphis gossypii by using acetamprid, as a reference. After 24 h of treatment, the bioefficacy results indicate that all tested isoquinolines exhibit toxicological activity that varied from very high to low against nymphs and adults of Aphis gossypii, some compounds showing activity near to that of acetampirid and only one compound which possesses higher activity against nymphs and adults of Aphis gossypii than that of acetampirid itself.