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

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-1 H -pyrazolo[3,4-g]isoquinoline-8-carbonitrile ( 8 ); 7-benzyl-sulfanyl-4-phenyl-1-thiocarbamoyl-3,5,9a-trimethyl-3a,4,9,9a-tetrahydro-1 H -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-1 H -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.