This work includes the synthesis of ten heterocyclic compounds (3a-i and 4) containing pyrimidine moiety incorporated in their structures. Structure characterizations of these compounds were performed by using elemental and spectroscopic analyses. Their toxicity as potential insecticidal agents against the adults and nymphs of cowpea Aphid, Aphis craccivora Koch was evaluated. The results of this toxicological activity test revealed that a reasonable number of these compounds possess excellent toxicological activity against cowpea aphids such as compounds (3d), (3c), and (3b) with LC50 values 0.0125, 0.0134, and 0.0383 ppm, respectively. The toxicological activities of the rest of the tested compounds ranged from good to moderate against the same insects.

In examining for unique insecticidal agents, two derivatives namely, 2-((3-cyano-4,6-distyrylpyridin-2-yl)thio)-N-(4-nitrophenyl)acetamide (2) and 3-amino-N-(4-nitrophenyl)-4,6-distyrylthieno[2,3-b]pyridine-2-carboxamide (3) were synthesized from distyrylpyridine-2-thione (1). The new compounds were structurally clarified by spectral and elemental analysis data. The insecticidal activity of these compounds were carried out against cowpea aphid, Aphis craccivora Koch. It is demonstrated that the compounds 2 and 3 have noteworthy insecticidal activity against nymphs of cowpea aphid with LC50 values of 0.025-0.027 ppm and 0.005-0.006 ppm after 24 h and 48 h of treatment, respectively. Also, the compounds 2 and 3 have noteworthy insecticidal activity against adults of cowpea aphid with LC50 values of 0.112-0.129 ppm and 0.014-0.015 ppm after 24 h and 48 h of treatment, respectively, that were comparable to that of the control acetamiprid.

Starting from 3-cyano-4,6-distyrylpyridin-2(1H)-thione (1), the compound N-(4-chlorophenyl)-2-((3-cyano-4,6-distyrylpyridin-2-yl)thio)acetamide (2) was prepared. Compound (2) underwent cyclization upon heating in ethanolic sodium ethoxide solution to give the corresponding cyclized form 3-amino-N-(4-chlorophenyl)-4,6-distyrylthieno[2,3-b]pyridine-2-carboxamide (3). The elemental analyses and spectroscopic data of compounds (2) and (3) are in agreement with their proposed structures. Their insecticidal activity against cowpea aphid, Aphis craccivora Koch, was studied. The results of insecticidal activity for compounds (2) and (3) against the nymphs and the adults of the tested insects exhibited that compounds (2) and (3) have a higher insecticidal activity than that of acetamiprid, a reference insecticide, after 24 h of treatment.