Exploration of Some Thieno[2,3-b]pyridines, Thieno[3,2-d]pyrimidinones, and Thieno[3,2-d][1,2,3]triazinones as Insecticidal Agents Against Aonidiella aurantii

Objective: Aonidiella aurantii, a highly polyphagous insect pest belonging to the Diaspididae family, is particularly harmful to citrus plants. This pest poses a significant threat to citrus production by infesting both fruits and foliage. In contrast, heterocycle-based compounds have proven to be essential in agrochemicals and pesticides, including fungicides, insecticides/acaricides, and herbicides. In light of this, our research group focused on the synthesis of the title compounds and the evaluation of their insecticidal activity against Aonidiella aurantii. Methods: Three main series of fused heterocyclic compounds, predominantly featuring the ethyl nicotinate scaffold as a substructure, were synthesized in our laboratory. Most of the synthesized compounds were evaluated for their insecticidal activity against the nymphs and adult females of Aonidiella aurantii using the guava leaf dipping technique. Results and Discussion: The reaction of ethyl 4-aryl-5-cyano-2-methyl-6-thioxo-1,6-dihydropyridine-3-carboxylates (Ia–Ib) with N-aryl-2-chloroacetamides, carried out by refluxing in ethanol with a slight excess of anhydrous sodium carbonate, resulted in the formation of the corresponding 3-amino-4-aryl-2-[N-(aryl)carbamoyl]-5-ethoxycarbonyl-6-methylthieno[2,3-b]pyridines (IIa–IIe) in excellent yields. Upon boiling compounds (IIb–IId) with triethyl orthoformate in the presence of acetic anhydride, pyrido[3',2':4,5]thieno[3,2-d]pyrimidinones (IIIb–IIId) were obtained. Treatment of compounds (IIa–IId) with a concentrated solution of sodium nitrite in glacial acetic acid resulted in the formation of pyrido[3',2':4,5]thieno[3,2-d][1,2,3]triazinones (IVa–IVd). The structures of all compounds were confirmed through elemental and spectral analyses. Conclusions: Compounds containing the 4-chlorophenyl scaffold, such as (Ib) and (IIId), exhibited promising results against both nymphs and adult females of Aonidiella aurantii.