Synthesis, insecticidal evaluation, crystal structure and theoretical calculations of nine/ten-membered carbon bridged neonicotinoid analogues

Neonicotinoid insecticides acting on the insect nicotinic acetylcholine receptors (nAChRs) played an essential role in contemporary pest control. The development of pesticide resistance due to frequent pesticide use had made it increasingly difficult to control pests. In order to explore neonicotinoid insecticide with low cross-resistance and higher potency, larger carbon bridge compounds were constructed by introducing cyclohexanone and cycloheptene in accordance with our previous research. A series of novel neonicotinoid analogues with nine/ten-membered carbon bridge were designed and synthesized, which exhibited a range of insecticidal activities. The results indicated that some the target compounds showed good insecticidal activities against Bemisia tabaci and Aphis gossypii at 100 ppm. In particular, the activities of compounds A1 and A10 reached 90% and 97% respectively, which were similar to that of the control group. Density Functional Theory (DFT) calculations were used to explain the differences in the insecticidal activities of compounds A10, A11, and A12 against Bemisia tabaci. The lowest LUMO energy (ELUMO) of compound A11 (-1.56 eV) might lead to its reduced insecticidal activities. The present study might be meaningful for directing the design of carbon bridged neonicotinoid analogues.