Design, synthesis, and insecticidal activities of novel 5‐substituted 4, 5‐dihydropyrazolo [1,5‐ a ]quinazoline derivatives

BACKGROUND Chemical pesticides are the main measures for pest control, but have caused growing resistance of pests and brought a series of environmental problems. Development of high‐efficient insecticidal molecules with novel scaffolds is therefore particularly urgent. RESULTS Based on a [5 + 1] annulation reaction with 5‐amino‐1 H ‐phenylpyrazole and dialkyl bromomalonate, 27 novel five‐substituted 4,5‐dihydropyrazolo[1,5‐ a ]quinazolines were designed following the intermediate derivatization method and synthesized. Bioassay results indicated that most of the test compounds displayed good insecticidal activities against Plutella xylostella , Spodoptera frugiperda , and Solenopsis invicta . In particular, the insecticidal activities of compounds 4a , 4f , and 4m against P. xylostella [median lethal concentration (LC 50 ) values ranged from 3.87 to 5.10 mg L −1 ] were comparable to that of indoxacarb (LC 50 = 4.82 mg L −1 ). In addition, compounds 4a and 9e showed similar high insecticidal activities against Spodoptera frugiperda (mortality rate = 79.63% and 72.12%) at 100 mg L −1 , comparable to that of fipronil (mortality rate: 68.44%); compound 9a showed possible delayed toxicity against Solenopsis invicta (mortality rate: 95.66%) after 5 days of treatment at 1.0 mg L −1 . CONCLUSION Due to their high insecticidal activities against P. xylostella , compound 4m , 4a , and 4f could be considered as qualified candidates for novel insecticide. Several other 4,5‐dihydropyrazolo[1,5‐ a ]quinazolines with relatively high bioactivity, such as compounds 9a and 9e , are also worth further optimization as potential insecticide or anticide candidates.