Ultrasound-assisted synthesis and preliminary bioactivity of novel 2H-1,2,4-thiadiazolo[2,3-a]pyrimidine derivatives containing fluorine

Eight novel 5,7-disubstituted-2-{5-methyl-3-(4-trifluoromethylphenyl)isoxazol-4-ylcarbonylimino}-2H-1,2,4-thiadiazolo[2,3-a]pyrimidines were synthesized by multi-step reactions in yields 68−85%. Reactions were carried out either by ultrasound irradiation or conventional method, and found it was faster and more efficient under ultrasonic irradiation. Preliminary herbicidal activities against Echinochloa crus-galli, Digitaria sanguinalis and Chenopodium serotinum were also evaluated by flat-utensil method, and the results indicated that the target compounds exhibited significant activities, some were even higher than the control herbicide.