Synthesis and Herbicidal Activities of Sulfonylureas Bearing 1,3,4‐Thiadiazole Moiety

In this article, we report the synthesis and herbicidal activities of sulfonylureas bearing the 1,3,4‐thiadiazole moiety. The target compounds 9a , 9b , 9c , 9d , 9e , 9f , 9g , 9h , 9i , 9j , 9k , 9l were synthesized using 2‐hydrazinocarbonyl benzenesulfonamide ( 4 ) and phenyl pyrimidinecarbamates as starting materials. The key intermediate, 2‐(4,5‐dihydro‐5‐thioxo‐1,3,4‐thiadiazol‐2‐yl)benzenesulfonamide ( 5 ), was prepared from 4 and CS₂ via a conventional method or an improved method. The improved method, in which sulfonamido group acts as a directing group for the cyclization reaction, is more concise and efficient. The structures of the target compounds were determined by IR, ¹H‐NMR, ¹³C‐NMR, MS, and elemental analysis. Their herbicidal activities were screened by Petri dish tests and pot tests. As the results, sulfonylureas 9h and 9j inhibited Brassica napus, Amaranthus retroflexus, and Echinochloa crusgalli at the 15 g/ha level, which is at the same level as azimsulfuron. Moreover, the safety tests showed that 9j was safe to wheat at dosage of 60 g/ha and might develop further into a herbicide in wheat field.