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 CS 2 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, 1 H‐NMR, 13 C‐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.