Synthesis of halosulfuron-methyl via selective chlorination at 3- and/or 5-position of pyrazole-4-carboxylates

✍ Scribed by Katsushi Morimoto; Toshiaki Sato; Susumu Yamamoto; Hiroshi Takeuchi

• Publisher: Journal of Heterocyclic Chemistry
• Year: 1997
• Tongue: English
• Weight: 301 KB
• Volume: 34
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570340231

✦ Synopsis

Abstract

Reactions of methyl pyrazole‐4‐carboxylates 4b‐d with N‐chlorosuccinimide under heating conditions without a solvent gave methyl 3,5‐dichloro‐1‐methylpyrazole‐4‐carboxylate 4a in good yields. The reaction of 4a with sodium hydrosulfide led to a nucleophilic substitution on the 5‐position regioselectively to afford methyl 3‐chloro‐1‐methyl‐5‐mercaptopyrazole‐4‐carboxylate 6a, which was followed by oxidative chlorination and amination to obtain 3‐chloro‐1‐methyl‐5‐sulfamoylpyrazole‐4‐carboxylate 2a. Finally, the reaction of 2a with phenyl 4,6‐dimethoxypyrimidin‐2‐yl carbamate 7 provided methyl 3‐chloro‐5‐(4,6‐dimethoxypyrimidin‐2‐ylcarbamoylsulfamoyl)‐1‐methylpyrazole‐4‐carboxylate (halosulfuron‐methyl) 1a promising herbicide in com.