SYNTHESIS OF HALOSULFURON-METHYL VIA SELECTIVE CHLORINATION AT 3-POSITION AND OR 5-POSITION OF PYRAZOLE-4-CARBOXYLATES/

Reactions of methyl pyrazole-4-carboxylates 4b-d with N-chlorosuccinim ide under heating conditions without a solvent gave methyl 3,5-dichlor o-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-mercapt opyrazole-4-carboxylate 6a, which was followed by oxidative chlorinati on and amination to obtain -chloro-1-methyl-5-sulfamoylpyrazole-4-carb oxylate 2a. Finally, the reaction of 2a with phenyl 4,6-dimethoxypyrim idin-2-yl carbamate 7 provided methyl carbamoylsulfamoyl)-1-methylpyra zole-4-carboxylate (halosulfuron-methyl) 1a promising herbicide in cor n.