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 ...
