Evaluation and Removal of Production Process Constraints in the Synthesis of 3,5-Dibromopyrazole

Multiple methods for the preparation of 3,5-dibromopyrazole are described. While 3,5-dibromopyrazole is readily available on a kilogram scale, an internal demand facilitated the need to expand the vendor pool, with an overall goal of lowering cost. To pursue this goal, we focused on developing synthetic methods in the operating temperature range of −20 to 120 °C to remove production process constraints and explored the option of a continuous flow procedure for regioselective dehalogenation of 3,4,5-tribromopyrazole. An alternative method that started with bromination of pyrazole-3-carboxylate ester, followed by one-pot saponification and decarboxylation, was found to be efficient as well.