Highly Regioselective and Practical Synthesis of 5-Bromo-4-chloro-3-nitro-7-azaindole

We report an efficient and highly regiocontrolled route to prepare a functionalized 7-azaindole derivative—5-bromo-4-chloro-3-nitro-7-azaindole—from readily available parent 7-azaindole featuring a highly regioselective bromination of the 4-chloro-3-nitro-7-azaindole intermediate. In addition to the high efficiency and excellent control of regioisomeric impurities, the process is operationally simple by isolating each product via direct crystallization from the reaction mixture with no liquid–liquid extractions or distillation steps needed. We demonstrated the route on >50 kg scale and 46% overall yield to provide the target product in 97% purity by HPLC, which can serve as a useful building block for the preparation of a series of 3,4,5-substituted-7-azaindole derivatives.