General procedure for the synthesis of 3-trifluoromethylphenylhydrazine hydrochloride from m-bromobenzotrifluoride: CuBr (36 mg, 0.25 mmol, 2.5 mol%), ligand L3 (110 mg, 0.4 mmol, 4 mol%), H2O (0.5 mL), and K3PO4 (254 mg, 1.2 mmol) were added and mixed in a 15 mL screw-top capped test tube. STAC (110 mg, 0.3 mmol, 3 mol%) and m-bromobenzotrifluoride (10 mmol) were then added, and the resulting mixture was stirred at 80-110°C (oil bath temperature) for 10 min. Next, K3PO4 (2.29 g, 10.8 mmol) and N2H4-H2O (1 g, 20 mmol) were added and argon gas (flow rate 5-7 mL/min) was bubbled through the reaction mixture for 5 min. The reaction mixture was stirred in a closed test tube at 80-110°C (oil bath temperature) for 1-2 h. The progress of the reaction was monitored by TLC (eluent: hexane) until the feedstock was completely consumed. After completion of the reaction, it was cooled to room temperature and diluted with dichloromethane (50 mL). The resulting solution was filtered and washed with saturated saline (225 mL). A 37% aqueous HCl solution was added dropwise to the dichloromethane solution until the pH reached 3-4. The precipitate formed was filtered, washed with dichloromethane (15 mL) and dried at room temperature. NMR spectra of the partially synthesized 3-trifluoromethylphenylhydrazine hydrochloride showed the presence of 1-5 mol% of the corresponding aniline hydrochloride as an impurity (see Supplementary Data). To obtain an analytically pure sample, it can be purified by precipitation by adding 2-3 volumes of diethyl ether from a methanol solution.
