70201-42-2

625-92-3

107-31-3

70201-42-2

Step 1: Diisopropylamine (2.4 g, 24.0 mmol) was dissolved in anhydrous tetrahydrofuran (20 mL) under nitrogen protection and cooled to 0 °C. A n-butyllithium solution (9.6 mL, 24.0 mmol) in hexane was slowly added dropwise and stirred continuously for 30 min at this temperature. Subsequently, additional anhydrous tetrahydrofuran (30 mL) was added and the reaction mixture was further cooled to -78 °C. To this low-temperature solution, dry 3,5-dibromopyridine (4.7 g, 20 mmol) was added, diluted dropwise with tetrahydrofuran (50 mL), and stirring was continued for 30 minutes. Next, methyl formate (2.4 g, 40 mmol) was added and the reaction mixture was continued stirring at -78 °C for 30 min. After slowly warming to room temperature, the reaction was quenched with saturated sodium bicarbonate solution (100 mL) and extracted with ethyl acetate (50 mL × 3). The organic phases were combined, dried over anhydrous sodium sulfate, concentrated and purified by column chromatography to afford the target product 3,5-dibromopyridine-4-carbaldehyde (26-b) as a light yellow solid (4.0 g, 75% yield).1H NMR (300 MHz, DMSO-d6) δ: 10.06 (s, 1H), 8.87 (s, 2H).