Step A: Synthesis of ethyl 3-bromo-2-oxobutanoate (1-B). Bromine (1.89 mL, 36.9 mmol) was added slowly and dropwise to a solution of ethyl 2-oxobutyrate (1-A, 4.8 g, 36.9 mmol) in dichloromethane (20 mL) at 5 °C. The reaction mixture was gradually warmed to room temperature and stirred continuously for 18 hours. Upon completion of the reaction, the reaction mixture was purged with nitrogen to remove residual bromine. Subsequently, the reaction mixture was diluted with ethyl acetate and the organic phase was washed sequentially with 10% sodium bicarbonate solution (2 times), water and saturated saline. The organic layer was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give ethyl 3-bromo-2-oxobutanoate as a yellow oil (1-B, 7.50 g, 97% yield).1H-NMR (CDCl3) data: δ 5.15-5.20 (q, 1H), 4.32-4.45 (m, 2H), 1.82-1.85 (d, 3H), 1.38- 1.41 (t, 3H).
