General procedure for the synthesis of ethyl 2-oxohexanoate from n-butylzinc bromide and monoethyl oxalyl chloride: a stirred solution of copper iodide (2.29 g, 12 mmol) in anhydrous tetrahydrofuran was cooled to -25 °C and a tetrahydrofuran solution of 0.5 M n-butylzinc bromide (24 mL, 12 mmol) was added slowly dropwise. After addition, the reaction mixture was warmed to 0 °C and stirred at that temperature for 20 min, then cooled to -25 °C again. The reaction mixture was treated dropwise with monoethyl oxalyl chloride (1.37 g, 10 mmol). After stirring at -25 °C for 3 h, the reaction mixture was warmed to room temperature, the reaction was quenched with saturated aqueous ammonium chloride solution and the aqueous layer was extracted with ether. The combined organic phases were washed with brine, filtered, dried over anhydrous sodium sulfate and concentrated in vacuum. The crude product was purified by ISCO fast column chromatography using a pre-populated RediSep silica gel column (gradient elution, 0→20% ethyl acetate in hexane solution) to afford ethyl 2-oxohexanoate (0.60 g, 37%) as a colorless oil.1H NMR (400 MHz, CDCl3) δ 0.91-0.98 (3H, m), 1.34- 1.47 (5H, m), 1.58-1.76 (2H, m), 2.83 (1H, t, J = 7.3 Hz), 4.27-4.37 (2H, m).
