NaOtBu (96.1 g, 1.0 mol) was dissolved in THF (1 L) and the solution was cooled to 0°C. A mixture of ethyl chloroacetate (107 mL, 1.0 mol) and diethyl oxalate (136 mL, 1.0 mol) was added slowly and dropwise at this temperature under vigorous mechanical stirring. After the reaction mixture was stirred overnight at room temperature, an aqueous HCl solution (90 mL of concentrated hydrochloric acid mixed with 400 mL of water) was added. The resulting solution was extracted with CH2Cl2 (3 x 200 mL). The organic layers were combined, dried with anhydrous Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by reduced pressure distillation (boiling point range 110-140°C, pressure 10 torr). The product diethyl 2-chloro-3-oxosuccinate was obtained 157.6 g in 71% yield.1H NMR (CDCl3, 400 MHz) δ= 1.31 (t, J = 7.2Hz, 3H), 1.39 (t, J = 7.2Hz, 3H), 4.31 (q, J = 7.2Hz, 2H), 4.39 (q, J = 7.2Hz, 2H), 4.39 (q, J = 7.2Hz, 2H) 5.46 (s, 1H).
