To a 200 mL round bottom flask equipped with a magnetic stirrer was added mono-tert-butyl malonate (3.0 g, 18.7 mmol) and methanol (70 mL). To this solution was added hafnium(IV) chloride tetrahydrofuran complex (1:2) (88 mg, 0.19 mmol). The reaction mixture was stirred at room temperature for 48 hours. After completion of the reaction, saturated saline was added to the mixture and extracted with dichloromethane (3 x 70 mL). The organic layers were combined, dried with anhydrous magnesium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: n-hexane/ethyl acetate = 50:50) to afford the target compound tert-butyl methyl malonate (3.0 g, 91% yield) as a colorless oily liquid.1H NMR (400 MHz, CDCl3) δ 3.74 (s, 3H), 3.30 (s, 2H), 1.47 (s, 9H); 13C NMR ( 100 MHz, CDCl3) δ 167.5, 165.8, 82.1, 52.3, 42.7, 27.9; HR-FAB MS m/z calculated value C8H15O4 [M+H]+ 175.0883, measured value 175.0875.
