A 25 mL THF solution of triethyl phosphonoacetate (44.8 g) was added dropwise to a suspension of THF (150 mL) containing NaH (8.0 g, 60% oil dispersion) over 40 min at 0-10 °C. The reaction mixture was kept at 0-10°C with continued stirring for 0.5 hr. Subsequently, a 25 mL THF solution of cyclobutanone (14.0 g) was added dropwise at the same temperature. The reaction mixture was stirred at 0-10 °C for 2 hours. Next, 50 mL of water was slowly added at 20-30 °C. After removing the organic solvent by distillation under reduced pressure, 150 mL of water was added. The aqueous solution was extracted using MTBE (3 x 100mL). The organic phases were combined and washed with 100 mL of water and subsequently dried with anhydrous MgSO4. After filtration, the solvent was evaporated to give the crude product, which was purified by fractional distillation (81-82 °C/19 mbar) to give 22.2 g (79% yield) of ethyl 2-cyclobutylideneacetate as a colorless liquid. The product was characterized by the following data: 1HNMR (500 MHz, CDCl3) δ 5.58 (m, 1H), 4.13 (q, 2H, J = 7.1 Hz), 3.15-3.12 (m, 2H), 2.85-2.82 (m, 2H), 2.12-2.06 (m, 2H), 1.26 (t, 3H, J = 7.1 Hz); 13C NMR (125 MHz, CDCl3) δ 167.60,166.60,112.38,59.53,33.75,32.32,17.66,14.36; MS (m/z) 140.1; ESI-HRMS m/z calculated for C8H12O2 [M+H]+ 141.0910, found 141.0911.
