General procedure for the synthesis of ethyl ethoxy-2-methylene trifluoroacetoacetate from triethyl orthoformate and ethyl trifluoroacetoacetate: ethyl 4,4,4-trifluoro-3-oxobutanoate (30 g, 162.9 mmol) was added to a solution of acetic anhydride (50 mL) containing triethoxymethane (72.4 g, 488.8 mmol). The reaction mixture was stirred continuously at 135 °C for 18 hours. Upon completion of the reaction, the brown mixture was concentrated to afford ethyl 2-(ethoxymethylene)-4,4,4-trifluoro-3-oxobutanoate (38 g, 97.1% yield), the product was a brown oil that could be used in subsequent reactions without further purification. The product was characterized by 1H NMR (400 MHz, CDCl3): δ 1.23-1.33 (m, 3H), 1.40 (dt, J = 14.18, 7.19 Hz, 3H), 4.19-4.36 (m, 4H), 7.66-7.87 (m, 1H).
