a) Synthesis of diethyl 2-(1-ethoxyethylidene) malonate. A mixture of diethyl acetylmalonate (10 g, 0.049 mol), triethyl orthoacetate (24 g, 0.15 mol) and zinc chloride (70 mg, 0.0049 mol) was stirred and reacted at 95 °C for 4 h under inert atmosphere. After completion of the reaction, the reaction mixture was concentrated and the residue was purified by silica gel column chromatography (eluent: ethyl acetate/petroleum ether=10:90) to afford the target product diethyl 2-(1-ethoxyethylidene)malonate as an oil (6.4 g, 56% yield). The product was analyzed by LC/MS: MS (ES+) m/e 231 (MH+); 1H NMR (300 MHz, CDCl3) δppm 1.22-1.33 (m, 9H), 2.43 (s, 3H), 4.06 (q, J=6.9 Hz, 2H), 4.16 (q, J=7.2 Hz, 2H), 4.26 (q, J=7.2 Hz, 2H).
