General procedure for the synthesis of ethyl 3-aminocrotonate from ethyl acetoacetate: β-keto ester (1.0 eq.), ammonium acetate (3.0 eq.), and acetic acid (dropwise) were dissolved in dry toluene (6 mL) in a 10 mL reaction glass vial containing a stirring magnet and a molecular sieve. The vial was tightly sealed with an Aluminum-Teflon convoluted cap and the mixture was microwaved at 140 °C for 20 min at 60 W power. After completion of the reaction, it was cooled to 50 °C by gas injection. The crude reaction mixture was partitioned between ethyl acetate (15 mL) and saturated sodium bicarbonate solution (15 mL), and the aqueous layer was extracted with ethyl acetate (3 x 15 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by rapid chromatography on silica gel.Synthesis of ethyl 3-aminobut-2-enoate (6a): ethyl 3-(2-fluorophenyl)-3-oxopropanoate 5a (1.0 eq.), ammonium acetate (4.0 eq.), and acetic acid (7 drops) were reacted under the above conditions. Rapid chromatographic purification using hexane/ethyl acetate (80:20 to 70:30) as eluent gave an analytically pure product in 89% yield.1H NMR (CDCl3, 300 MHz) δ (ppm): 1.24 (t, 3H, J=7.36 Hz), 3.51 (s, 3H), 4.09 (q, 2H, J=7.28 Hz). 4.60 (s, 1H).
