[C:1]([C:4](=[C:10](OCC)[CH3:11])[C:5]([O:7][CH2:8][CH3:9])=[O:6])(=O)[CH3:2].C(O)(=O)C.[CH:19]([NH2:21])=[NH:20].[O-]CC.[Na+]>C(O)C>[CH3:2][C:1]1[C:4]([C:5]([O:7][CH2:8][CH3:9])=[O:6])=[C:10]([CH3:11])[N:21]=[CH:19][N:20]=1Ethyl 2-acetyl-3-ethoxybut-2-enoate (10.7 g, 0.0537 mol), formamidine acetate (5.6 g, 0.054 mol) and sodium ethoxide (2.7 M in ethanol, 20.0 mL) were mixed in ethanol (30 mL) and the mixture was stirred at 90° C. for 4 h. The reaction mixture was cooled, quenched with water and concentrated. The crude material was purified by flash chromatography on silica gel, eluting with 10%, 50% ethyl acetate/hexane to afford the desired product (7.4 g, 76%) as a yellow oil. MS (EI) 181.1 (M+1). 1H NMR (300 MHz, CDCl3) δ (ppm) 8.97 (s, 1H), 4.44 (q, 2H), 2.56 (s, 6H), 1.42 (t, 3H).
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