General procedure for the synthesis of ethyl 3-formyl-2-butenoate from ethyl (E)-4-hydroxy-3-methylbut-2-enoate: to a vigorously stirred solution of ethyl (E)-4-hydroxy-3-methylbut-2-enoate (9.37 g, 65 mmol) in dichloromethane (1.3 L) was added activated manganese dioxide powder (56.5 g, 650 mmol). The resulting suspension was stirred at room temperature for 1 hour and then filtered through a diatomaceous earth pad. The filtrate was evaporated to give pure ethyl 3-formyl-2-butenoate as a yellow oil. Yield: 7.66 g (92%); Thin Layer Chromatography (Spreading Agent D) Rf Value: 0.35; IR Spectra (pure sample, cm-1 ): 2829, 2740, 1718, 1660; GC-MS (electron bombardment, 20 eV): retention time = 4.82 min, mass-to-charge ratio (relative abundance): 142 (4, [M]+), 114 (15, [M- CO]+), 97 (100, [M-OCH2CH3]+), 96 (100, [M-CH3CH2OH]+); 1H nuclear magnetic resonance (CDCl3, δ): 9.54 (s, 1H), 6.49 (q, 1H, unresolved), 4.26 (q, 2H, J=6.8 Hz), 2.15 (d, 3H, J=1.2 Hz), and 1.33 (t, 3H, J=7.2Hz); 13C NMR (CDCl3, δ): 194.8, 165.7, 150.6, 135.8, 61.3, 14.4, 11.0.
