[C:1]([NH:4][C:5]([CH2:16]/[CH:17]=[CH:18]/[CH3:19])([C:11]([O:13]CC)=[O:12])[C:6]([O:8]CC)=[O:7])(=[O:3])[CH3:2].[OH-].[Na+]>C(O)C.O>[C:1]([NH:4][C:5]([CH2:16]/[CH:17]=[CH:18]/[CH3:19])([C:11]([OH:13])=[O:12])[C:6]([OH:8])=[O:7])(=[O:3])[CH3:2]39.63g (146 mmol) of diethyl (E)-2-acetamido-2-(2-butenyl)malonate were dissolved in 200 ml of ethanol and a solution of 19.24 g (481 mmol) of sodium hydroxide in 100 ml of water was added. The mixture was stirred for 2 hours at 60° C., evaporated to dryness under a vacuum and the residue was partitioned between diethyl ether and water. The aqueous phase was acidified with 2M hydrochloric acid and extracted with ethyl acetate. The organic phase was dried over magnesium sulphate and the solvent was removed by evaporation under a vacuum to give 26.1 g of (E)-2-acetamido-2-(2-butenyl)malonic acid as a white solid which was used in the next step without further purification. 1H NMR (250 MHz, MeOD) δ: 1.65 (d, 3H), 2.0 (s, 3H), 2.9 (d, 2H), 5.25 (m, 1H), 5.5 (m, 1H).
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