[CH2:1]([O:8][C:9]([NH:11][C:12]([CH2:23][CH2:24][CH:25]=[CH2:26])([C:18]([O:20]CC)=[O:19])[C:13]([O:15][CH2:16][CH3:17])=[O:14])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[OH-].[K+].CC(O)=O>C(O)C>[CH2:1]([O:8][C:9]([NH:11][C:12]([C:13]([O:15][CH2:16][CH3:17])=[O:14])([CH2:23][CH2:24][CH:25]=[CH2:26])[C:18]([OH:20])=[O:19])=[O:10])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A solution of diethyl 2-(benzyloxycarbonylamino)-2-(but-3-enyl)malonate (4.8 g, 13.23 mmol) in ethanol (45 mL) was cooled to −30° C. and treated with an aqueous solution of potassium hydroxide (1.55 g, 27.76 mmol in 15 mL water). After the addition was complete, the solution was warmed to 0° C. for 30 minutes followed by room temperature for 1 h. With the reaction complete, the mixture was acidified with AcOH (1.8 g) and extracted with ethyl acetate (1×50 mL). The aqueous layer was acidified to pH 3 with 3 N hydrochloric acid and extracted with ethyl acetate (2×50 mL). The combined organic layers were washed with saturated aqueous sodium chloride (1×50 mL), dried over MgSO4 and concentrated to give 2-(benzyloxycarbonylamino)-2-(ethoxycarbonyl)hex-5-enoic acid (3.0 g, 68%). 1H NMR (CDCl3) δ 10.00 (bs, 1H), 7.37 (m, 5H), 7.26-6.93 (m, 1H), 6.21 (bs, 1H), 5.76 (m, 1H), 5.94-5.22 (m, 4H), 4.27 (m, 2H) 2.43 (m, 2H), 1.96-1.93 (m, 2H), 1.27-1.21 (m, 3H). MS found for C17H21NO6 m/z [336 (M+1)].
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