[CH3:1][N:2]1[CH:6]=[C:5]([NH:7][C:8]([O:10][CH2:11][CH:12]=[CH2:13])=[O:9])[C:4]([O:14][CH3:15])=[C:3]1[C:16]([O:18]CC)=[O:17].[OH-].[Na+].C(O)C>O>[CH3:1][N:2]1[CH:6]=[C:5]([NH:7][C:8]([O:10][CH2:11][CH:12]=[CH2:13])=[O:9])[C:4]([O:14][CH3:15])=[C:3]1[C:16]([OH:18])=[O:17]A mixture of 0.93 g (3.3 mmol) of ethyl 1-methyl-4-[(allyloxycarbonyl)amino]-3-methoxy-1H-pyrrole-2-carboxylate (prepared according to the method described in K. Narkunan, M. A. Ciufolini, Synthesis, 2000, 673-676), 3.3 ml of a 2 molar sodium hydroxide aqueous solution and 3.3 ml of ethanol is stirred at room temperature for 5 days. Water is added and the ethanol is evaporated. After extraction with diethyl ether, the aqueous phase is acidified to pH 2 with concentrated hydrochloric acid. Extraction with ethyl acetate, drying and concentration give 0.6 g (71% yield) of a light brown solid. (M−1=253).
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