[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][N:11]([CH2:14][C:15]([O:17]C)=[O:16])[C:10](=[O:19])[CH:9]1[CH2:20][C:21]1[CH:26]=[CH:25][C:24]([O:27][CH2:28][C:29]2[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=2)=[CH:23][CH:22]=1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[Li+].[OH-]>CO>[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][N:11]([CH2:14][C:15]([OH:17])=[O:16])[C:10](=[O:19])[CH:9]1[CH2:20][C:21]1[CH:22]=[CH:23][C:24]([O:27][CH2:28][C:29]2[CH:30]=[CH:31][CH:32]=[CH:33][CH:34]=2)=[CH:25][CH:26]=1)=[O:7])([CH3:4])([CH3:2])[CH3:3]t-Boc-piperazinoneacetate 4a (0.251 g, 5.37 ×10-4 mole), 1M aqueous LiOH (0.59 ml, 5.9 ×10-4 mole), and methanol (2 ml) are stirred at room temperature for 2 hours. The solvent is then evaporated and the resulting yellow oil is dissolved in CH2Cl2 and transferred to a separatory funnel where it is washed with 0.5M aqueous HCl. The CH2Cl2 layer is separated and the acidic aqueous phase is extracted with CH2Cl2 (3 times). The CH2Cl2 extracts are combined and washed with saturated aqueous NaCl before being dried over Na2SO4. Filtration of the drying agent and evaporation of the filtrate gives 5a as a colorless form, which was shown to be homogeneous by TLC on silica gel plates. The structure of 5a was corroborated by NMR. NMR (CDCl3) δ1.27 (S, 9, t-boc), 3.09-4.07 (m, 8, methylenes), 4.68 (t, 1, C3 --H), 4.97 (S, 2, benzyloxy methylene), 6.89 (q, 4, aromatic), 7.30 (S, 5, aromatic), 9.99 (broad S, 1, acid).
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