[N:1]1([C:23]([O:25][C:26]([CH3:29])([CH3:28])[CH3:27])=[O:24])[CH2:6][CH2:5][C:4]2([O:11][C:10]3[CH:12]=[C:13]([C:16]([O:18]C)=[O:17])[CH:14]=[CH:15][C:9]=3[N:8]3[CH:20]=[CH:21][CH:22]=[C:7]23)[CH2:3][CH2:2]1.[Li+].[OH-]>O1CCOCC1.C(OCC)(=O)C>[C:26]([O:25][C:23]([N:1]1[CH2:2][CH2:3][C:4]2([O:11][C:10]3[CH:12]=[C:13]([C:16]([OH:18])=[O:17])[CH:14]=[CH:15][C:9]=3[N:8]3[CH:20]=[CH:21][CH:22]=[C:7]23)[CH2:5][CH2:6]1)=[O:24])([CH3:29])([CH3:27])[CH3:28]A solution of 1′-tert-butyl 7-methyl spiro[benzo[b]pyrrolo[1,2-d][1,4]oxazine-4,4′-piperidine]-1′,7-dicarboxylate (3.5 g, 8.8 mmol) in LiOH (18 mL of 2.0 M, 35.1 mmol) and dioxane (18 mL) was stirred at 55° C. for 1 hour. The reaction mixture was diluted with ethyl acetate and was washed with water. The aqueous layer was acidified with 1N HCl and the product was extracted into ethyl acetate. The organics were dried over sodium sulfate, filtered and evaporated to yield 1′-(tert-butoxycarbonyl)spiro[benzo[b]pyrrolo[1,2-d][1,4]oxazine-4,4′-piperidine]-7-carboxylic acid which was used without further purification. ESI-MS m/z calc. 384.4. found 385.3 (M+1)+. Retention time: 1.81 minutes (3 min run).
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