C([O:3][C:4]([C:6]1[S:7][C:8]2[CH2:9][CH2:10][O:11][C:12]3[CH:19]=[CH:18][C:17]([Br:20])=[CH:16][C:13]=3[C:14]=2[N:15]=1)=[O:5])C.[Li+].[OH-].C1COCC1>O>[Br:20][C:17]1[CH:18]=[CH:19][C:12]2[O:11][CH2:10][CH2:9][C:8]3[S:7][C:6]([C:4]([OH:5])=[O:3])=[N:15][C:14]=3[C:13]=2[CH:16]=1To 9-Bromo-4,5-dihydro-6-oxa-3-thia-1-aza-benzo[e]azulene-2-carboxylic acid ethyl ester (2.52 g, 7.11 mmol) and LiOH (1.53 g, 36.6 mmol) was added THF (6.5 mL) and water (6.5 mL) and allowed to stir at room temperature overnight. The reaction mixture was concentrated under reduced pressure to remove the THF. The reaction mixture was diluted with EtOAc and 1 N HCl and warmed in a water bath to solubilize the solid. The layers were separated and the organic extract was washed sequentially with water and brine. The combined organic extracts were dried over MgSO4 and filtered. The filtrate was concentrated under reduced pressure to give 9-Bromo-4,5-dihydro-6-oxa-3-thia-1-aza-benzo[e]azulene-2-carboxylic acid. LC/MS (ESI+): m/z 327 (M+H)
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