OS(O)(=O)=O.[C:6]1([CH:12]([CH2:17][C:18]([OH:20])=[O:19])[CH2:13][C:14]([OH:16])=[O:15])[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=1.[N+:21]([O-])([OH:23])=[O:22]>>[N+:21]([C:9]1[CH:8]=[CH:7][C:6]([CH:12]([CH2:17][C:18]([OH:20])=[O:19])[CH2:13][C:14]([OH:16])=[O:15])=[CH:11][CH:10]=1)([O-:23])=[O:22]A flask charged with concentrated H2SO4 (400 mL) was cooled to 0° C. and treated with 50.0 g (240 mmol) of 3-phenyl-pentanedioic acid portionwise over 20 min and with fuming HNO3 (10 mL) dropwise over 20 min. The mixture was stirred at RT for 3 h, poured over ice (amount equivalent to 1000 mL), and the precipitate was filtered, washed with cold water, air-dried, and dried in a vacuum dessicator. The solid was triturated with a minimum amount of CH3CN, filtered, and air-dried. The filtrate was concentrated and triturated again with a minimum amount of CH3CN, filtered, and air-dried to afford a second batch. The two batches were combined to afford 56.9 g (94%) of the title compound as an off-white solid: 1H-NMR (DMSO-d6; 400 MHz): δ 8.15 (d, 2H, J=8.8 Hz), 7.58 (d, 2H, J=8.8 Hz), 3.62-3.50 (m, 1H), 2.79-2.57 (m, 4H).
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