[CH2:1]([O:8][C:9]1[CH:10]=[CH:11][C:12]([O:17][CH3:18])=[C:13]([CH:16]=1)[CH:14]=[O:15])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[OH-].[K+].OO.[OH:23]S(O)(=O)=O>CO.O>[CH2:1]([O:8][C:9]1[CH:10]=[CH:11][C:12]([O:17][CH3:18])=[C:13]([CH:16]=1)[C:14]([OH:23])=[O:15])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1
To a stirred suspension of 5-(benzyloxy)-2-methoxybenzaldehyde (7, 1.12 g. 4.6 mmol) in MeOH (8 mL) at room temperature was added a solution of KOH (1.04 g, 18.5 mmol) in water (1.4 mL). The mixture was heated to 65° C. and H2O2 (35 wt %; 4.0 mL, 46 mmol) was added dropwise over 105 min. The reaction mixture was stirred at 65° C. for 1 h. Then it was cooled to room temperature and acidified to pH 2 with 6N H2SO4. The precipitate was collected, washed with water and dried in vacuo to afford the title compound (1.16 g, 97%) as a white solid: 1H NMR (500 MHz, CDCl3) δ 10.94 (br s, 1H), 7.80 (d, J=3.3 Hz, 1H), 7.44-7.37 (m, 4H), 7.35-7.32 (m, 1H), 7.19 (dd, J=9.0, 3.3 Hz, 1H), 7.00 (d, J=9.0 Hz, 1H), 5.08 (s, 2H), 4.04 (s, 3H); ESI MS m/z 257 [M−H]−.
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