[C:1]1([C:3](=[CH:5][CH:6]=[CH:7][CH:8]=1)[OH:4])[OH:2].Br[C:10](Br)([C:16]([O:18][CH2:19][CH3:20])=[O:17])[C:11]([O:13][CH2:14][CH3:15])=[O:12].C(=O)([O-])[O-].[K+].[K+]>CC(C)=O>[CH2:19]([O:18][C:16]([C:10]1([C:11]([O:13][CH2:14][CH3:15])=[O:12])[O:4][C:3]2[CH:5]=[CH:6][CH:7]=[CH:8][C:1]=2[O:2]1)=[O:17])[CH3:20]Ex-1A: Catechol (2.2 g, 20 mmol) was dissolved in acetone. Diethyl dibromomalonate (7.0 g, 22 mmol) and potassium carbonate (2.76 g) were added, and the mixture was stirred at room temperature overnight. The solvent was removed under reduced pressure, and water was added to the residue. The residue was extracted with dichloromethane, and the organic phase was washed with brine, dried over magnesium sulfate and evaporated. Chromatography (hexanes/ethyl acetate, 4:1) gave 3.9 g of benzo[1,3]dioxole-2,2-dicarboxylic acid diethyl ester. 1H-NMR (CDCl3) δ 6.90–6.97 (m, 4H), 4.37 (q, J=7 Hz, 4H), 1.32 (t, J=7 Hz, 6H).
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