[Br:1][C:2]1[CH:7]=[CH:6][C:5]([CH:8]([OH:12])[C:9]([OH:11])=[O:10])=[CH:4][CH:3]=1.S(=O)(=O)(O)O.C(=O)([O-])[O-].[Na+].[Na+].[CH3:24][C:25]([CH3:27])=O>O>[Br:1][C:2]1[CH:3]=[CH:4][C:5]([CH:8]2[O:12][C:25]([CH3:27])([CH3:24])[O:10][C:9]2=[O:11])=[CH:6][CH:7]=1(4-Bromo-phenyl)-hydroxy-acetic acid (97 g, 0.42 mol) is dissolved in 200 ml of acetone and cooled to −10° C. At this temperature 23 ml of concentrated sulfuric acid are added dropwise. After the addition is complete, the reaction mixture is stirred at −10° C. for further 30 minutes and is subsequently poured into a cooled (0° C.) solution of sodium carbonate (86 g, mol) in 800 ml of water. The crystalline 5-(4-bromo-phenyl)-2,2-dimethyl-[1,3]dioxolan-4-one is filtered, washed with ice-cold water and dried in the high-vacuum. 1H-NMR (300 MHz, CDCl3): 1.72 (s, 3H, CH3), 1.76 (s, 3H, CH3), 5.37 (s, 1H, CHO), 7.37 (d, 2H, CH arom.), 7.56 (d, 2H, CH arom.).
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