[Br:1][C:2]1[CH:3]=C([CH:7]=[C:8]([Br:10])[CH:9]=1)C=O.CO.C1(C)C=CC(S(O)(=O)=O)=CC=1.[CH3:24][O:25][C:26]([O:29][CH3:30])(C)[CH3:27]>>[Br:1][C:2]1[CH:3]=[C:27]([CH:26]([O:29][CH3:30])[O:25][CH3:24])[CH:7]=[C:8]([Br:10])[CH:9]=1A mixture of 13.2 g (50 mmoles) of crude 3,5-dibromobenzaldehyde, 2 mL (50 mmoles) of methanol, and 100 mg of p-toluenesulfonic acid in 100 mL of 2,2-dimethoxypropane was heated to reflux 6 hrs. After cooling, solvent was removed in vacuo to give a brown oil. This was applied on silica gel and washed with 1:20 ethylacetate:hexane mixture. The filtrate was concentrated to orange brown oil of the desired acetal.
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