[F:1][C:2]1[C:3]([F:21])=[C:4]2[O:8][C:7]([CH3:9])=[CH:6][C:5]2=[C:10]([CH:19]=[O:20])[C:11]=1[O:12]COCCOC.Cl>C1COCC1.CC(OC)(C)C>[F:1][C:2]1[C:3]([F:21])=[C:4]2[O:8][C:7]([CH3:9])=[CH:6][C:5]2=[C:10]([CH:19]=[O:20])[C:11]=1[OH:12]18.0 g (60.0 mmol) of 6,7-difluoro-5-(2-methoxyethoxymethoxy)-2-methylbenzofuran-4-carbaldehyde are stirred for 17 h at 20° C. together with 11.0 ml of conc. HCl in 100 ml of THF. The reaction soln. is diluted with MTBE and washed with water. The aqueous phase is extracted with MTBE, and the combined organic phases are washed successively with water and sat. sodium chloride soln. The solution is dried using sodium sulfate and concentrated to dryness. The crude product is purified by column chromatography (SiO2, 1-chlorobutane), giving 6,7-difluoro-5-hydroxy-2-methylbenzofuran-4-carbaldehyde as a yellow crystalline solid.
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