[CH2:1]([C:3]1[CH:17]=[CH:16][C:6]2[O:7][CH:8]([C:11]([O:13][CH2:14][CH3:15])=[O:12])[CH2:9][O:10][C:5]=2[CH:4]=1)[CH3:2].C([O:22]O)(C)(C)C>C(Cl)Cl.[O-2].[O-2].[O-2].[Cr+6]>[C:1]([C:3]1[CH:17]=[CH:16][C:6]2[O:7][CH:8]([C:11]([O:13][CH2:14][CH3:15])=[O:12])[CH2:9][O:10][C:5]=2[CH:4]=1)(=[O:22])[CH3:2]Add 2 g (8.5 mmol) of ethyl 6-ethyl-2,3-dihydro-1,4-benzodioxin-2-carboxylate dissolved in 5 cm3 of anhydrous methylene chloride to a mixture at 0° C. of 0.042 g (0.42 mmol) of chromium trioxide and 5.35 g (59.3 mmol) of 70% tert-butyl hydroperoxide in 30 cm3 of methylene chloride. Stir for 2 hours at 0° C. and then for 72 hours at room temperature. The crude product obtained by concentrating to dryness is purified by chromatography on a silica column (eluant: methylene chloride). Ethyl 6-acetyl-2,3-dihydro-1,4-benzodioxin-2-carboxylate is thereby obtained in a yield of 62%.
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