[O:1]1[CH2:5][CH2:4][C:3]2[CH:6]=[CH:7][CH:8]=[C:9]([C:10]([OH:12])=[O:11])[C:2]1=2.[Br:13]Br.O>C(O)(=O)C.[Fe]>[Br:13][C:7]1[CH:8]=[C:9]([C:10]([OH:12])=[O:11])[C:2]2[O:1][CH2:5][CH2:4][C:3]=2[CH:6]=1To an ice-cooled acetic acid solution (5 ml) of 2,3-dihydrobenzo[b]furan-7-carboxylic acid (15a) (0.33 g, 2.0 mmol) there was added iron (8 mg, 0.14 mmol) and bromine (0.32 g, 2.0 mmol) in 1 ml of acetic acid. The mixture was stirred at room temperature for 18 hours and then poured into water (20 ml). After cooling in the freezer for 11/2 hours the product was collected on a filter, and recrystallized from ethyl acetate to give 0.24 g (50.3%) of 15b as a white crystalline solid, mp 228°-229° C.
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