FC(F)(F)C(O)=O.[BH4-].[Na+].[Cl:10][C:11]1[CH:16]=[C:15]([Cl:17])[CH:14]=[CH:13][C:12]=1[CH:18](O)[C:19]1[C:20]2[CH:28]=[C:27]([C:29]([O:31][CH3:32])=[O:30])[CH:26]=[CH:25][C:21]=2[O:22][C:23]=1[CH3:24].[OH-].[Na+]>C(Cl)Cl>[Cl:10][C:11]1[CH:16]=[C:15]([Cl:17])[CH:14]=[CH:13][C:12]=1[CH2:18][C:19]1[C:20]2[CH:28]=[C:27]([C:29]([O:31][CH3:32])=[O:30])[CH:26]=[CH:25][C:21]=2[O:22][C:23]=1[CH3:24]Trifluoroacetic acid (50 ml) was ice-cooled and sodium borohydride (873 mg, 23.1 mmol) was gradually added over 20 min under a nitrogen atmosphere at 5-7° C. Thereto was dropwise added a solution of 3-((2,4-dichlorophenyl)hydroxymethyl)-5-(methoxycarbonyl)-2-methylbenzo[b]furan in methylene chloride over 20 min, and the mixture was stirred at room temperature for 45 min. After the completion of the reaction, the reaction mixture was poured into ice water and a 25% aqueous sodium hydroxide solution was added to make an alkali solution. The solution was extracted with ethyl acetate. The organic layer was washed with saturated brine, and dried over anhydrous magnesium sulfate. The desiccant was filtered off and the filtrate was concentrated under reduced pressure. The crystalline residue was purified by silica gel column chromatography to give the objective compound (0.58 g, 72% in 2 steps) as colorless crystals.
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