[CH3:1][C:2]1([CH3:13])[C:6]2[C:7]([O:11]C)=[CH:8][CH:9]=[CH:10][C:5]=2[O:4][CH2:3]1.B(Br)(Br)Br.O>ClCCl>[CH3:1][C:2]1([CH3:13])[C:6]2=[C:7]([OH:11])[CH:8]=[CH:9][CH:10]=[C:5]2[O:4][CH2:3]1To a solution of 3,3-dimethyl-4-(methyloxy)-2,3-dihydro-1-benzofuran (Intermediate 5, 4.0 g) in dichloromethane (100 ml, SCRC) was added BBr3 (6.37 ml, 67.3 mmol, SCRC) dropwise under ice-cooling. After the addition was complete, the reaction mixture was stirred for 2 hours at room temperature and then water (20 ml) was added. The resulting mixture was extracted with ethyl acetate (3 times 100 ml, SCRC) and the combined organic layers were dried, evaporated and purified by silica gel chromatography with EtOAc/PE as eluents (1/20) to afford the title compound (2.8 g).
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