Boron tribromide → 1-(2,2-dimethylpropyl)-4-fluoro-5-hydroxy-3-methyl-1,3-dihydro-2H-benzimidazol-2-one

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Reaction Steps

A solution of 1-(2,2-dimethylpropyl)-4-fluoro-5-methoxy-3-methyl-1,3-dihydro-2H-benzimidazol-2-one (7-5, 193 mg, 0.73 mmol) in anhydrous Dichloromethane (10 ml) was cooled to −78 deg C. (Acetone/dry ice) and treated with Boron tribromide (1M in DCM, 1.45 ml, 1.45 mmol, 2 eq). The resulting mixture was allowed to slowly wann to 23 deg C. over 15 h. The reaction was only ˜75% complete by LC/MS, so it was treated with more BBr3 (360 ml, 0.36 mmol, 0.5 eq). The reaction was stirred at 23 deg C. for 1 h, then was carefully quenched by pouring directly into a solution of saturated aqueous NaHCO3 cooled to 0 deg C. The aqueous mixture was extracted with Methylene Chloride (2×200 ml), and the combined organic layers were dried over Na2SO4 and concentrated, thereby providing the title compound, 1-(2,2-dimethylpropyl)-4-fluoro-5-hydroxy-3-methyl-1,3-dihydro-2H-benzimidazol-2-one (7-6), as a green-tan solid. 1H NMR (500 MHz, CDCl3) δ 6.65-6.73 (m, 2H), 3.61 (m, 5H), 1.02 (s, 9H). LRMS m/z: Calc'd for C13H17FN2O2 (M+H) 253.3, found 253.0.

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