Boron tribromide → (Rac)-4-bromo-2-[7-oxo-4-(3-trifluoromethyl-phenyl)-[1,4]diazepan-1-yl]-butyric acid methyl ester

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Reaction Steps

A solution of 1.03 g (2.12 mmol) of (rac)-4-(tert-butyl-dimethyl-silanyloxy)-2-[7-oxo-4-(3-trifluoromethyl-phenyl)-[1,4]diazepan-1-yl]-butyric acid methyl ester in 6 ml of CH2Cl2 was treated at 0° C. with 2.33 ml (2.33 mmol, 1M in CH2Cl2) of boron tribromide and kept 2.5 h at this temperature. The solution was warmed to RT cooled (0° C.) and treated again with 2.33 ml (2.33 mmol, 1M in CH2Cl2) of boron tribromide. After 1 h at this temperature, the reaction was extracted with cold sat. aq. NaHCO3 and EtOAc solution (3×). The organic phases were washed with sat. aq. NaHCO3 solution, dried over Na2SO4 and evaporated to give 1.14 g of the crude compound. Purification by flash silica gel column ((n-heptane:EtOAc 95:5, 1:1 to EtOAc) gave 0.086 g (11%) of the title compound as light yellow oil, MS: 437.1 (MH+, 1Br) and

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