Imidazole → 2-bromo-(R)-1-tert-butyldimethylsiloxy-1-(3-formamido-4-benzyloxyphenyl)ethane

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(R)-2-Bromo-1-(3-formamido-4-benzyloxyphenyl)ethanol (intermediate 3) (9.9 g, 28 mmol) was dissolved in 36 mL dimethylformamide. Imidazole (2.3 g, 34 mmol) and t-butyldimethylsilylchloride (4.7 g, 31 mmol) were added. The solution was stirred under nitrogen atmosphere for 72 h. Additional imidazole (0.39 g, 5.7 mmol) and t-butyldimethylsilylchloride (0.64 g, 4.3 mmol) were added and the reaction was stirred for an additional 20 h. The reaction was diluted with a mixture of isopropyl acetate (53 mL) and hexanes (27 mL) and transferred to a separatory funnel. The organic layer was twice washed with a mixture of water (27 mL) and saturated aqueous sodium chloride (27 mL) followed by a final wash with saturated aqueous sodium chloride (27 mL). The organic layer was dried over sodium sulfate. Silica gel (23.6 g) and hexanes (27 mL) were added and the suspension was stirred for 10 minutes. The solids were removed by filtration and the filtrate concentrated under vacuum. The residue was crystallized from hexanes (45 mL) to afford 8.85 g (19 mmol, 68%) of intermediate 4 as a white solid. m/z: [M+H+] calcd for C22H30NO3SiBr 464.1, 466.1; found 464.2, 466.4.

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