1,1'-Carbonyldiimidazole → tert-Butyl 1-(3,5-dibromopyrazin-2-ylamino)-2-methyl-1-oxopropan-2-ylcarbamate

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Reaction Steps

1,1′-Carbonyldiimidazole (2.63 g, 16.24 mmol) was added to a stirred solution of 2-(tert-butoxycarbonylamino)-2-methylpropanoic acid (3.00 g, 14.76 mmol) in N,N-dimethylformamide (4 mL) and dichloromethane (8 mL) at room temperature. The resulting clear colorless mixture was stirred at room temperature under nitrogen for 3 h. N,N-Diisopropylethylamine (3.86 mL, 22.14 mmol) was added followed by 3,5-dibromopyrazin-2-amine (5.60 g, 22.14 mmol). The resulting mixture was heated at 50° C. under a reflux condenser under nitrogen for 71 h. Dichloromethane was removed under reduced pressure. The residue was diluted with ethyl acetate and washed with water. The water layer was extracted with ethyl acetate. The combined organics were washed with brine, dried over magnesium sulfate, filtered and concentrated under reduced pressure. The residue was triturated with 30% ethyl acetate in hexane and solids collected by vacuum filtration. The filtrate was concentrated under reduced pressure and purified using flash chromatography (5-50% ethyl acetate in hexane). Fractions containing the desired product were combined with the solids obtained by filtration and concentrated under reduced pressure. The residue was dried under high vacuum to give the desired product (2.38 g, 5.43 mmol, 37% yield) as an off-white solid. MS (ESI) m/z 439.3 [M+1]+, 461.1 [M+Na]+.

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