4-Azidophenacyl bromide → 2-Amino-5-(4-azidophenyl)imidazole-1-carboxylic acid tert-butyl ester

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To a solution of 1-(4-azidophenyl)-2-bromoethanone (1.50 g, 6.24 mmol) in anhydrous DMF (20 mL) was added Boc-guanidine (3.00 g, 18.7 mmol). The reaction was stirred at ambient temperature for 48 hours upon which the mixture was partitioned between EtOAc (150 mL) and water (75 mL). The organic layer was successively washed with water (3×50 mL) and brine (2×50 mL) before being dried (Na2SO4) and evaporated to dryness. The resulting crude oil was purified via flash column chromatography (10-50% EtOAc/Hexanes) to obtain the target 2-amino-5-(4-azidophenyl)imidazole-1-carboxylic acid tert-butyl ester (1.84 g, 58%) as a yellow solid: 1H NMR (300 MHz, DMSO-d6) δ 7.77 (d, 2H, J=8.1 Hz), 7.36 (s, 1H), 7.10 (dd, 2H, J=0.9, 8.1 Hz), 6.61 (br s, 2H), 1.58 (s, 9H); 13C NMR (75 MHz, DMSO-d6) δ 150.4, 148.9, 137.6, 136.2, 130.5, 126.2, 119.1, 106.2, 84.7, 27.5; HRMS (ESI) calcd for C8H6BrN3O (M+) 300.1335. found 300.1329.

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