To a solution of 4-(5-amino-3-tert-butyl-pyrazol-1-yl)-benzoic acid methyl ester (5.3 g, 19.4 mmol) in anhydrous THF (200 mL) was slowly added phenyl chloroformate (6.81 mL, 54.3 mmol), followed by sodium carbonate (2.1 g, 19.4 mmol). The mixture was stirred at room temperature overnight. Ethyl acetate (500 mL) was added, followed by saturated sodium carbonate (300 mL). The organic layer was washed with saturated sodium carbonate (3×) and brine (1×), dried over MgSO4, and concentrated at reduced pressure. The residue was washed with ether to give 4.3 g (56%) of the desired product. 1H-NMR (DMSO-d6) δ 10.19 (s, 1H), 8.10 (d, J=9.0 Hz, 2H), 7.73 (d, J=9.0 Hz, 2H), 7.38-7.11 (m, 5H), 6.41 (s, 1H), 3.87 (s, 3H), 1.27 (s, 1H); MS LC-MS [M+H]+=394.1, RT=3.53 min.
