Methyl 3,4-diaminobenzoate (5.00 g, 30.1 mmol) was dissolved in THF (40 mL) at 0 °C, followed by the addition of N,N'-carbonyldiimidazole (7.32 g, 45.1 mmol). The reaction mixture was stirred at 0 °C for 16 h and gradually warmed up to 23 °C. Upon completion of the reaction, 1M HCl aqueous solution (50 mL) was slowly added followed by water (70 mL) at 0 °C and stirring was continued for 1 hour. The resulting precipitate was collected by filtration and dried under reduced pressure for 18 h to afford methyl 2-oxo-2,3-dihydro-1H-benzo[d]imidazole-5-carboxylate (5.45 g, 94% yield), and the product could be used for subsequent reactions without further purification. Mass spectrum (ESI/CI): calculated value C9H8N2O3, 192.1; measured value m/z 193.1 [M+H]+. 1H NMR (400 MHz, CDCl3) δ: 11.01 (s, 1H), 10.84 (s, 1H), 7.63 (dd, J=8.2,1.6Hz, 1H), 7.47 (s, 1H). 7.02 (d, J=8.2Hz, 1H), 3.82 (s, 3H).
