Ethyl 2-oxo-2,3-dihydro-1H-benzo[D]imidazole-5-carboxylate (0.073 mol) was used as starting material and dissolved in POCl3 (150 mL) with stirring at 100 °C. Concentrated HCl (about 1.5 mL) was added slowly and cautiously dropwise until the feedstock was completely dissolved. Subsequently, the reaction mixture was warmed up to 120 °C with continuous stirring for 6 hours. Upon completion of the reaction, the solvent was removed by evaporation to dryness. The residue was dissolved in ice water, alkalized with powdered K2CO3 and subsequently extracted with ethyl acetate (containing 10% methanol). The organic layer was separated, dried over MgSO4, filtered and the solvent was evaporated to dryness to give the intermediate ethyl 2-chloro-1H-benzo[d]imidazole-6-carboxylate (13.5 g, 83% yield, melting point: 178 °C).
![ethyl 2-oxo-2,3-dihydro-1H-benzo[d]iMidazole-5-carboxylate](/CAS/GIF/634602-84-9.gif)