Step 2: Formic acid (1 mL) was added to a mixed solution of 4-bromo-5-methoxybenzene-1,2-diamine (3.8 g, 18 mmol) and triethyl orthoformate (50 mL) prepared in Step 1 under stirring conditions. The reaction mixture was heated to reflux for 3 hours and subsequently concentrated under reduced pressure. The concentrated residue was extracted by partitioning with ethyl acetate (200 mL) and 1N aqueous sodium carbonate solution (100 mL). The organic layer (ethyl acetate layer) was separated, washed with brine (100 mL), dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give 5-bromo-6-methoxy-1H-benzo[d]imidazole (4.0 g) as a brown oil. The product was used directly in the subsequent reaction without further purification.LCMS (ESI) m/z 228 and 230 (M + H)+.
