In the same manner as in Starting Material Synthesis Example 4 and using ethyl 2-aminobenzo[b]thiophene-3-carboxylate (6.0 g), 2,5-dibromonitrobenzene (8.5 g) and dimethyl sulfoxide (70 ml), crude crystals (7.3 g) of ethyl 2-(4-bromo-2-nitroanilino)benzo[b]thiophene-3-carboxylate were obtained. Without purification, in the same manner as in Starting Material Synthesis Example 21 and using ethanol (70 ml), 18% hydrochloric acid (70 ml) and tin(II) chloride.dihydrate (15.7 g), ethyl 2-(2-amino-4-bromoanilino)benzo[b]thiophene-3-carboxylate (3.3 g) was obtained.
