In t-butanol (500 ml) were dissolved ethyl 4-(4-bromo-2,N-diformylanilino)butyrate (15.32 g) and potassium t-butoxide (5.53 g), and the mixture was refluxed for 30 minutes. To the mixture were added water (500 ml) and 1N hydrochloric acid (50 ml), and the mixture was extracted with ethyl acetate (1000 ml). The organic layer was washed with saturated brine (200 ml) and dried with magnesium sulfate. The solvent was evaporated under reduced pressure, and the residue was purified with silica gel column chromatography (300 g, hexane:ethyl acetate=4:1→1:1) to give ethyl 7-bromo-1-formyl-2,3-dihydro-1-benzazepine-4-carboxylate (3.13 g, 22%) and 7-bromo-1-formyl-2,3-dihydro-1-benzazepine-4-carboxylic acid (1.39 g, 10%).
