To anhydrous acetic acid (0.65 ml) was added formic acid (0.32 ml) at 0° C., and the mixture was stirred at 60° C. for 2 hours, air-cooled and diluted with THF (10 ml). In THF (10 ml) was dissolved methyl 7-(4 propoxyphenyl)-2,3-dihydro-1H-1-benzazepine-4-carboxylate (520 mg), and the solution was added dropwise to the previously prepared solution of formic anhydride in THF, at 0° C. The mixture was stirred at room temperature for 1.5 hours. The solvent was evaporated under reduced pressure, and the residue was diluted with ethyl acetate, washed with saturated sodium hydrogen carbonate solution, water and saturated brine, and dried with anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure to give crystals, which were washed with ethyl acetate/hexane to give methyl 1-formyl-7-(4-propoxyphenyl)-2,3-dihydro-1H-1-benzazepine-4-carboxylate (563 mg) as white crystals.
