5-(2-Diethylamino-ethyl)-3-methyl-4-oxo-1,4,5,6,7,8-hexahydro-pyrrolo[3,2-c]azepine-2-carboxylic acid tert-butyl ester 1i (0.413 g, 1.14 mmol) was dissolved in trifluoroacetic acid (1.5 ml, 20 mmol) under stirring, heated to 40° C. for 5 minutes in an oil bath under an argon atmosphere, and cooled down to −5° C. in an ice-salt bath under stirring, and added with triethoxy methane (0.34 ml, 1.7 mmol) and stirred for 2 minutes. Then the ice-salt bath was removed, and the reaction mixture was allowed to warm up to room temperature and stirred for another about 2 hours. After thin lay chromatography showed the disappearance of starting materials, the reaction mixture was added with 3 ml of ice water and 10 ml of dichloromethane, adjusted to pH 11 with aqueous sodium hydroxide solution (2 mol/L) and extracted with dichloromethane (10 ml×3). The combined organic extracts were dried over anhydrous magnesium sulfate, filtered to remove the drying agent and concentrated under reduced pressure to obtain yellow oil. The residue was purified by silica gel column chromatography to obtain the title compound 5-(2-diethylamino-ethyl)-3-methyl-4-oxo-1,4,5,6,7,8-hexahydro-pyrrolo[3,2-c]azepine-2-carbaldehyde 1j (0.271 g, yield 55%) as a light brown oil.
