Trimethylaluminum → 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

5-[3-(2-Diethylamino-ethylamino)-propyl]-3-methyl-1H-pyrrole-2,4-dicarboxylic acid 2-tert-butyl ester 4-ethyl ester 1 h (3.547 g, 8.67 mmol) was dissolved in 70 ml of toluene and stirred for 10 minutes at room temperature under an argon atmosphere. The mixture was added with a solution of trimethyl aluminum in toluene (5.6 ml, 2 mol/L, 11.27 mmol), and stirred for another 30 minutes at room temperature until no white smoke was released. The reaction mixture was heated to reflux for 4 hours in an oil bath. After thin lay chromatography showed the disappearance of starting materials, the reaction mixture was naturally cooled down to room temperature, quenched with ethanol (10 ml, 95%), and added with anhydrous ethanol (60 ml). The resulting mixture was filtered through a pad of Celite, washed with anhydrous ethanol (200 ml×4) and concentrated under reduced pressure. 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-carboxylic acid tert-butyl ester 1i (0.413 g, yield 75.7%) as a white solid.