1-Ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (268.1 g, 1.4 mol), triethylamine (280.0 mL), 5-formyl-2,4-dimethyl-1H-pyrrole-3-formic acid (167.0 g, 1.0 mol) and 1-hydroxybenzotriazole (189.2 g, 1.4 mol) were sequentially added to DMF (500 mL) with stirring at about 0° C., and stirred for 1.5 hrs, then (1-methylpyrrolidin-2-yl)ethylamine (1.2 mol) was added. The reaction was stirred at room temperature until completion was indicated by thin layer chromatography (TLC). 120 mL of water and 100 mL of saturated salt water were added, and the mixture was extracted with 10% methanol/dichloromethane (300 mL×3), the combined organic phase was washed with saturated salt water (300 mL×3), dried over anhydrous Na2SO4, and the solvent was distilled off under reduced pressure. The residue was then chromatographed on silica gel (eluted with methanol/ethyl acetate=1/1) to give 139.1 g (502 mmol) of N-[(1-methylpyrrolidin-2-yl)ethyl]-5-formyl-2,4-dimethyl-1H-pyrrole-3-formamide as an off-white solid. Yield 50.2%, m.p. 143-149° C.
