Nitric Acid → 1-Methyl-4-nitro-1H-pyrrole-2-carbaldehyde

N-methylpyrrol-2-carboxaldehyde (5 g) was dissolved in anhydrous acetic acid (50 ml), and to an ice-cold of the solution was slowly added dropwise nitric acid (1.84 ml) with stirring. The mixture was stirred at this temperature for 1 hour, and then at room temperature for 18 hours. After confirming the completion of the reaction, to the mixture was added an ice-water (200 ml), followed by slowly adding solid sodium hydroxide (20 g) thereto and stirring for 1 hour. The obtained mixture was extracted with ether (150 ml×3). The obtained organic layer was washed with aqueous sodium bicarbonate solution and saturated aqueous sodium chloride solution, dried over sodium sulfate, and then filtered. The filtrate was concentrated under reduced pressure and purified by column-chromatography (ethyl acetate/hexane=1/4) to yield the compound 22-1 (3.5 g, 49.6%).