GENERAL METHOD: Ethyl sialic acid hydrochloride (10 mmol) was dissolved in ethanol (10 mL) and transferred to a round-bottomed flask equipped with a magnetic stirrer. After sealing the flask with a rubber stopper, a methanol solution of ammonia (10 mL) was slowly added to the reaction system via a syringe. The reaction mixture was stirred continuously at room temperature for 24 hours. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure and the resulting crude product was purified by rapid column chromatography on silica gel (eluent: ethyl acetate/methanol, 4:1, v/v) to afford 4-fluorobenzenemethanimidamide hydrochloride (1j) as a white solid in 87% yield (1.52 g, 8.7 mmol).
