General procedure for the synthesis of methyl 4-aminonicotinate from methyl 4-((tert-butoxycarbonyl)amino)nicotinate: 4-((tert-butoxycarbonyl)amino)nicotinate (9.08 g, 36.0 mmol) was dissolved in a 50/50 (v/v) trifluoroacetic acid (TFA)/dichloromethane (DCM) mixture (100 mL), and the reaction was stirred at room temperature for 2 hours. Upon completion of the reaction, the mixture was concentrated under reduced pressure to remove the solvent. Subsequently, the concentrate was redissolved in dichloromethane (100 mL), washed with saturated sodium bicarbonate solution, dried over anhydrous sodium sulfate and concentrated again under reduced pressure. Methyl 4-aminonicotinate (5.43 g, 99.1% yield) was finally obtained, the purity of which met the requirements of the subsequent reaction. The mass spectrum (chemical ionization, CI) showed a molecular ion peak (M/E) of 153.1.
