General procedure for the synthesis of 4-(methylamino)butan-1-ol from 4-amino-1-butanol and ethyl formate: ethyl formate (5.86 mL, 75.5 mmol) was added to a stirred ethanol (50 mL) solution of 4-amino-1-butanol (4.31 g, 48.4 mmol) and the mixture was stirred at reflux for 18 h under nitrogen protection. Upon completion of the reaction, the solvent was evaporated under reduced pressure and the resulting crude product was used directly in the next step of the reaction. The crude product was dissolved in tetrahydrofuran (25 mL) and slowly added dropwise to a suspension of lithium aluminum hydride (5.50 g, 145 mmol) in tetrahydrofuran (50 mL) under the protection of a drying tube. The reaction mixture was refluxed and the progress of the reaction was monitored by thin-layer chromatography (20% ethanol/80% chloroform) and nuclear magnetic resonance hydrogen spectroscopy (CDCl3).After 2 h, the feedstock was completely consumed, the reaction mixture was cooled, and water (4.16 mL), 4 M sodium hydroxide solution (4.16 mL) and water (12.5 mL) were added sequentially with vigorous stirring. Subsequently, the precipitate was removed by filtration and the filtrate was concentrated under vacuum. The residue was redissolved in chloroform, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give 4-(methylamino)butan-1-ol as a colorless oil (2.76 g, 56% yield). NMR hydrogen spectral (CDCl3) data: δ 3.74 (broad peak, 2H), 3.57 (triple peak, 2H), 2.62 (triple peak, 2H), 2.43 (single peak, 3H), 1.50-1.75 (multiple peaks, 4H).
