General procedure for the synthesis of (1-hydroxymethylcyclopropyl)-tert-butoxycarbonylamino acids from ethyl 1-(BOC-amino)cyclopropanecarboxylate: ethyl 1-((tert-butoxycarbonyl)amino)cyclopropanecarboxylate (4.31 g, 18.80 mmol) was dissolved in tetrahydrofuran (THF, 20 mL), and a 2M lithium borohydride (LiBH4) THF solution was slowly added dropwise ( 10.34 mL, 20.68 mmol), and the reaction mixture was stirred at room temperature overnight. Subsequently, a THF solution of 2M LiBH4 (5 mL, 10 mmol) was added additionally and stirring was continued at room temperature for 6 hours. Upon completion of the reaction, anhydrous sodium sulfate (Na2SO4, 15 g) and water (H2O, 10 mL) were added and the suspension was stirred at room temperature over the weekend. The suspension was filtered through a pad of sodium sulfate and the residue was washed with dichloromethane (DCM). The combined filtrates were concentrated under reduced pressure and the product was purified by column chromatography (silica gel, heptane/ethyl acetate, 1:1) to give 2.78 g of the target product in 79% yield.
