General procedure: In a dry four-necked flask equipped with a dropping funnel and thermometer, 150 g of (S)-dimethyl 2-(((benzyloxy)carbonyl)amino)pentanediyl ester (η= 2) was added. After cooling the reaction system to 0-10 °C, 150 g of tetrahydrofuran was added to dissolve the feedstock. Subsequently, 29 g of sodium borohydride was slowly added and 72 g of anhydrous ethanol was added. The reaction was carried out at 10~15°C and terminated by dropwise addition of 90 g of acetic acid. The pH of the reaction solution was adjusted to 4~5 and extracted by adding 330 g of water and 350 g of ethyl acetate. The organic phase was separated, washed sequentially with sodium carbonate solution and saturated brine, dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated under reduced pressure (-0.1 MPa, temperature below 45 °C) to give a solid product. Beating with 102 g of n-heptane, filtration and drying gave 111.5 g of (R)-2-N-Cbz-aminopentane-1,5-diol (compound of formula IV) as a white solid. The yield was 90.8%, chemical purity 96.3% and optical purity 99.8%.
