1) To a 500 mL four-necked reaction flask was added 152 g of diethyl malonate (0.95 mol) and 27.6 g of an isopropanol solution of 20% sodium isopropoxide (sodium isopropoxide content was 20%), and the reaction temperature was maintained at 25°C to 28°C. 46.5 g of 2-bromoethanol (0.372 mol) was started to be added dropwise, and then the temperature was raised to 50°C and the reaction was kept at a constant temperature for 1.5 h. After the reaction was completed, the solvent was removed by a rotary evaporator at less than 75°C and the reaction was completed. Upon completion of the reaction, the solvent was removed by rotary evaporator at less than 75°C to give diethyl 2-hydroxyethylmalonate, a colorless oily liquid with 97% purity (GC) and 94% yield.
2) To a 500 mL four-neck reaction flask was added 66.7 g of diethyl 2-hydroxyethyl malonate (0.317 mol) and 76.1 g of 20% sodium hydroxide solution, heated to 45°C, and reacted for 2 hours. After cooling to 25°C, 20% hydrochloric acid was added to adjust the pH to 6-7, then evaporated under reduced pressure at 80°C and filtered to obtain a colorless oily liquid 2-hydroxyethylmalonic acid 47.4 g (0.305 mol), purity 95% (GC), yield 96%.
3) To an autoclave was added 47.4 g of 2-hydroxyethylmalonic acid (0.305 mol), 50 g of water and 2.3 g of Cu/SiO2 catalyst. After purging the reaction vessel with nitrogen for 3-5 times, the reaction was carried out at 240°C for 4 hours. Upon completion of the reaction, the catalyst was removed by filtration to afford 36.2 g (0.280 mol) of 2-hydroxymethyl-1,4-butanediol as a colorless or light yellow oil with 96% purity (GC) and 95% yield.
4) To a 500 mL reaction flask equipped with a reflux condenser was added 36.2 g of 2-hydroxymethyl-1,4-butanediol (0.280 mol), 150 g of toluene and 1.6 g of methanesulfonic acid. After completion of the reaction, the solvent was removed by distillation under reduced pressure to afford 25.2 g (S)-tetrahydrofuran-3-methanol (0.192 mol) as a pale yellow oil with 95% purity (GC) and 86% yield.
