In step 3, 150 mL of cyclopentyl methyl ether (CPME) was added to the reaction flask and the temperature of the reaction system was controlled at -50 °C to -70 °C. Liquid ammonia (30.3 g, 1.78 mol) was slowly added dropwise followed by 2.5 M n-butyllithium (n-BuLi) solution 396 mL (0.99 mol). White solid formation was observed during the dropwise addition and the reaction was maintained at this temperature for 0.5 hr. Next, a mixed solution of (R)-tert-butyl thiobutyl tert-butyl tert-butyl tert-butyl sulfite (160.9 g, 0.83 mmol, 96.2% ee) and 2-chloropropane (86.4 g, 1.1 mmol) dissolved in cyclopentyl methyl ether was added dropwise (this solution was the reaction product of step 2). After the dropwise addition, the reaction was kept at a low temperature and continued to stir for 1 h. The completion of the reaction was monitored by TLC. At the end of the reaction, the reaction solution was concentrated under reduced pressure to remove the solvent, 1500 mL of methyl tert-butyl ether (MTBE) was added and filtered through diatomaceous earth. After the filtrate was concentrated under reduced pressure, 140 mL of cyclohexane was added, and the crystals were precipitated with stirring from -10 °C to 0 °C to obtain 79.5 g of white fine needle-like crystals of (R)-(+)-tert-butylsulfinamide in 79% yield. The product was analyzed by HPLC: purity 99.1%, enantiomeric excess value (ee) 99.8%.
