Synthesis
GENERAL METHOD: To a tetrahydrofuran (THF, 10 mL) solution of Fmoc-L-valine (10 mmol) was added N,N-diisopropylethylamine (DIPEA, 11 mmol, 1.42 mL) and 50% propylphosphonic anhydride (T3P) in ethyl acetate (EtOAc) solution (20 mmol, 6.36 mL) at 0 °C, and the reaction was stirred mixture for about 10 minutes. Subsequently, an aqueous solution (0.3 mL) of sodium borohydride (NaBH4, 10 mmol, 388 mg) was slowly added to the reaction mixture at the same temperature and stirring was continued until the reaction was shown to be complete by thin layer chromatography (TLC). After completion of the reaction, the solvent was removed under reduced pressure by rotary evaporator and the crude product was extracted with ethyl acetate (EtOAc). The organic phase was washed sequentially with 5% aqueous citric acid (10 mL × 2), 5% aqueous sodium carbonate (Na2CO3) (10 mL × 2), water and saturated saline. Finally, the organic phase was dried with anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure to afford the target product (S)-(9H-fluoren-9-yl)methyl (1-hydroxy-3-methylbutan-2-yl)carbamate.
References
[1] Journal of Organic Chemistry, 2001, vol. 66, # 25, p. 8454 - 8462
[2] Tetrahedron Letters, 1999, vol. 40, # 23, p. 4395 - 4396
[3] Tetrahedron Letters, 2012, vol. 53, # 38, p. 5059 - 5063
[4] RSC Advances, 2014, vol. 4, # 87, p. 46947 - 46950
[5] Organic and Biomolecular Chemistry, 2011, vol. 9, # 11, p. 4182 - 4187
