Synthesis
General procedure for the synthesis of N-BOC-4,4-difluoro-L-proline methyl ester from BOC-4-oxo-L-proline methyl ester: Intermediate 5a (300 g, 1.23 mmol, 1.00 eq.) was dissolved in dichloromethane (30 mL) at 0 °C, and DAST (1.80 g, 11.2 mmol, 9.00 eq.) was slowly added dropwise to the dichloromethane (10 mL) solution. The reaction mixture was stirred overnight at room temperature. Upon completion of the reaction, the reaction mixture was washed sequentially with saturated aqueous sodium bicarbonate solution (1 x 30 mL) and brine (3 x 30 mL). The organic layer was separated, dried with anhydrous sodium sulfate and concentrated under reduced pressure to give Intermediate 5b (300 mg, 92% yield) as a yellow oil.
References
[1] Patent: WO2006/123257, 2006, A2. Location in patent: Page/Page column 70
[2] Patent: WO2013/96771, 2013, A1. Location in patent: Page/Page column 95
[3] Journal of the American Chemical Society, 2016, vol. 138, # 7, p. 2443 - 2453
[4] Journal of Medicinal Chemistry, 2018, vol. 61, # 17, p. 7589 - 7613
[5] Patent: WO2005/23762, 2005, A1. Location in patent: Page/Page column 72
