(R)-3-N-Boc-3-(methylamino)piperidine

Synthesis

1. At 0-5 °C, (R)-3-(tert-butoxycarbonylamino)piperidine (2.0 g, 10.0 mmol) was dissolved in THF (25 mL), triethylamine (1.67 mL, 12.0 mmol) was added, followed by the dropwise addition of benzyl chloroformate (1.55 mL, 11.0 mmol). The reaction was stirred by maintaining this temperature for 24 hours. Upon completion of the reaction, the mixture was concentrated under reduced pressure to 1/4 of the original volume and then liquid-liquid partitioned with EtOAc (20 mL) and 1M HCl solution (20 mL). The organic phase was washed sequentially with 1M HCl (10 mL), saturated aqueous NaHCO3 solution (10 mL) and brine (10 mL). The organic phase was dried over anhydrous MgSO4, filtered and concentrated under reduced pressure to afford the N-Cbz-protected intermediate as a colorless solid (3.2 g, 96% yield).LC/MS analysis showed a retention time of 6.58 min and [M+1]+ of 335. 2. The above N-Cbz-protected intermediate (1.67 g, 5.0 mmol) was dissolved in DMF (20 mL), cooled to 0-5 °C and 60% sodium hydride suspension (240 mg, 6.0 mmol) was added. The reaction mixture was slowly warmed to room temperature for 10 min, cooled again and then iodomethane (374 μL, 6.0 mmol) was added. After 2 hours of reaction, the reaction was warmed up to room temperature, iodomethane (40 μL, 1.0 mmol) was added additionally and stirring was continued for 16 hours. After completion of the reaction, the mixture was concentrated under reduced pressure to 1/4 of the original volume and liquid-liquid partitioned with EtOAc (50 mL) and water (50 mL). The organic phase was washed with brine (50 mL), dried over anhydrous MgSO4, filtered and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (eluent: EtOAc/hexane, 20% to 30%) to afford the N-methylated intermediate as a colorless oil (1.59 g, 93% yield). LC/MS analysis showed a retention time of 6.92 min and [M+1]+ of 349. 3. The N-methylated intermediate (1.56 g, 4.48 mmol) was dissolved in EtOH (50 mL), 10% palladium carbon (250 mg) was added, and hydrogenated at 60 °C for 6 h under 70 psi hydrogen pressure. Upon completion of the reaction, the crude reaction mixture was filtered through diatomaceous earth, concentrated under reduced pressure, redissolved in EtOH (5 mL) and filtered through a nylon syringe filter to remove residual catalyst. Final concentration under reduced pressure gave the crude product as a clear colorless oil. The product yield was quantified as in the final step and used directly in a subsequent reaction (Example 93).LC/MS analysis showed a retention time of 1.49 min and [M+1]+ of 215.

References

[1] Patent: US2009/62252, 2009, A1. Location in patent: Page/Page column 44
[2] Patent: WO2009/140320, 2009, A1. Location in patent: Page/Page column 75-76