7-Benzyl-3-Boc-3,7-diazabicyclo[3.3.1]nonan-9-one

Synthesis

To a solution of methanol (20 mL) containing N-tert-butoxycarbonyl-4-piperidone (3 g, 15.06 mmol), benzylamine (1.73 mL, 15.81 mmol), and acetic acid (0.86 mL, 15.06 mmol) was added a suspension of paraformaldehyde (1 g, in 30 mL of methanol) under stirring. The reaction mixture was heated to reflux and stirred for 1 hour, followed by the addition of paraformaldehyde (1 g) and continued stirring for 4 hours. Upon completion of the reaction, the mixture was cooled to room temperature and concentrated. The concentrated residue was dissolved in ether (40 mL) and alkalized by adding 1M potassium hydroxide solution (20 mL). The organic layer was separated and the aqueous phase was extracted four times with ether. The organic phases were combined, dried with anhydrous sodium sulfate for 20 min, filtered and concentrated. The resulting yellow residue was purified by fast chromatography (silica gel 80 g, elution gradient: 0 to 50% ethyl acetate/hexane, 20 min) to afford tert-butyl 7-benzyl-9-oxo-3,7-diazabicyclo[3.3.1]nonane-3-carboxylate (5 g, 100% yield). lRMS (ESI): m/z Calculated value [M+H]+ 330.19, measured value 362.9 ([M+MeOH]+).

References

[1] Patent: WO2008/55068, 2008, A2. Location in patent: Page/Page column 176-177
[2] Patent: WO2009/137503, 2009, A1. Location in patent: Page/Page column 57-58
[3] Patent: US2017/749, 2017, A1. Location in patent: Paragraph 0558
[4] Tetrahedron, 2015, vol. 71, # 15, p. 2241 - 2245
[5] Chemical communications (Cambridge, England), 2002, # 7, p. 673 - 675