tert-Butyl piperidin-4-ylcarbamate (1.34 g, 6.69 mmol) was added to a solution of the aldehyde 47 (2.0 g, 4.46 mmol) in a mixture of NMP (20 mL) and glacial AcOH (0.250 mL). The reaction mixture was stirred for 30 min. NaBH(OAc)3 was then added and the reaction mixture was stirred for an additional 2.5 hours. The reaction mixture was then poured into a saturated aqueous NaHCO3 solution. A precipitate was formed which was collected by filtration, washed with water and air-dried. The crude material was purified by column chromatography using a 5 to 20% gradient of MeOH in EtOAc as eluent to afford the title compound 343 (1.45 g, 51.4% yield). MS (m/z): 633.6 (M+1)+.
