A mixture of 4-nitrobenzaldehyde (30.22 g, 0.2 mol), 1-dimethylethyl (2S)-2-methyl-1-piperazinecarboxylate (40.06 g, 0.2 mol) and sodium tri(acetoxy)borohydride (85 g, 0.4 mol) in 1,2-DCE (1 L) was stirred at room temperature over-weekend. The reaction mixture was treated portion-wise with NaHCO3 solution (400 mL) over a period of ˜2 h. After a further 30 mins, the organic layer was separated, washed with brine, dried and concentrated to give a viscous pale yellow oil. Purification by column chromatography eluting with 0%, 10% and then 20% EtOAc/hexane yielded the title compound as a yellow crystalline solid (61.1 g).
