A 100 mL round-bottom flask was charged with 2-chloro-4-(morpholin-4-yl)benzaldehyde (0.800 g, 3.54 mmol, 1.00 equiv), tert-butyl (2S)-2-methylpiperazine-1-carboxylate (0.783 g, 3.91 mmol, 1.10 equiv), 1,2-dichloroethane (20 mL). The mixture was stirred for 30 min at room temperature. Sodium triacetoxyborohydride (2.26 g, 10.7 mmol, 3.00 equiv) was added. The resulting solution was stirred overnight at room temperature, diluted with H2O (30 mL), extracted with dichloromethane (3×30 mL) and the organic layers were combined, dried over Na2SO4, filtered and concentrated under reduced pressure. The residue was chromatographed on a silica gel column with ethyl acetate/petroleum ether (25/75) to provide 1.20 g (74% yield) of tert-butyl (2S)-4-[[2-chloro-4-(morpholin-4-yl)phenyl]methyl]-2-methylpiperazine-1-carboxylate as a white solid. LCMS (ESI, m/z): 410 [M+H]+.
