A solution of 2-chloro-5-nitroaniline (1 g, 5.79 mmol) and tert-butyl 4-oxopiperidine-1-carboxylate (2.309 g, 11.59 mmol) in dichloroethane (15 mL) and acetic acid (0.995 mL, 17.38 mmol) was stirred at room temperature for 30 minutes. At this time, the reaction was treated with sodium triacetoxyborohydride (3.07 g, 14.49 mmol), and the resulting mixture was stirred over the weekend. Additional tert-butyl 4-oxopiperidine-1-carboxylate (2.309 g, 11.59 mmol), sodium triacetoxyborohydride (3.07 g, 14.49 mmol), and dichloroethane (15 mL) were added. Stirring was continued for 2 days. The mixture was then diluted with water and 1N sodium hydroxide (basified to pH 10) and then extracted with dichloromethane (3×). The combined organics were dried, filtered, concentrated, and then chromatographed in 1:19 ethyl acetate:hexanes, giving a yellow/orange foam (1.26 g, 61.1%). 1H NMR (DMSO-d6) δ 7.54 (d, J=8.7 Hz, 1H), 7.51 (d, J=2.4 Hz, 1H), 7.39 (dd, J=8.7, 2.4 Hz, 1H), 5.76-5.63 (m, 1H), 3.99-3.90 (m, 2H), 3.74-3.62 (m, 1H), 3.05-2.80 (m, 2H), 1.89-1.80 (m, 2H), 1.49-1.32 (m, 11H); ESI-MS (m/z, %): 378 (M+Na, 100), 356 (MH+, 40), 300 (62).
