To a stirred solution of triphenylphosphine (1.178 g, 4.49 mmol) and imidazole (0.611 g, 8.98 mmol) in tetrahydrofuran (10 mL) at 0° C. was added iodine (1.292 g, 5.09 mmol). The resulting dark mixture was stirred at 0° C. After 5 minutes, tert-butyl 4-(2-(2-hydroxyethylthio)-5-nitrophenylamino)piperidine-1-carboxylate (1.19 g, 2.99 mmol) was added as a solution in tetrahydrofuran (5 mL). The mixture was then warmed to room temperature and stirred for 1 hour. The mixture was then diluted with ethyl acetate and washed with saturated sodium carbonate, saturated sodium thiosulfate, water, and brine. The organic phase was dried, filtered, concentrated, and then chromatographed in 1:2 ethyl acetate:hexanes, giving the desired product (1.50 g, 99%) as an orange foam. 1H NMR (DMSO-d6) δ 7.59-7.54 (m, 1H), 7.45-7.38 (m, 2H), 5.45-5.37 (m, 1H), 3.98-3.85 (m, 2H), 3.73-3.61 (m, 1H), 3.35-3.27 (m, 5H), 3.19-3.03 (m, 1H), 3.02-2.82 (m, 2H), 1.92-1.84 (m, 2H), 1.45-1.34 (m, 11H); ESI-MS (m/z, %): 530 (M+Na, 6), 452 (25), 279 (100).
