To a solution of 2-amino-5-benzenesulfonyl-phenol (1.00 g., 4.016 mmol) in 20 mL dichlormethane was added 4-oxo-piperidine-1-carboxylic acid tert-butyl ester (0.880 g, 4.418 mmol) followed by sodium triacetoxyborohydride (1.78 g, 8.43 mmol) and the resulting suspension was stirred at room temperature under nitrogen for 24 hours. The reaction mixture was washed twice with 50 mL water, once with 50 mL brine, then dried over sodium sulfate and concentrated in vacuo. The resulting crude solid was purified by flash chromatography (20-30% ethyl acetate in hexanes) to give 1.823 g (4.53 mmol, 94%) of 4-(4-benzenesulfonyl-2-hydroxy-phenylamino)-piperidine-1-carboxylic acid tert-butyl ester as a foam. MS: 333 (M−CO2tBu+H)+, 377 (M−tBu+H)+.
