Trifluoroacetic acid → tert-Butyl 4-[(2-aminopyridin-3-yl)amino]piperidine-1-carboxylate

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Reaction Steps

A 50 mL 3-necked round bottom flask fitted with a thermometer and an overhead stirrer was charged with tert-butyl 4-oxopiperidine-1-carboxylate (3.00 g, 15.1 mmol) and acetonitrile (25 mL, HPLC grade). The reaction mixture was stirred at room temperature for 10 minutes to ensure complete dissolution of all solid material. Pyridine-2,3-diamine (1.50 g, 13.7 mmol) was added, the slurry was stirred for an additional 30 minutes, and resulted in the formation of a dark brown solution. The reaction mixture was cooled to 5° C. and trifluoroacetic acid (2 mL) was added over a period of 20 minutes. During the course of the addition, fuming was observed, accompanied by a slight temperature rise to 10-15° C. The reaction mixture was stirred for an additional 30 minutes at 5-10° C., and sodium triacetoxyborohydride (4.37 g, 20.6 mmol) was added over a period of 20 minutes. The ice bath was removed and the reaction mixture was stirred for an additional 30 minutes. The flask was placed back in an ice bath and aqueous 4M sodium hydroxide was added to the reaction in small portions to adjust the reaction mixture to pH 8. The solution was stirred for an additional 30 minutes, cooled to 5° C., and diluted with ice cold water (80 mL), and resulted in the formation of a brown precipitate. The resulting slurry was stirred overnight at room temperature. The solids were collected by vacuum filtration, washed with cold water (3×5 mL) and dried to constant weight to give 35.4 g (88% yield) of tert-butyl 4-(2-aminopyridin-3-ylamino)piperidine-1-carboxylate. This material was submitted to the next step without further purification. 1H NMR (400 MHz, DMSO-d6): δ 7.25 (dd, 1H), 6.64 (d, 1H), 6.17 (dd, 1H), 5.43 (broad s, 2H), 4.48 (d, 1H), 3.88 (d, 2H), 3.38 (broad s, 1H), 2.87 (broad s, 2.87), 1.87 (d, 2H), 1.38 (s, 9H), 1.19 (m, 2H). MS (EI) for C15H24N4O2: 293 (MH+)

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