C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+].[NH2:15][C:16]1[C:21]([NH2:22])=[CH:20][CH:19]=[CH:18][N:17]=1.[C:23]([O:27][C:28]([N:30]1[CH2:35][CH2:34][C:33](=O)[CH2:32][CH2:31]1)=[O:29])([CH3:26])([CH3:25])[CH3:24]>ClC(Cl)C>[NH2:15][C:16]1[C:21]([NH:22][CH:33]2[CH2:34][CH2:35][N:30]([C:28]([O:27][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:29])[CH2:31][CH2:32]2)=[CH:20][CH:19]=[CH:18][N:17]=1Sodium triacetoxyborohydride (14.5 g, 68.7 mmol) was added to a solution of 2,3-diaminopyridine (5.00 g, 45.8 mmol) and N-(tert-butoxycarbonyl)-4-piperidone (9.58 g, 48.1 mmol) in dichloroethane (75 mL) at room temperature. After 5 h, additional sodium triacetoxyborohydride was added (1.8 g) and again after another 2.5 h. The reaction was stirred overnight, and quenched with 5% aqueous sodium hydroxide. This was extracted with methylene chloride, and washed with 5% aqueous sodium hydroxide, water and saturated sodium chloride solution. After drying over sodium sulfate, the solution was filtered and evaporated to give the crude product. This was purified by chromatography (silica gel, 3 to 5% methanol in methylene chloride gradient elution), which gave the title compound (4.44 g). MS 293 (M+1) 1H NMR (500 MHz, CD3OD) δ 7.32 (dd, J=5, 1 Hz, 1H), 6.85 (dd, J=8, 1 Hz, 1H), 6.59 (dd, J=8, 5 Hz, 1H), 4.04 (d, J=13 Hz, 2H), 3.46 (m, 1H), 2.98 (br s, 2H), 2.01 (dd, J=12, 2 Hz, 2H), 1.46 (s, 9H), 1.37 (qd, J=12, 4 Hz, 2H).
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