a) Synthesis of 5-bromo-2-(methylamino)pyridine and 5-bromo-2-(dimethylamino)pyridine
To an anhydrous DMF (40 mL) suspension of NaH (60% dispersed in mineral oil, 0.44 g, 11 mmol), solid 2-amino-5-bromopyridine (1.73 g, 10 mmol) was added in batches, with the addition process being controlled to be completed within 5-10 min. After the gas release slowed down, the resulting amber colored mixture was stirred for 15 minutes. Subsequently, iodomethane (0.61 mL, 10 mmol) was added all at once. The reaction mixture was stirred overnight at room temperature, after which it was concentrated under vacuum. The residue was diluted with 5% aqueous NH4Cl (30 mL) and extracted with CH2Cl2. The organic phases were combined, washed with brine, dried (MgSO4) and concentrated. The product was separated by rapid chromatography on silica gel (3% MeOH/CH2Cl2). 5-Bromo-2-(methylamino)pyridine (0.60 g, 32%) was obtained as a semi-solid: TLC (3% MeOH/CH2Cl2) Rf 0.35; MS (ES) m/e 187 (M + H)+. Also obtained was 5-bromo-2-(dimethylamino)pyridine (0.70 g, 34%) as a semi-solid: TLC (3% MeOH/CH2Cl2) Rf 0.77; MS (ES) m/e 201 (M + H)+.
