General procedure for the synthesis of 5-chloro-2-hydrazinopyridine from 2,5-dichloropyridine: A mixed solution of 2,5-dichloropyridine (7.4 g, 50.0 mmol) and hydrazine hydrate (101 mL, 3250 mmol) in pyridine (100 mL) was heated and refluxed for 6 hours. Upon completion of the reaction, the reaction solution was concentrated to dryness in vacuum. The resulting residue was dissolved in dichloromethane (500 mL) and washed sequentially with 1N aqueous sodium hydroxide (500 mL) and water (3 x 500 mL). The organic layer was dried with anhydrous magnesium sulfate, filtered and concentrated to dryness in vacuo to afford 5-chloro-2-hydrazinopyridine (2.95 g, 20.55 mmol, 41% yield) as a light yellow solid.1H NMR (300 MHz, DMSO-d6) δ 7.97 (d, J = 2.5 Hz, 1H), 7.67 (s, 1H), 7.50 (dd, J = 9.0, 2.6 Hz, 1H), 6.73 (dd, J = 9.0, 0.6 Hz, 1H), 4.17 (s, 2H); MS (ES+) m/z 144.2 ([M+H]+).
