General procedure for the synthesis of 1-methyl-4-(6-aminopyridin-3-yl)piperazine from 1-methyl-4-(6-nitropyridin-3-yl)piperazine: a mixture of 1-methyl-4-(6-nitropyridin-3-yl)piperazine (1.11 g, 5.02 mmol) and 10% Pd/C (110 mg) in methanol (15 mL) was stirred for 5 h at room temperature . Upon completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated to afford 951 mg (99% yield) of a yellow solid product, 1-methyl-4-(6-aminopyridin-3-yl)piperazine, which could be used in the subsequent reaction without further purification. The 1H NMR (CDCl3) data of the product were as follows: δ 7.78 (d, 1H, J = 3.0 Hz), 7.18 (dd, 1H, J = 3.0, 8.9 Hz), 6.48 (d, 1H, J = 8.9 Hz), 3.08 (dd, 4H, J = 4.9, 4.9 Hz), 2.61 (dd, 4H, J = 4.9, 4.9 Hz) , 2.37 (s, 3H).
