A Comparison between KBH4 and NaBH4 in Their Reduction of Pyridinium Salts

General procedure for the synthesis of pyridinium salts.All reactions were run on the multi-gram scale, using the following general procedure. 1-Benzyl-4-(3-nitrophenyl)-pyridinium bromide (3a).Benzyl bromide (1.6 g, 9.4 mmol) was added to a solution of 4-(3-nitrophenyl)-pyridine 2a (1.6 g, 8.0 mmol) in acetone (20 mL).The resulting mixture was stirred at 60 °C for 10 h.The mixture was then cooled to 0 °C, and stirred for 20 minutes after petroleum ether (10 mL) was added.The mixture was filtrated to give white solid product 3a (2.5 g, 84%), which was ove1-dried and pure enough to use in the next step.mp 266-268 °C; 1 H NMR (500 MHz, DMSO-d 6 ) δ 9.36 (d, J = 6.8 Hz, 2H), 8.83 (s, 1H), 8.69 (d, J = 6.8 Hz, 2H), 8.50 -8.47 (m, 2H), 7.94 (t, J = 8.0 Hz, 1H), 7.61 -7.59 (m, 2H), 7.48 -7.44 (m, 3H), 5.91 (s, 2H); 13 C NMR (125 MHz, DMSO-d 6 ) δ 152.9, 148.5, 145.1,