Sodium Dithionite → 6-Bromo-2-(4-methoxyphenyl)-7-(4-(pyridin-3-ylmethyl)piperazin-1-yl)-3H-imidazo[4,5-b]pyridine

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To a mixture of 5-bromo-3-nitro-4-(4-(pyridin-3-ylmethyl)piperazin-1-yl)pyridin-2-amine (0.043 g, 0.11 mmol) and ethanol (2.4 ml) was added 4-methoxybenzaldehyde (0.024 g, 0.18 mmol) with the aid of ethanol (1 ml) followed by a freshly prepared aqueous solution of Na2S2O4 (1M; 0.44 ml, 0.44 mmol). The reaction mixture was heated at 70° C. for 4.5 h, then allowed to cool to room temperature and the solvents were removed in vacuo. The residue was absorbed on silica gel and the free running powder was placed on a 10 g isolute silica column which was eluted with 50% ethyl acetate in dichloromethane, and then 3% to 6% methanol in ethyl acetate/dichloromethane (v/v; 1:1). The title compound was obtained as a yellow solid after trituration with diethyl ether (0.015 g, 28%); 1H-NMR (500 MHz, DMSO-d6) 2.62 (br s, 4H, piperazine N(CH2)2), 3.62 (s, 2H, NCH2CO), 3.66 (br s, 4H, piperazine N(CH2)2), 3.84 (s, 3H, OCH3), 7.10 (d, J=8.89 Hz, 2H) and 8.14 (d, J=8.57 Hz, 2H) (3,5-C6H4OMe and 2,6-C6H4—OMe), 7.39 (dd, J=7.91, 5.08 Hz, 1H, pyridyl 5-H), 7.76 (d, J=7.80 Hz, 1H, pyridyl 4-H), 8.20 (s, 1H, imidazo[4,5-b]pyridine 5-H), 8.50 (dd, J=4.76, 1.58 Hz, 1H, pyridyl 6-H), 8.56 (d, J=1.62 Hz, 1H, pyridyl 2-H), 13.37 (s, 1H, imidazo[4,5-b]pyridine N—H);

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