The general procedure for the synthesis of 2,3-diamino-5-bromopyridine from 2-amino-3-nitro-5-bromopyridine is as follows:
Part I: Synthesis of imidazo[4,5-b]pyridin-2(3H)-one boronic acid
Step 1: Preparation of 5-bromopyridine-2,3-diamine
5-Bromo-3-nitropyridin-2-amine (3 g) was dissolved in a solvent mixture of isopropanol (56 mL) and water (28 mL). Ammonium chloride (1.47 g, 2 eq.) and iron powder (2.31 g, 3 eq.) were subsequently added. The reaction mixture was heated to 90°C and kept at this temperature for 45 minutes. Upon completion of the reaction, the mixture was cooled, diluted with ethyl acetate (EtOAc), filtered to remove insoluble matter, and the organic and aqueous layers were separated. The organic layer was subsequently washed with saturated brine, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target product 2,3-diamino-5-bromopyridine as a solid (2.45 g, 95% yield).
Product characterization data: 1H-NMR (300 MHz, DMSO-d6) δ 7.25 (d, 1H), 6.77 (d, 1H), 5.70-5.40 (bs, 2H), 5.20-4.80 (bs, 2H).
