Diethyl Ether → 5-Bromo-7-hydroxy-1H-pyrrolo[2,3-b]pyridin-7-ium 3-chlorobenzoate

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Reaction Steps

5-Bromo-1H-pyrrolo[2,3-b]pyridine (20 g, 0.1 mol) was suspended in 300 mL of NMP. A solution of 3-Chloroperbenzoic acid (40 g, 0.16 mol) in 100 mL NMP was added dropwise over 30 min. The solution was stirred at 23° C. for 1 h after which 600 mL of ether were added. The grey precipitate was filtered off and washed with ether to yield 18 g of 5-Bromo-7-hydroxy-1H-pyrrolo[2,3-b]pyridin-7-ium 3-chlorobenzoate. The filtrate was stirred with 250 mL saturated sodium bicarbonate solution and 250 mL water to give 5-Bromo-1H-pyrrolo[2,3-b]pyridine 7-oxide (4.3 g, 20.2 mmol). The filtered 5-Bromo-7-hydroxy-1H-pyrrolo[2,3-b]pyridin-7-ium 3-chlorobenzoate was suspended in 200 mL of water and 200 mL of saturated sodium bicarbonate solution and was vigorously stirred for 1 h. The grey solids were filtered and washed with water to give a second crop of 5-Bromo-1H-pyrrolo[2,3-b]pyridine 7-oxide (11.15 g, 52.3 mmol, 71% combined yield). 1H NMR (500 MHz, DMSO-d6) δ 12.68 (s, 1H), 8.39 (d, J=1.5 Hz, 1H), 7.9 (d, J=1.5 Hz, 1H), 7.5 (d, J=3.5 Hz, 1H), 6.54 (d, J=3.5 Hz, 1H). MS: m/z 212.9 (M+H+).

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