Hydrochloric Acid → 9-Benzenesulfonyl-5-hydroxy-9H-dipyrido[2,3-b;4',3'-d]pyrrole-6-carbonitrile

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A mixture of 9-benzenesulfonyl-3-bromo-5-hydroxy-9H-dipyrido[2,3-b;4′,3′-d]pyrrole-6-carbonitrile (9.91 g, 23.1 mmol), palladium on carbon hydrogenation catalyst (10 wt %, 1.0 g, 0.94 mmol), ethanol (250 mL), ethyl acetate (50 mL), DMF (50 mL) and triethylamine (50 mL) was stirred at room temperature under an atmosphere of hydrogen for 16 hours. The catalyst was removed by filtration through Celite© and the filtrate evaporated to dryness to give a gum, that was mixed with hydrochloric acid (1M, 100 mL) and sonicated in a laboratory ultrasonic cleaning bath for 30 minutes. The resultant solid was collected by filtration, washed with water then dried under vacuum to afford the title compound as a tan coloured solid (7.19 g, 89%). 1H NMR (400 MHz, DMSO-d6): 9.27 (s, 1H), 8.71 (dd, J=4.9, 1.7 Hz, 1H), 8.68 (dd, J=7.9, 1.7 Hz, 1H), 8.20-8.20 (m, 2H), 7.74-7.73 (m, 1H), 7.60-7.59 (m, 3H).

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