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4.2.23 Synthesis of 1-(phenylsulfonyl)-1H-pyrrolo[2,3-b]pyridine-2-carboxylic acid (17): in a dry and nitrogen purged three-necked round bottom flask, 7-azaindole-1-benzenesulfonamide (5) (1.05 g, 4.07 mmol) was dissolved in anhydrous THF (15 mL) and cooled to -35 °C. Subsequently, lithium diisopropylammonium (5.1 mL, 10.16 mmol, 2M in THF) was slowly added. The reaction mixture was further cooled to -55 °C and dry ice (solid CO2) was slowly added. With stirring, the mixture was gradually warmed to room temperature and reacted overnight. Upon completion of the reaction, the reaction was quenched with water and extracted with ethyl acetate (EtOAc). The aqueous phase was acidified to pH=1 with 6N hydrochloric acid solution and extracted again with EtOAc. The organic phases were combined, washed with saturated sodium chloride solution, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to afford 1.09 g of the target product 1-(phenylsulfonyl)-1H-pyrrolo[2,3-b]pyridine-2-carboxylic acid (17) as a beige solid in 88% yield. The structure of the product was confirmed by 1H NMR and 13C NMR.1H NMR (300 MHz, DMSO-d6) δ (ppm): 13.87 (br, 1H), 8.51 (dd, J = 1.6, 4.7 Hz, 1H), 8.26 (d, J = 7.0 Hz, 2H), 8.13 (dd, J = 1.6, 7.9 Hz, 1H), 7.77 (dd, J = 7.2 Hz, 1H), 7.72-7.65 (m, 2H), 7.39 (dd, J = 4.7, 7.9 Hz, 1H), 7.28 (s, 1H).13C NMR (75 MHz, DMSO-d6) δ (ppm): 164.4, 149.5, 147.3, 138.5, 135.1, 133.3, 132.3, 132.1, 133.3, 133.3, 132.1 133.3, 132.1, 129.8 (2C), 128.3 (2C), 121.1, 120.7, 112.5.

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