Yield: 99%

Reaction Conditions:

Stage #1:7-Azaindole with tetrabutylammomium bromide;sodium hydroxide in dichloromethane
Stage #2:benzenesulfonyl chloride in dichloromethane at 0 - 20;

Steps:

4 4.2.4. 1-(Phenylsulfonyl)-1H-pyrrolo[2,3-b]pyridine (5)
4.2.4
1-(Phenylsulfonyl)-1H-pyrrolo[2,3-b]pyridine (5)
In a heat dried and nitrogen purged round bottom flask, 1H-pyrrolo[2,3-b]pyridine 1 (1.01 g, 8.58 mmol), tetrabutylammonium bromide (81 mg, 0.25 mmol), finely grounded sodium hydroxide (1.02 g, 25.41 mmol) and CH₂Cl₂ (20 mL) were mixed, stirred and cooled down to 0 °C in an ice bath, then benzene sulfonylchloride (1.35 mL, 10.59 mmol) was added slowly.
The mixture was left to warm up to room temperature and stirred at this temperature for 1 h.
The reaction was hydrolysed with water (20 mL) and extracted by CH₂Cl₂ (twice).
The organic layer was washed with a saturated sodium chloride solution, dried over magnesium sulfate and concentrated under reduced pressure to give 2.38 g of a beige solid.
The crude product was purified by chromatography on silica gel column, cyclohexane/EtOAc 7:3, to give 2.17 g of the pure expected product as a white solid in 99% yield. ¹H NMR (300 MHz, CDCl₃) δ (ppm): 8.45 (dd, J = 1.5, 4.8 Hz, 1H), 8.20 (d, J = 7.5 Hz, 2H), 7.86 (dd, J = 1.5, 7.8 Hz, 1H), 7.73 (d, J = 4.0 Hz, 1H), 7.57 (dd, J = 7.4 Hz, 1H), 7.52-7.47 (m, 2H), 7.19 (dd, J = 4.8, 7.8 Hz, 1H), 6.61 (d, J = 4.0 Hz, 1H).
¹³C NMR (75 MHz, CDCl₃) δ (ppm): 144.7 (2C), 138.3, 134.1, 129.9, 129.1 (2C), 128.0 (2C), 126.5, 123.0, 119.0, 105.5.

References:

Baltus, Christine B.;Jorda, Radek;Marot, Christophe;Berka, Karel;Bazgier, Václav;Kry?tof, Vladimír;Prié, Gildas;Viaud-Massuard, Marie-Claude [European Journal of Medicinal Chemistry,2016,vol. 108,p. 701 - 719]