Step 2: 4-Chloro-7-(phenylsulfonyl)-7H-pyrrolo[2,3-d]pyrimidine (3 g, 12.6 mmol, 1.0 eq.) and N,N,N',N'-tetramethylethylenediamine (TMEDA) (3.0 mL, 18.9 mmol, 1.5 eq.) were dissolved in tetrahydrofuran (THF) (120 mL), and cooled to -78 °C. The reaction was purified by adding n-butyl lithium (n-BuLi) (7.5 mL, 18.9 mmol, 1.5 eq.). Under stirring, n-butyllithium (n-BuLi) (7.5 mL, 18.9 mmol, 1.5 eq.) was slowly added. after 3 min, iodomethane (C3/4I) (3.7 mL, 59.2 mmol, 4.7 eq.) was added. The reaction mixture was kept stirred at -78 °C for 3 h, followed by a slow warming to room temperature over 1 h. The reaction was completed by the addition of iodomethane (C3/4I). Upon completion of the reaction, the reaction was quenched with saturated ammonium chloride (NH4Cl) solution (10 mL). Extraction was performed by adding ethyl acetate (EtOAc) (200 mL) and water (100 mL). The organic layer was separated, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford 7-benzenesulfonyl-4-chloro-6-methyl-7H-pyrrolo[2,3-d]pyrimidine as a brown solid (6.7 g, 90% yield).