General procedure for the synthesis of 7-azaindole-4-carboxaldehyde from 4-cyano-7-azaindole: Part 4: Preparation of 1H-pyrrolo[2,3-b]pyridine-4-carboxaldehyde: 1H-pyrrolo[2,3-b]pyridine-4-carbonitrile (200 mg, 1.4 mmol) was dissolved in tetrahydrofuran (7 mL) and cooled to -78°C under nitrogen protection. Diisobutylaluminum hydride (DIBAL-H, 1.0 M toluene solution, 3.07 mL, 3.07 mmol) was added slowly. The reaction mixture was stirred at -78 °C for 1 h. The temperature was gradually increased to 55 °C and stirring was continued for 2 h. The reaction mixture was then stirred at -78 °C for 1 h. Subsequently, DIBAL-H (1.4 mL, 1.4 mmol) was added supplementally and the mixture continued to stir at 55 °C for 2 hours. After completion of the reaction, the mixture was cooled to 5 °C, acidified with 2 M hydrochloric acid and stirred for 15 min. Next, the reaction mixture was neutralized with saturated aqueous sodium bicarbonate, the organic phase was extracted with dichloromethane (5 x 25 mL), the organic layers were combined and washed with brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to give 1H-pyrrolo[2,3-b]pyridine-4-carbaldehyde (107 mg, 52% yield). Mass spectrum (ES+): m/z 146 [MH+]. 1H NMR (DMSO-d6, 400 MHz): δ 7.22 (d, 1H, J = 3.6 Hz), 7.57 (d, 1H, J = 4.8 Hz), 7.67 (d, 1H, J = 2.4 Hz), 8.61 (d, 1H, J = 5.2 Hz), 10.42 (s, 1H) .
