General procedure for the synthesis of 3-bromo-4-chloro-7-azaindole from 4-chloro-7-azaindole: 1H-4-chloro-pyrrolo[2,3-b]pyridine (0.763 g, 5.0 mmol, 1.0 eq.) was dissolved in N,N-dimethylformamide (DMF, 7.5 mL, 1.5 mL/mmol of substrate), followed by addition of N-bromosuccinimide (NBS, 0.701 g, 5.25 mmol, 1.05 equiv). The reaction mixture was stirred overnight at room temperature protected from light. Upon completion of the reaction, ice water (25 mL, 5 mL/mmol substrate) was added to the mixture to quench the reaction and the precipitate precipitated was collected by filtration. The solid was washed four times with ice water (4 × 10 mL, 2 mL/mmol substrate) to remove residual DMF and by-products. The resulting solid was dried under high vacuum to afford 3-bromo-4-chloro-7-azaindole (0.861 g, 4.6 mmol) as an off-white solid in 92% yield. The melting point of the product was 236 °C (decomposition).1H NMR (300 MHz, DMSO-d6) δ: 7.21 (d, J = 4.2 Hz, 1H, H-5), 7.77 (s, 1H, H-2), 8.20 (d, J = 4.2 Hz, 1H, H-6), 12.35 (br.s, 1H, NH).13C NMR (75 MHz. DMSO-d6) δ: 101.1 (C-3), 113.7 (C-3a), 117.1 (C-5), 125.1 (C-2), 133.8 (C-4), 144.4 (C-6), 147.6 (C-7a). High-resolution mass spectrometry (HRMS, ESI): calculated value C7H5BrClN2 ([M + H]+) is 230.9319, measured value is 230.9319.
![1H-Pyrrolo[2,3-b]pyridine, 3-bromo-4-chloro-](/CAS2/GIF/1000340-39-5.gif)