GENERAL STEPS: To a solution of 6-azaindole (0.400 g; 3.386 mmol) in a solvent mixture of 1,2-dichloroethane (10 mL) and nitromethane (10 mL), cooled to 0°C. A mixture of 1,1-dichlorodimethyl ether (1.544 mL; 16.92 mmol) and aluminum trichloride (1.500 g; 11.25 mmol) was slowly added dropwise under argon protection for a controlled time of 1 hour. Upon completion of the reaction, the reaction was quenched by the addition of water and saturated sodium bicarbonate solution. The reaction mixture was extracted with a solvent mixture of dichloromethane and ethanol (9:1 v/v, 6 x 100 mL). The organic layers were combined, washed with saturated brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to afford the crude product 1H-pyrrolo[2,3-c]pyridine-3-carboxaldehyde (0.295 g, 60% yield), which could be used in the subsequent reaction without further purification. Product characterization data: ESI/APCI(+) m/z: 147 ([M + H]+); ESI/APCI(-) m/z: 145 ([M - H]-). 1H NMR (DMSO-d6) δ: 10.01 (1H, s), 8.88 (1H, s), 8.50 (1H, s), 8.33 (1H, d), 8.00 (1H, d). d).
