6.6 g of 4-chloro-2-nitrotoluene (compound 1c, 0.039 mol) and 23.0 g of DMFDMA (0.193 mol, 5 eq) were added to acetonitrile (80 mL). The reaction temperature was raised to 85 °C–95 °C and refluxed for 5 hours. The reaction was cooled, the solvent was evaporated to dryness, and the product was washed with water and a trace amount of ethanol to give 8.4 g of crude product 2c (0.0369 mol, yield 94.6%).
The obtained intermediate 2c was added to 118 mL of methanol containing 10 wt% hydrazine (hydrazine content 0.36 mol, 10 eq), and the temperature was raised to 50 °C. The reaction was carried out for 8 hours and then cooled to room temperature. The solvent was evaporated to dryness to give 5.4 g of product 3C,6-chloroindole (0.0355 mol, yield 96.3%).
