Hydrochloric Acid → 5-Nitro-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole--hydrogen chloride (1/1)

A mixture of 7.7 g of 5-nitro-1H-indole and 225 ml of ethanol saturated with hydrogen chloride and 22.5 g of the hydrate of 4-piperidone hydrochloride was refluxed for 3 hours under a nitrogen atmosphere and the mixture was then stirred at room temperature for one hour and at 0° C. for another hour. The mixture was filtered and the recovered product was rinsed with iced ethanol, with ethyl acetate and ether to obtain 14 g of raw product. The latter was crystallized from 600 ml of 1-1 methanol-water mixture and after standing overnight at 0° to 5° C., the mixture was filtered. The product was rinsed with methanol and dried to obtain 9.8 g of 3-(1,2,3,6-tetrahydro-4-pyridinyl)-5-nitro-1H-indole hydrochloride melting at 275° C.