Ammonia → 1-(2-Aminophenyl)-1'-methylspiro[indoline-3,4'-piperidine]dihydrochloride

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A large excess, about 20-25 g, of zinc dust is added portionwise to a vigorously stirring solution, at about 0° C., of 10.7 g of 1'-methyl-1-(2-nitrophenyl)spiro[indoline-3,4'-piperidine] (Example 15), in a combined solvent of 75 ml of ethanol and 5 ml of concentrated hydrochloric acid. After total addition, an additional 15 ml of concentrated hydrochloric acid is carefully added to maintain the temperature of the reaction mixture below 70° C. The reaction mixture is basified with concentrated ammonia, and the alkaline mixture is filtered and concentrated to dryness. The residue is partitioned between 400 ml of methylene dichloride and 400 ml of 10% sodium hydroxide. The organic portion is successively washed thrice with 400 ml portions of 10% sodium hydroxide and then once with a 400 ml portion of water, dried and concentrated to dryness, leaving a black glassy product. The product is converted to its hydrochloride in ether which is recrystallized from a methanol-ether mixture to leave the salt, mp 243° C., dec. of 1-(2-aminophenyl)-1'-methylspiro[indoline-3,4'-piperidine]-dihydrochloride.

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