To a stirred solution, under nitrogen, of 21.0 g (0.10 mole) of 1-(2-aminophenyl)indoline and 30.4 g (0.30 mole) of triethylamine in 400 ml of chloroform was added 29.9 g (0.15 mole) of 4-methyl-1-piperazinecarbonyl chloride hydrochloride in portions over about 5 minutes. The reaction was refluxed for 6 hours when an additional 10.1 g (0.10 mole) of triethylamine and 19.9 g (0.10 mole) of 4-methyl-1-piperazinecarbonyl chloride hydrochloride were added. After refluxing overnight (total of 25 hrs), the reaction was cooled, treated with 400 ml water, and stirred vigorously for 15 minutes. The layers were separated and the organic phase was washed twice with water, dried over Na2SO4, and concentrated in vacuo. The residue was dissolved in 100 ml of absolute ethanol and treated in one portion with a warm solution of 13.2 g (0.11 mole) of maleic acid in 50 ml of ethanol. After several hours, the crystals were collected, washed with ethanol, and dried to afford 19.2 g (43%), of product, m.p. 158° dec. An additional 4.5 g of pure salt was obtained from the mother liquor making the total amount of product 23.7 g and the yield 53%. 3.0 g of product were recrystallized from ethanol to provide 2.80 g of N-[2-(2,3-dihydro-1H-indol-1-yl)phenyl]-4-methyl-1-piperazinecarboximide maleate.
