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A 3-l. three-necked flask, equipped with a thermometer and a mechanical stirrer was charged with 316 g (1.4 moles) of stannous chloride dihydrate and a solution of 111 g (3 moles) of dry hydrogen chloride gas in 1 l. of methyl alcohol. The colorless solution was stirred and cooled to -30° in a dry ice-acetone bath. 112.3 g (0.40 moles) of alpha-nitro-6-chloro-3-indoleacrylic acid methylester was added in 4 equal portions over 1 hour, maintaining the temperature between -25 and -20°. After the addition was complete, the temperature was allowed to rise to -10° and stirring at this temperature was continued for 90 minutes. Then 500 ml. of ether was added to the yellow suspension, followed by addition of 500 ml of 12N hydrochloric acid (concentrated), the temperature was kept below 5°. The mixture was then filtered through a Buchner funnel. The filter cake was washed with 1000 ml of methyl alcohol-9N aqueous hydrochloric acid 1:1, precooled to -20°, and 400 ml of ether. The tan product was dried at 40°/0.1 mmHg for 8 hours and then at 20°/0.1 mmHg to constant weight to yield 103.4 g (90%) of crude product, m.p. 191° (dec.).

1. customthree-necked flask, equipped with a thermometer and a mechanical stirrer
2. temperaturecooled to -30° in a dry ice-acetone bath
3. temperaturemaintaining the temperature between -25 and -20°
4. additionAfter the addition
5. customto rise to -10°
6. stirringstirring at this temperature
7. customwas kept below 5°
8. filtrationThe mixture was then filtered through a Buchner funnel
9. washThe filter cake was washed with 1000 ml of methyl alcohol-9N aqueous hydrochloric acid 1:1
10. customprecooled to -20°
11. customThe tan product was dried at 40°/0.1 mmHg for 8 hours