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##STR6## 19.2 g of 5,6-dimethoxyindanone, 15 g of pyridine-4-aldehyde and 19 g of p-toluenesulphonic acid were heated to boiling under reflux in a water separator for 5 h in 250 ml of toluene. The resulting precipitate was filtered off with suction after cooling and stirred at room temperature for 30 min in 10% strength sodium carbonate solution. The resulting pale-yellow precipitate was filtered off with suction, washed with water and dried in air. Yield: 24.4 g (87%).

1. filtrationThe resulting precipitate was filtered off with suction
2. temperatureafter cooling
3. filtrationThe resulting pale-yellow precipitate was filtered off with suction
4. washwashed with water
5. customdried in air