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(8) (Chem. Pharm. Bull. 1974, 22(2), 448-451). Boron oxide (720 mg, 10.26 mmol) and benzaldehyde (800 mg, 7.53 mmol) were added to a stirred solution of the indandione (1.00 g, 6.84 mmol) and piperidine (3 drops) in 10.2 ml of benzene. The solution was refluxed with stirring for 30 minutes. After filtration of the solution, the filtrate was concentrated under reduced pressure. The resulting crystalline solid was recrystallized from ethanol to afford 1.00 g (62.4%) of yellowish-green platelets: mp 149.5-150.0° C. (lit. mp 150° C., Okukawa, et al., Chem. Pharm. Bull., 1974, 22(2), 448-451). 1H NMR (250 MHz) δ 8.47-8.45 (m, 2H), 8.06-7.99 (m, 2H), 7.90 (s, 1H), 7.84-7.79 (m, 2H), 7.58-7.50 (m, 3H); 13C NMR (62.7 MHz) 190.5, 189.2, 147.2, 142.7, 140.2, 135.6, 135.4, 134.3, 133.4, 133.2, 129.3, 129.0, 123.5, 123.5 ppm.

1. temperatureThe solution was refluxed
2. filtrationAfter filtration of the solution
3. concentrationthe filtrate was concentrated under reduced pressure
4. customThe resulting crystalline solid was recrystallized from ethanol
5. customto afford 1.00 g (62.4%) of yellowish-green platelets