239 mg (1.16 mmol) of 5-fluoro-2-methyl-4-oxo-4H-chromene-8-carbaldehyde, 0.14 ml (1.28 mmol) of 2,4-pentanedione, 0.085 ml (1.45 mmol) of acetic acid and 0.01 ml (0.12 mmol) of piperidine are heated under reflux in 25 ml of anhydrous dichloromethane for 3 h. After addition of 80 mg of pyridinium para-toluenesulfonate and heating under reflux for a further 12 h, the reaction solution is washed with water and with brine and concentrated. 308.4 mg (91% of theory) of a red oil are obtained and are directly reacted further.
