Ethyl 7-hydroxy-4-oxo-8-n-propyl-4H-1-benzopyran-2-carboxylate (1 g) in anhydrous dimethylformamide (4 ml) is cooled to 0° and treated under nitrogen with sodium hydride (50% dispersion in mineral oil, 180 mg) with stirring for 30 minutes. Dimethylaminothiocarbamylchloride (465 mg) is added and the mixture is stirred 15 minutes at 0°, warmed to 80° and maintained as such for 18 hours. The mixture is cooled, diluted with methylene chloride (50 ml) and washed with water (3×100 ml)), dried over sodium sulfate and reduced to dryness in vacuo. The residue is recrystallized from ethyl acetate and hexane to yield the title compound.
