7,8-Diamino-3-(4-chlorophenyl)-2-isopropyl-chromen-4-one (168 mg, 0.511 mmol) is dissolved in 2,2-difluoropropionic acid (562 mg), dilute hydrochloric acid (2M, 0.1 ml) is added, and the mixture is heated at 110° C. for 4 h. The reaction mixture is cooled to room temperature, diluted with water (10 ml) and extracted with ethyl acetate (3×30 ml). The ethyl acetate extracts are combined and washed with saturated sodium bicarbonate solution (2×40 ml) and saturated brine (40 ml). The organic layer is dried (MgSO4), treated with decolourising charcoal (50 mg), filtered and evaporated to give a colourless solid. This is sonicated with n-hexane/diethyl ether and filtered to give a cream-coloured powder.
