synthesis of 5-Fluorobarbituric acid: Urea (1.50 g, 25 mmol) was added to the solution of sodium (1.2 g, 53 mmol) in anhydrous ethanol (50 mL) and the mixture was heated to reflux. Diethyl 2-fluoromalonate (4.45 g, 25 mmol) was added dropwise over 10 minutes and the mixture was heated at reflux for 1h. After cooling to room temperature, the solution was filtered, the residue was washed with ethanol (20 mL), dissolved in water (30 mL) and acidified with HCl to pH 1. The precipitated product was recrystallized from the liquor to afford 5-fluorobarbituric acid (1.87 g, 51%) as a tan powder.
m.p.: >300 °C; ([M + H]+ , 147.0206, C4H4FN2O3 requires: [M]+ , 147.0204); IR (neat,cm-1 ) 2926, 2828, 1578, 1383, 1241, 1128; δF (D2O + NaOD, 376 MHz): -191.95 (s); δC (D2O + NaOD, 100 MHz) 131.89 (d, 1 JCF 214.4, C-F), 157.77 (d, 4 JCF 6.2, C-NH), 164.59 (d, 2 JCF 13.4, CvO); m/z (ASAP) 147 (25%, [M + H]+ ).18a
