Step 9A: Synthesis of methyl 6-oxo-1,6-dihydropyrimidine-4-carboxylate. 6-Hydroxy-4-pyrimidinecarboxylic acid (36.0 g, 257 mmol) was dissolved in methanol (360 mL), and chlorotrimethylsilane (56 g, 554 mmol) was slowly added dropwise. The reaction mixture was stirred at room temperature for 8 hours. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. The residual solid was mixed with 200 mL of methanol and refluxed for 30 minutes. After cooling to room temperature, the precipitated solid was collected by filtration and washed with a small amount of methanol. The product was dried under vacuum at 35 °C to give 27.9 g (70% yield) of methyl 6-oxo-3,6-dihydropyrimidine-4-carboxylate.1H NMR (300 MHz, DMSO-d6) data were as follows: δ (ppm) 12.50 (broad single peak, 1H), 8.23 (single peak, 1H), 6.83 (single peak, 1H), 3.80 (single peak, 3H).
