Step 15A: Synthesis of methyl 2-oxo-1,2-dihydropyrimidine-4-carboxylate; To a methanolic (15 mL) suspension of 2-oxo-1,2-dihydropyrimidine-4-carboxylic acid (1.50 g, 10.7 mmol) was added chlorotrimethylsilane (2.36 g, 21.4 mmol) and the reaction mixture was heated and refluxed for 5.5 hours. After completion of the reaction, it was cooled to room temperature and the reaction mixture was concentrated to dryness. Methanol was added to the residue and concentrated again to obtain a suspension. The resulting solid was washed with water and methyl tert-butyl ether (MTBE), filtered and dried under reduced pressure at 40 °C for 1 h to afford the target product methyl 2-oxo-1,2-dihydropyrimidine-4-carboxylate (1.25 g, 76% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 8.28 (d, 1H), 6.88 (d, 1H), 3.86 (s, 3H).
