B. Preparation of methyl 2,6-dichloro-5-nitropyrimidine-4-carboxylate (Compound 3). Methyl 5-nitro-2,6-dioxo-1,2,3,6-tetrahydro-pyrimidine-4-carboxylate (Compound 2, 1.00 g, 3.97 mmol) was dissolved in phosphorus trichloride (4 mL). N,N-diethylaniline (1.3 mL) was added slowly and dropwise at room temperature. The reaction mixture was stirred at room temperature for 30 minutes, followed by heating and refluxing for 20 minutes. Upon completion of the reaction, the excess trichlorophosphorus was removed by concentration under reduced pressure. The concentrated oily residue was carefully poured into an ice-water mixture (10 mL) to quench the reaction. The aqueous phase was extracted with ethyl acetate (20 mL x 2) and the organic phases were combined. The organic phase was washed sequentially with 0.5 M hydrochloric acid (10 mL), saturated sodium bicarbonate solution (10 mL) and saturated saline (10 mL). The organic phase was dried over anhydrous sodium sulfate and concentrated under reduced pressure to give the yellow oily target product methyl 2,6-dichloro-5-nitropyrimidine-4-carboxylate (0.78 g, 78% yield). Mass spectrum (electrospray ionization) m/e 252 ([C6H3Cl2N3O4 + H]+).
