General procedure for the synthesis of N-Boc-2-amino-5-bromopyrimidines from 2-amino-5-bromopyrimidines and di-tert-butyl dicarbonate: To a solution of 5-bromopyrimidin-2-amine (11, 5.22 g, 30 mmol) in N,N-dimethylformamide (DMF, 50 mL) was added sequentially 4-dimethylaminopyridine (DMAP, 366 mg, 3 mmol) and triethylamine (6.3 mL, 75 mmol) followed by slow addition of di-tert-butyl dicarbonate (17 mL, 75 mmol). The reaction mixture was stirred at 60 °C for 5 h. Upon completion of the reaction, the organic solvent was removed by rotary evaporator. Methanol (MeOH, 50 mL) and potassium carbonate (K2CO3, 2 eq.) were added to the residue and the mixture was continued to be stirred at 60 °C for 1.5 hours. The organic solvent was evaporated again and cold water (appropriate amount) was added to precipitate the product. The precipitate was collected by filtration, washed with water and dried to give an off-white solid 12 (7.38 g, 90% yield, Rf = 0.90, unfolding agent dichloromethane). The structure of the product was determined by nuclear magnetic resonance hydrogen spectrum (1H NMR, 400 MHz, DMSO-d6) δ: 10.21 (s, 1H), 8.71 (s, 2H), 1.44 (s, 9H); nuclear magnetic resonance carbon spectrum (13C NMR, 100 MHz, DMSO-d6) δ: 158.4, 156.5, 150.6, 112.3, 79.7 , 27.9; mass spectra (MS, ESI + APCI) m/z: 274.0 [M-H]-, 276.0 [M+H]+ for confirmation.
