[Synthesis]
Intermediate 1A: Preparation of 4-chloro-6-phenylpyrimidin-2-amine; Guanidine carbonate (3.60 g, 20 mmol) was suspended in ethanol (120 mL) and toluene (20 mL) and refluxed under nitrogen protection for 1 hour, during which time about 50 mL of solvent was removed by distillation. After the mixture was cooled to 45 °C, ethyl 3-oxo-3-phenylpropionate (7.68 g, 40 mmol) was added and refluxing was continued with heat overnight. During the reaction, the target product precipitated as a white solid. Water (50 mL) was added and reflux was continued for 30 minutes. After cooling to room temperature, the reaction mixture was neutralized with 1N HCl and allowed to stand in a refrigerator for 6 hours. The solid was collected by filtration, washed sequentially with water and ether, and dried under vacuum at 60 °C to give a white solid product (6.45 g, 86% yield). Mass spectrometry (MS ES): m/z 188 ([M + H]+, calculated value 188); measured value: 188. retention time (RT) = 0.91 min; thin-layer chromatography (TLC, unfolding reagent was 95/5 MeOH solution of CH2Cl2/2M NH3) Rf = 0.10. The above product (6.0 g, 32 mmol) was mixed with POCl3 (100 mL) was mixed and heated to reflux for 1 hr. Decompression distillation removed most of the POCl3 and the residue was diluted with EtOAc and poured into ice/saturated NaHCO3 solution. The aqueous layer was extracted with EtOAc, the organic layers were combined, washed with brine, dried over anhydrous Na2SO4 and concentrated. The crude product was recrystallized by EtOAc/ether to give the off-white powdery product 1A (2.8 g, 43% yield). Mass spectrometry analysis (MS ES): m/z 206 ([M + H]+, calculated value 206); retention time (RT) = 2.49 min; thin-layer chromatography (TLC, unfolding agent is 95/5 MeOH solution of CH2Cl2/2M NH3) Rf = 0.72. (Ref. 1: H.L. Skulnick, S.D. Weed, E.E. Edison, H.E. Renis, W. Wierenga, and D.A. Stringfellow, J. Med. Chem. 1985, 28, 1854-1869). |