Synthesis
General procedure for the synthesis of 5-bromo-2,3-diphenylpyrazine from 5,6-diphenyl-2-hydroxypyrazine: 5,6-diphenyl-2-hydroxypyrazine (2.48 g, 0.01 mol) was dissolved in 20 mL of anhydrous toluene under the condition of an ice bath and phosphorus tribromide (3.24 g, 0.012 mol) was added under nitrogen protection. The reaction mixture was stirred in an ice bath for 0.5 h before being heated and refluxed for 2 h. The reaction was completed with the addition of phosphorus tribromide. After completion of the reaction, it was cooled to room temperature and most of the solvent was removed by rotary evaporation. Ethyl acetate (50 mL) and ice water (20 mL) were added to the residue and the aqueous phase was extracted with ethyl acetate (50 mL x 3). The organic phases were combined and washed sequentially with cooled sodium bicarbonate solution (100 mL), water and saturated brine (200 mL × 2). The organic phase was dried with anhydrous sodium sulfate, filtered and rotary evaporated to give the crude product 5-bromo-2,3-diphenylpyrazine as a gray solid. The crude product was recrystallized with ethyl acetate, filtered and dried in vacuum to give 2.89 g of 5-bromo-2,3-diphenylpyrazine as a white solid in 93% yield.
References
[1] Patent: CN108623541, 2018, A. Location in patent: Paragraph 0111-0113; 0126; 0130-0132
[2] Patent: CN106632093, 2017, A. Location in patent: Paragraph 0009; 0010; 0011; 0012
[3] Journal of Heterocyclic Chemistry, 1999, vol. 36, # 3, p. 783 - 786
