91225-41-1

64-18-6

89123-58-0

91225-41-1

(b) 5-Bromo-2,3-diaminopyrazine (7.8 g, 41.3 mmol, 1 equiv) was added to a 250 mL reaction vial. 80 mL of N,N-dimethylformamide (DMF) was added with continuous stirring to dissolve 5-bromo-2,3-diaminopyrazine. Subsequently, triethyl orthoformate (7.34 g, 49.5 mmol, 1.2 eq.) and 20 mL of formic acid were added dropwise (at a rate of about 1 drop/second). The reaction mixture was heated to reflux and maintained under nitrogen protection for 24 hours (the reaction was monitored by thin layer chromatography (TLC) until the feedstock was essentially consumed). Upon completion of the reaction, the solvent was removed by distillation under reduced pressure and the residue was dissolved in methanol. Finally, purification by silica gel column chromatography afforded 5 g of 5-bromo-1H-imidazo[4,5-b]pyrazine.