General procedure for the synthesis of 2-bromo-5-iodopyrazine from 2-amino-5-bromopyrazine: to a solution of DME (30 mL) containing 2-amino-5-bromopyrazine (1.25 g, 7.2 mmol) was added sequentially CsI (1.86 g, 7.2 mmol), iodine (0.92 g, 3.6 mmol), CuI (0.42 g, 2.2 mmol) and isoamyl nitrite (5.8 mL, 43.2 mmol). The reaction mixture was heated to 60 °C and gas was observed to escape. After 35 min of reaction, the mixture was cooled to room temperature, extracted with saturated aqueous NH4Cl solution (100 mL) and EtOAc (100 mL) and filtered through diatomaceous earth. The organic layer was separated, washed with 5% Na2S2O3 solution, dried over MgSO4 and concentrated to give the yellow solid product 2-bromo-5-iodopyrazine (1.50 g, 74% yield).GC-MS analysis showed molecular ion peaks m/z of 284 and 286 (M+).
