A mixture of 2-bromo-6-chloropyrazine (0.976 g, 5 mmol), Pd(PPh3)2Cl2 (0.106 g, 0.15 mmol), DIEA (0.646 g, 5 mmol) and CuI (0.095 g, 0.5 mmol) in DMF was purged with nitrogen and treated with trimethylsilylacetylene (0.491 g, 5 mmol). The resultant mixture was stirred at 23°C overnight. The reaction mixture was poured into saturated aqueous NaHCO3 and extracted with EtOAc. The organic layer was washed with brine, dried over Na2SO4, decanted and concentrated under reduced pressure. The crude product was purified by flash chromatography on silica gel (0- 20% EtOAc-hexanes) which gave the title compound 6a as a clear oil (861 mg, 80% yield).
Patent reference: WO2010016005 (Pfizer)