To a solution of ethyl 7-(2,2,2-trifluoroacetamido)thieno[2,3-b]pyrazine-6-carboxylate 10 (9.22 g, 28.9 mmol) and potassium carbonate (7.98 g, 57.8 mmol) in acetone (140 mL) was added iodomethane (3.60 mL, 57.8 mmol). The reaction was stirred at 50° C. for 1 h. NH4Cl solution(aq) was added and extracted with EtOAc. Organic layer was washed with brine, dried and evaporated to give crude ethyl 7-(2,2,2-trifluoro-N-methylacetamido)thieno[2,3-b]pyrazine-6-carboxylate 11 (9.1 g, 95%). (m/z)=334 (M+H)+.
