The double addition of bis(trimethylsilyl) ketene acetals (1a–1b, R1 = CH3, –(CH2)5–) to 2-substituted pyrazines promoted by triflic anhydride leads to γ-lactones in a single step. A systematic study involving electron-withdrawing and electron-donating groups (R2 = CN, COOMe, PhCH=CH, Cl, Me, OMe) in the pyrazine ring reveals a strong dependence of electronic effects on the regiochemistry of nucleophilic addition.