Studies on the regioselective nucleophilic aromatic substitution (S(N)Ar) reaction of 2-substituted 3,5-dichloropyrazines.

Differences in regioselectivity were observed during the S(N)Ar reaction of amines with unsymmetrical 3,5-dichloropyrazines. This study revealed that when the 2-position of the pyrazine was occupied with an electron-withdrawing group (EWG), nucleophilic attack occurred preferentially at the 5-position. When the 2-position was substituted with an electron-donating group (EDG), nucleophilic attack occurred preferentially at the 3-position. These results are reported along with a computational rationale for the experimental observations based on the Fukui index at the reacting centers.