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.

Synthesis of a library of benzoindolizines using poly(ethylene glycol) as soluble support.

A library of benzoindolizines (pyrrolo [1,5-a] quinolines 10 and pyrrolo [1,5-a] quinolines 9) has been synthesized using poly(ethylene glycol) (PEG) as soluble polymer support. The PEG-supported isoquinolinium salt 4 reacted, respectively, with active alkenes 11 using tetrakispyridinecobalt(II) dichromate (TPCD) as oxidant or alkynes 12 to give 10, of which yields were from moderate to high. By analogy, the reaction of PEG-supported quinolinium salt 3 with 12 was to produce 9. However, in the presence of TPCD the reaction of 3 with 11 afforded indolizines 8, which was discovered firstly.