PYRAZINE CHEMISTRY .10. SYNTHESIS OF ALKYLATED DERIVATIVES OF PIPERAZINE-2,5-DIONES

A general method is presented for the elaboration of 3-monosubstituted and 3,6-disubstituted piperazines and pyrazines. The method proceeds via prior formation of 2,5-diethoxy-3,6-dihydropyrazine, by reaction of the appropriate piperazine-2,5-dione with Meerwein's salt. These dihydropyrazines readily condense with either aldehydes or ketones and can be alkylated with alkyl or allyl bromides. Unsymmetrically substituted pyrazines can be prepared from the dihydro-intermediates by mild oxidation.