Electrochemical reduction of pyridopyrazines

The electrochemical reduction of several pyrido[2,3-b]pyrazines in hydroorganic or aprotic media leads to 1,4-dihydro derivatives which can be isolated in some cases. Most of these derivatives isomerize into 1,2-, 3,4-, or 5,8-dihydro compounds. A molecule of alcohol is added to these last compounds in alkaline medium. The electrochemical reduction of 1,2- or 3,4-dihydro derivatives gives 1,2,3,4-tetrahydropyridopyrazines. In hydroorganic media, the 7-bromopyrido [2,3-b]pyrazines give a 1,4-dihydro compound which can either isomerize or debromhydrate. In an aprotic medium, the parent heterocycle is obtained. By electrochemical reduction of pyrido[3,4-b]pyrazines, 1,4-dihydro derivatives can be formed which isomerize. The 1,2- or 3,4-dihydro compounds thus obtained can be reduced at the electrode into 1,2,3,4-tetrahydro derivatives.