ELECTROCHEMICAL AND CHEMICAL-REDUCTION OF FUROPYRAZINES, THIENOPYRAZINES, FUROQUINOXALINES, AND THIENOQUINOXALINES

The electrochemical reduction of furopyrazines, thienopyrazines, furoquinoxalines, and thienoquinoxalines was investigated in protic and aprotic mediums. The thieno[2,3-b]pyrazines and the thieno[3,4-b]pyrazines both lead, in aqueous medium, to a dihydro compound where the two nitrogen atoms of the pyrazine ring are hydrogenated. These primary reduction products isomerize in different ways: in the [2,3-b] series the thiophene ring is reduced while in the [3,4-b] series the pyrazine ring is reduced. These results can be rationalized on the basis of quantum calculations of the energies of the different isomers. These calculations also permit the explanation of the different reducibility between the two series of compounds.