Synthesis and keto¯enol isomerism of 1-alkyl-2-methyl-5,6-dicyano-3-[2-(5alkylamino-2,3-dicyanopyrazin-6-yl)-1-hydroxyethenyl]-pyrrolo[2,3-b]pyrazine,

Reaction of 2-alkylamino-3-chloro-5,6-dicyanopyrazine 2 with 2,4-pentanedione in the presence of sodium hydride in benzene gave 2-methyl-3-acetyl-5,6-dicyanopyrrolo[2,3-b] pyrazine, which was further reacted with 2 to give the keto¯enol mixtures of 3-[1-hydroxy-2(3-alkylamino-5,6-dicyanopyrazine)-ethen-2-yl]-5,6-dicyanopyrrolo[2,3-b]pyrazine 4. The keto-form of 4 is colorless in chloroform but red in dimethylsulfoxide (DMSO) as an enolform. Their absorption spectra and electronic properties were correlated with their chemical structures.