Synthesis of 2-arylpyrido[3,4-b]pyrazine derivatives through condensation of 3,4-diaminopyridine with β-keto sulfoxides

The reaction between 3,4-diaminopyridine and α-methylsulfinylacetophenone in benzene containing acetic acid under reflux gave 2-phenylpyrido3,4-b]pyrazine. In this way, 2-(4-methoxyphenyl)pyrido3,4-b]-pyrazine and 2-(3,4-dimethoxyphenyl)pyrido3,4-b]pyrazine were obtained by condensation of 3,4-diaminopyridine with the corresponding α-methylsulfinylacetophenones.