Acylpyruvic acids readily react with 2,3-diaminopyridine to form (Z)-3-acyl
methylene-1H-3,4-dihydropyrido[2,3-b]pyrazin-2-ones. 5-Aryl-2,3-dihydrofura
n-2,3-diones which can be regarded as lactones derived from gamma -enolized
aroylpyruvic acids react with 2,3-diaminopyridine under mild conditions, y
ielding regioisomeric (Z)-2-aroylmethylene-4H+1,2-dihydropyrido[2,3-b]pyraz
in-3-ones. The structure of the products and reaction chemoselectivity are
discussed.