Reaction of Acylpyruvic Acids and Their Esters with N-(2-Aminophenyl)acetamide

Acylpyruvic acids and their esters regioselectively reacted with N-(2-aminophenyl)acetamide to give acyclic enamines, substituted (Z)-2-[(2-acetamidophenyl)amino]-4-oxobut-2-enoates, whose structure was confirmed by X-ray analysis. These compounds were formed as a result of condensation involving the primary amino group of N-(2-aminophenyl)acetamide at the most electrophilic C2=O carbonyl group of acylpyruvic acid or its ester. The obtained enamines underwent thermal heterocyclization to (Z)-3-(2-oxoethylidene)-3,4-dihydroquinoxalin-2(1H)-ones having no substituent on the N1 atom rather than expected (Z)-1-acetyl-3-(2-oxoethylidene)-3,4-dihydroquinoxalin-2(1H)-ones. The heterocyclization involves intramolecular exchange between the amide and carboxylic acid (ester) fragments. The described transformations occur under mild conditions, require no catalyst or other additives, and therefore conform to the “green chemistry” principles. The products may be interesting from the viewpoints of medicinal chemistry, pharmacology, and fine organic synthesis.