Alkynyl- and dialkynyl-quinoxalines. Synthesis of condensed quinoxalines

Condensation of 2-chloro- and 2,3-dichloro-quinoxalines with alk-1-ynes in the presence of bis(triphenylphosphine)palladium(II) dichloride and copper(I) iodide gives mono- and di-alkynylquinoxalines. Addition of amines to these products gives stable enamines; hydration gives 2′-oxoalkyl compounds which exist predominantly in the intramolecularly hydrogen-bonded enol form. Condensation of the alkynylquinoxalines with diethyl sodiomalonate, and related compounds, yields pyrido[1,2-a]quinoxalin-4-one derivatives. 2-Alkynyl-3-chloro quinoxalines are intermediates for convenient syntheses of pyrrolo[2,3-b]quinoxalines.