Synthesis of Unexpected Pyrrolo[2,3-b]quinoxaline-2-carbaldehydes via Sonogashira Coupling Reaction

The reaction of a number of N-alkyl-3-chloroquinoxaline-2-amines with propargyl bromide in the presence of PdCl2(PPh3)2 and copper(I) iodide in wet morpholine leads to the formation of the unexpected N-substituted pyrrolo[2,3-b]quinoxaline-2-carbaldehydes in good yields. A possible mechanism for the conversion is suggested.