Heteroannulation through copper catalysis: a novel cyclisation leading to an unusual formation of 2-aroylquinoxalines

N-[(3′-Aryl)prop-2′-ynyl]-N,N′-1,2-phenylene di-p-tosylamides, 15–22, underwent an unusual ring closure with potassium carbonate (2 equiv.) and copper(I) iodide (10 mol%) in DMF at 100°C for 24 h to yield 2-aroylquinoxalines (23–30) instead of the expected 2-alkylidene-1,4-di-tosyl-1,2,3,4-tetrahydroquinoxalines (31).