Copper(I) halide-promoted formation of 3-acyl-5-halopyridine moiety from NH-2-(2-acylethynyl)pyrroles and propargylamine

Available NH-2-acylethynylpyrroles undergo annulation/aromatization with propargylamine in the presence of 1 equiv. of CuHal (Hal=Cl, Br, I) at 60–65°C to afford 3-acyl-2-(pyrrol-2-yl)pyridines and their 5-halo analogues in 28–61 and 5–14% yields, respectively. The latter are assumed to be resulted from halohydrogenation of the intermediate Cu-pyrrolylpropargyl amino enones.