Selective synthesis of N-substituted pyrrolo[1,2-a]pyrazin-1(2H)-one derivatives via alkyne cyclization

A novel and efficient synthesis of N-substituted pyrrolo-pyrazinone derivatives has been developed. A trichloroacetyl group connected to the pyrrole ring was converted into the desired carboxamide derivatives. Promoted by NaH, the pyrrole carboxamide derivatives underwent a tandem reaction with propargyl bromide to afford pyrrolo-pyrazinones with high efficiency under very mild conditions. The mechanism for the formation of the products is discussed and supported by DFT calculations.