Trifluoroacetic Acid Mediated One-Pot Synthesis of Furo-Fused Quinoxalines/Pyrazines

A trifluoroacetic acid promoted step-economical one-pot approach to the synthesis of furo-fused quinoxalines/pyrazines by the reaction of 2,3-dichloroquinoxalines/pyrazines with alkynes is described. The reaction involves a selective insitu Sonogashira coupling step and a hydroxylation followed by a metal-free 5-endo-dig cyclization. Preliminary experiments show that trifluoroacetic acid acts as a source of oxygen for the oxyarylation step, and isotopic labeling studies support the proposal that the mechanistic pathway involves activation of the alkyne by the acidic medium. Various kinds of substituents are tolerated, which should prove valuable for structural and biological investigations.