Access to functionalized 2-pyrones through cascade reactions of α-halothioesters involving DBU-derived ammonium ylides

Facile access to 4-aryl-6-oxycarbonyl-2-pyrones from α-halothioesters with β,γ-unsaturated α-keto esters is achieved via a DBU-promoted Michael addition/lactonization/elimination cascade reaction. The reaction mechanism is tentatively elucidated by performing control experiments and high-resolution mass spectrometry analysis, which indicates that the cascade sequence may involve DBU-derived ammonium ylides.